@article {4856, title = {Differentiating physical and biological storage of nitrogen along an intermittent Antarctic stream corridor}, journal = {Freshwater Science}, volume = {42}, year = {2023}, month = {09/2023}, abstract = {

In many temperate streams, biological uptake of N acts to attenuate the transport of excess N from allochthonous anthropogenic imports. Relatively few studies have determined how this N uptake relates to the magnitude of physical vs. biological N storage in the stream corridor, especially for intermittent systems where allochthonous N imports are often low and N transport may only occur during brief periods of streamflow. Glacial meltwater streams in the McMurdo Dry Valleys of Antarctica provide an excellent setting to quantify autochthonous N cycling and storage processes supported by abundant algal mats and well-connected hyporheic zones. We combined historic point-scale sediment and periphyton sample datasets with remote sensing-based modeling of periphyton coverage to estimate how much N was stored in periphyton biomass and the hyporheic zone of a 5-km long McMurdo Dry Valley stream corridor (\>100,000 m2). We contextualized these N storage calculations by estimating the magnitude of annual N imports to and exports from the stream corridor based on \>2 decades of streamflow and surface water data, source glacier ice cores and meltwater data, and past studies of local aeolian deposition and biological N fixation rates. We found that in this highly oligotrophic system, stream corridor-scale N storage was ~1000x that of total annual N import or export fluxes. More than 90\% of this temporarily stored N was autochthonous organic matter in the shallow (\<10 cm) hyporheic zone, which acts as a reservoir that sustains N availability in the water column. Despite its location in a polar desert devoid of higher-order vegetation, area-normalized N storage (~40 g N/m2) was greater than that reported for streams at lower latitudes (~1\–22 g N/m2). We also demonstrated that NH4+ sorption to stream sediment may be an important physicochemical N storage mechanism that responds to short-term fluctuations in streamflow and governs the mobility of inorganic N. Altogether, this research illustrates the importance of quantifying N storage within stream corridors when evaluating the significance of internal cycling and physical retention processes that modulate N availability.

}, keywords = {LTER-MCM, hyporheic zone, McMurdo LTER, nitrogen cycling, nutrient budget, organic matter, periphyton}, issn = {2161-9549}, doi = {10.1086/725676}, url = {https://www.journals.uchicago.edu/doi/10.1086/725676}, author = {Singley, Joel G. and Salvatore, Mark R. and Michael N. Gooseff and Diane M. McKnight and Eve-Lyn S. Hinckley} } @article {4839, title = {Impact of meltwater flow intensity on the spatiotemporal heterogeneity of microbial mats in the McMurdo Dry Valleys, Antarctica}, journal = {ISME Communications}, volume = {3}, year = {2023}, month = {01/2023}, pages = {3}, abstract = {

The meltwater streams of the McMurdo Dry Valleys are hot spots of biological diversity in the climate-sensitive polar desert landscape. Microbial mats, largely comprised of cyanobacteria, dominate the streams which flow for a brief window of time (~10 weeks) over the austral summer. These communities, critical to nutrient and carbon cycling, display previously uncharacterized patterns of rapid destabilization and recovery upon exposure to variable and physiologically detrimental conditions. Here, we characterize changes in biodiversity, transcriptional responses and activity of microbial mats in response to hydrological disturbance over spatiotemporal gradients. While diverse metabolic strategies persist between marginal mats and main channel mats, data collected from 4 time points during the austral summer revealed a homogenization of the mat communities during the mid-season peak meltwater flow, directly influencing the biogeochemical roles of this stream ecosystem. Gene expression pattern analyses identified strong functional sensitivities of nitrogen-fixing marginal mats to changes in hydrological activities. Stress response markers detailed the environmental challenges of each microhabitat and the molecular mechanisms underpinning survival in a polar desert ecosystem at the forefront of climate change. At mid and end points in the flow cycle, mobile genetic elements were upregulated across all mat types indicating high degrees of genome evolvability and transcriptional synchronies. Additionally, we identified novel antifreeze activity in the stream microbial mats indicating the presence of ice-binding proteins (IBPs). Cumulatively, these data provide a new view of active intra-stream diversity, biotic interactions and alterations in ecosystem function over a high-flow hydrological regime.

}, keywords = {LTER-MCM}, doi = {10.1038/s43705-022-00202-8}, url = {https://www.nature.com/articles/s43705-022-00202-8}, author = {Zoumplis, Angela and Kolody, Bethany C. and Kaul, Drishti and Zheng, Hong and Venepally, Pratap and Diane M. McKnight and Cristina D. Takacs-Vesbach and DeVries, Arthur L. and Allen, Andrew E.} } @article {4867, title = {Long-term changes in concentration and yield of riverine dissolved silicon from the poles to the tropics}, journal = {Global Biogeochemical Cycles}, year = {2023}, month = {08/2023}, abstract = {

Riverine exports of silicon (Si) influence global carbon cycling through the growth of marine diatoms, which account for \∼25\% of global primary production. Climate change will likely alter river Si exports in biome-specific ways due to interacting shifts in chemical weathering rates, hydrologic connectivity, and metabolic processes in aquatic and terrestrial systems. Nonetheless, factors driving long-term changes in Si exports remain unexplored at local, regional, and global scales. We evaluated how concentrations and yields of dissolved Si (DSi) changed over the last several decades of rapid climate warming using long-term datasets from 60 rivers and streams spanning the globe (e.g., Antarctic, tropical, temperate, boreal, alpine, Arctic systems). We show that widespread changes in river DSi concentration and yield have occurred, with the most substantial shifts occurring in alpine and polar regions. The magnitude and direction of trends varied within and among biomes, were most strongly associated with differences in land cover, and were often independent of changes in river discharge. These findings indicate that there are likely diverse mechanisms driving change in river Si biogeochemistry that span the land-water interface, which may include glacial melt, changes in terrestrial vegetation, and river productivity. Finally, trends were often stronger in months outside of the growing season, particularly in temperate and boreal systems, demonstrating a potentially important role of shifting seasonality for the flux of Si from rivers. Our results have implications for the timing and magnitude of silica processing in rivers and its delivery to global oceans.

}, keywords = {LTER-MCM, biogeochemistry, river, silica, silicon, stream, trends}, issn = {0886-6236}, doi = {10.1029/2022GB007678}, url = {https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GB007678}, author = {Jankowski, Kathi Jo and Johnson, Keira and Sethna, Lienne and Julian, Paul and Wymore, Adam S. and Shogren, Arial J. and Thomas, Patrick K. and Sullivan, Pamela L. and Diane M. McKnight and McDowell, William H. and Heindel, Ruth C and Jones, Jeremy B. and Wollheim, Wilfred and Abbott, Benjamin and Deegan, Linda and Carey, Joanna C.} } @article {4864, title = {Nitrogen fixation facilitates stream microbial mat biomass across the McMurdo Dry Valleys, Antarctica}, journal = {Biogeochemistry}, year = {2023}, month = {07/2023}, abstract = {

Nitrogen (N) fixation is a fundamental mechanism by which N enters streams. Yet, because of modern N saturation, it is difficult to study the importance of N-fixation to stream nutrient budgets. Here, we utilized relatively simple and pristine McMurdo Dry Valley streams to investigate the role of N-fixing Nostoc abundance, streamwater dissolved inorganic N (DIN) concentration, and distance from the source glacier in regulating the elemental and isotopic composition of three microbial mat types (black, orange, and green) at the landscape scale. We found Nostoc-based black mats were the most enriched in δ15N, and δ15N signatures of mats increased where Nostoc was abundant, but did not surpass the atmospheric standard (δ15N \≈ 0\‰). Furthermore, green and orange mat δ15N signatures became more depleted with increasing DIN, indicating that mats utilize glacial meltwater-sourced N when available. The distance from the source glacier explained limited variability in mat δ15N across sites, indicating the influence of individual stream characteristics on N spiraling. To further explore longitudinal N spiraling processes generating observed δ15Ν patterns, we developed a simple steady-state mathematical model. Analysis of plausible scenarios with this model confirmed that streams both have the capacity to remove allochthonous DIN over the plausible range of inputs, and that internal N sources are required to account for δ15N signatures and observed DIN concentrations at stream outlets. Collectively, these data and modeling results demonstrate that N-fixation exerts substantial influence within and across these streams, and is presumably dependent upon interconnected organic matter reserves, mineralization rates, and geomorphology.

}, keywords = {LTER-MCM, biofilm, C, cyanobacteria, hyporheic zone, MCM LTER, mineralization, N, P biogeochemistry}, doi = {10.1007/s10533-023-01069-0}, url = {https://link.springer.com/article/10.1007/s10533-023-01069-0}, author = {Tyler J. Kohler and Singley, Joel G. and Wlostowski, Adam and Diane M. McKnight} } @article {4814, title = {Antarctic lake phytoplankton and bacteria from near-surface waters exhibit high sensitivity to climate-driven disturbance}, journal = {Environmental Microbiology}, year = {2022}, month = {07/2022}, abstract = {

The McMurdo Dry Valleys (MDVs), Antarctica, represent a cold, desert ecosystem poised on the threshold of melting and freezing water. The MDVs have experienced dramatic signs of climatic change, most notably a warm austral summer in 2001\–2002 that caused widespread flooding, partial ice cover loss and lake level rise. To understand the impact of these climatic disturbances on lake microbial communities, we simulated lake level rise and ice-cover loss by transplanting dialysis-bagged communities from selected depths to other locations in the water column or to an open water perimeter moat. Bacteria and eukaryote communities residing in the surface waters (5 m) exhibited shifts in community composition when exposed to either disturbance, while microbial communities from below the surface were largely unaffected by the transplant. We also observed an accumulation of labile dissolved organic carbon in the transplanted surface communities. In addition, there were taxa-specific sensitivities: cryptophytes and Actinobacteria were highly sensitive particularly to the moat transplant, while chlorophytes and several bacterial taxa increased in relative abundance or were unaffected. Our results reveal that future climate-driven disturbances will likely undermine the stability and productivity of MDV lake phytoplankton and bacterial communities in the surface waters of this extreme environment.

}, keywords = {LTER-MCM}, doi = {10.1111/1462-2920.16113}, url = {https://onlinelibrary.wiley.com/doi/10.1111/1462-2920.16113}, author = {Sherwell, Shasten S. and Kalra, Isha and Li, Wei and Diane M. McKnight and John C. Priscu and Rachael M. Morgan-Kiss} } @article {4713, title = {Blowin{\textquoteright} in the wind: Dispersal, structure, and metacommunity dynamics of aeolian diatoms in the McMurdo Sound region, Antarctica}, journal = {Journal of Phycology}, volume = {58}, year = {2022}, month = {02/2022}, pages = {36-54}, abstract = {

Diatom metacommunities are structured by environmental, historical, and spatial factors that are often attributed to organism dispersal. In the McMurdo Sound region (MSR) of Antarctica, wind connects aquatic habitats through delivery of inorganic and organic matter. We evaluated the dispersal of diatoms in aeolian material and its relation to the regional diatom metacommunity using light microscopy and 18S rRNA high-throughput sequencing. The concentration of diatoms ranged from 0 to 8.76 * 106 valves \· g-1 dry aeolian material. Up to 15\% of whole cells contained visible protoplasm, indicating that up to 3.43 * 104 potentially viable individuals could be dispersed in a year to a single 2 cm2\ site. Diatom DNA and RNA was detected at each site, reinforcing the likelihood that we observed dispersal of viable diatoms. Of the 50 known morphospecies in the MSR, 72\% were identified from aeolian material using microscopy. Aeolian community composition varied primarily by site. Meanwhile, each aeolian community was comprised of morphospecies found in aquatic communities from the same lake basin. These results suggest that aeolian diatom dispersal in the MSR is spatially structured, is predominantly local, and connects local aquatic habitats via a shared species pool. Nonetheless, aeolian community structure was distinct from that of aquatic communities, indicating that intrahabitat dispersal and environmental filtering also underlie diatom metacommunity dynamics. The present study confirms that a large number of diatoms are passively dispersed by wind across a landscape characterized by aeolian processes, integrating the regional flora and contributing to metacommunity structure and landscape connectivity.

}, keywords = {LTER-MCM, 18S rRNA, airborne, algae, assembly, Bacillariophyta, biogeography, connectivity, high-throughput sequencing}, issn = {0022-3646}, doi = {10.1111/jpy.13223}, url = {https://onlinelibrary.wiley.com/doi/10.1111/jpy.13223}, author = {Schulte, Nicholas O. and Khan, Alia L. and Smith, Emma W. and Zoumplis, Angela and Kaul, Drishti and Allen, Andrew E. and Adams, Byron J. and Diane M. McKnight} } @article {4815, title = {Dissolved organic carbon chemostasis in Antarctic polar desert streams}, journal = {Journal of Geophysical Research: Biogeosciences}, volume = {127}, year = {2022}, month = {07/2022}, pages = {e2021JG006649}, abstract = {

Dissolved organic carbon (DOC) is a key variable impacting stream biogeochemical processes. The relationship between DOC concentration (C) and stream discharge (q) can elucidate spatial and temporal DOC source dynamics in watersheds. In the ephemeral glacial meltwater streams of the McMurdo Dry Valleys (MDV), Antarctica, the C-q relationship has been applied to dissolved inorganic nitrogen and weathering solutes including silica, which all exhibit chemostatic C-q behavior; but DOC-q dynamics have not been studied. DOC concentrations here are low compared to temperate streams, in the range of 0.1-2 mg C l-1, and their chemical signal clearly indicates derivation from microbial biomass (benthic mats and hyporheic biofilm). To investigate whether the DOC generation rate from these autochthonous organic matter pools was sufficient to maintain chemostasis for DOC, despite these streams\&$\#$39; large diel and interannual fluctuations in discharge, we fit the long-term DOC-q data to a power law and an advection-reaction model. Model outputs and coefficients of variation characterize the DOC-q relationship as chemostatic for several MDV streams. We propose a conceptual model in which hyporheic carbon storage, hyporheic exchange rates, and net DOC generation rates are key interacting components that enable chemostatic DOC-q behavior in MDV streams. This model clarifies the role of autochthonous carbon stores in maintaining DOC chemostasis and may be useful for examining these relationships in temperate systems, which typically have larger sources of bioavailable autochthonous organic carbon than MDV streams but where this autochthonous signal could be masked by a stronger allochthonous contribution.

}, keywords = {LTER-MCM, Antarctica, chemostasis, concentration-discharge, DOC, ephemeral streams, LTER}, doi = {10.1029/2021JG006649}, url = {https://onlinelibrary.wiley.com/doi/10.1029/2021JG006649}, author = {Torrens, Christa L. and Michael N. Gooseff and Diane M. McKnight} } @article {4627, title = {Connectivity: Insights from the U.S. Long Term Ecological Research Network}, journal = {Ecosphere}, volume = {12}, year = {2021}, month = {05/2021}, pages = {e03432}, abstract = {

Ecosystems across the United States are changing in complex and surprising ways. Ongoing demand for critical ecosystem services requires an understanding of the populations and communities in these ecosystems in the future. This paper represents a synthesis effort of the U.S. National Science Foundation-funded Long-Term Ecological Research (LTER) network addressing the core research area of \“populations and communities.\” The objective of this effort was to show the importance of long-term data collection and experiments for addressing the hardest questions in scientific ecology that have significant implications for environmental policy and management. Each LTER site developed at least one compelling case study about what their site could look like in 50\–100 yr as human and environmental drivers influencing specific ecosystems change. As the case studies were prepared, five themes emerged, and the studies were grouped into papers in this LTER Futures Special Feature addressing state change, connectivity, resilience, time lags, and cascading effects. This paper addresses the \“connectivity\” theme and has examples from the Phoenix (urban), Niwot Ridge (alpine tundra), McMurdo Dry Valleys (polar desert), Plum Island (coastal), Santa Barbara Coastal (coastal), and Jornada (arid grassland and shrubland) sites. Connectivity has multiple dimensions, ranging from multi-scalar interactions in space to complex interactions over time that govern the transport of materials and the distribution and movement of organisms. The case studies presented here range widely, showing how land-use legacies interact with climate to alter the structure and function of arid ecosystems and flows of resources and organisms in Antarctic polar desert, alpine, urban, and coastal marine ecosystems. Long-term ecological research demonstrates that connectivity can, in some circumstances, sustain valuable ecosystem functions, such as the persistence of foundation species and their associated biodiversity or, it can be an agent of state change, as when it increases wind and water erosion. Increased connectivity due to warming can also lead to species range expansions or contractions and the introduction of undesirable species. Continued long-term studies are essential for addressing the complexities of connectivity. The diversity of ecosystems within the LTER network is a strong platform for these studies.

}, keywords = {LTER-MCM, alpine tundra, Antarctic polar desert, arid grassland, arid shrubland, coastal, estuary, salt marsh, Special Feature: Forecasting Earth{\textquoteright}s Ecosystems with Long-Term Ecological Research, urban ecosystem}, issn = {2150-8925}, doi = {10.1002/ecs2.v12.510.1002/ecs2.3432}, url = {https://onlinelibrary.wiley.com/doi/10.1002/ecs2.3432}, author = {Iwaniec, David M. and Michael N. Gooseff and Suding, Katharine N. and Johnson, David Samuel and Reed, Daniel C. and Debra P. C. Peters and Byron Adams and John E. Barrett and Bestelmeyer, Brandon T. and Castorani, Max C. N. and Cook, Elizabeth M. and Davidson, Melissa J. and Groffman, Peter M. and Hanan, Niall P. and Huenneke, L and Johnson, Pieter T. J. and Diane M. McKnight and Miller, Robert J. and Okin, Gregory S. and Preston, Daniel L. and Rassweiler, Andrew and Ray, Chris and Osvaldo E. Sala and Schooley, Robert and Seastedt, Timothy and Spasojevic, Marko J. and Vivoni, Enrique R.} } @mastersthesis {4762, title = {Controls on microbial mat coverage and diatom species turnover in Antarctic desert streams: A transplant experiment}, volume = {M.S.}, year = {2021}, school = {University of Colorado Boulder}, type = {masters}, address = {Boulder, CO}, abstract = {

This thesis evaluates how polar desert streams regulate benthic microbial mat coverage, chlorophyll-a biomass, and diatom species composition. Microbial mats growing on rocks (eplithon) and on sandy substrate (epipelon) were reciprocally transplanted among four glaciers meltwater streams and monitored through time. The selected study streams were Green Creek, Bowles Creek, Delta Stream, Von Guerard Stream in the Lake Fryxell Basin in the McMurdo Dry Valleys, Antarctica. These streams vary in length, streamflow intermittency, and diatom community composition of microbial mats. Results demonstrate that streams strongly control mat biomass (coverage and chlorophyll-a) differently for epilithon and epipelon. However, diatom species composition did not vary between these growth habitats but instead varied by stream, suggesting adaptive niche separation related to environmental conditions. Diatom species composition of transplants in Green Creek became dissimilar from their initial stream communities suggesting downstream dispersal and within stream connectivity regulates community assembly. This experiment confirms that environmental characteristics and intra-stream dispersal processes exert strong control over maintaining microbial mat coverage, biomass accrual, and diatom species composition.

}, keywords = {LTER-MCM, Antarctica, diatom, microbial mat, streams, transplant, turnover}, url = {https://www.proquest.com/docview/2634590982}, author = {Darling, Joshua P.}, editor = {Diane M. McKnight} } @article {4586, title = {Diatoms in hyporheic sediments trace organic matter retention and processing in the McMurdo Dry Valleys, Antarctica}, journal = {Journal of Geophysical Research: Biogeosciences}, volume = {126}, year = {2021}, month = {02/2021}, pages = {e2020JG006097}, abstract = {

In low-nutrient streams in cold and arid ecosystems, the spiraling of autochthonous particulate organic matter (POM) may provide important nutrient subsidies downstream. Because of its lability and the spatial heterogeneity of processing in hyporheic sediments, the downstream transport and fate of autochthonous POM can be difficult to trace. In Antarctic McMurdo Dry Valley (MDV) streams, any POM retained in the hyporheic zone is expected to be derived from surface microbial mats that contain diatoms with long-lasting silica frustules. We tested whether diatom frustules can be used to trace the retention of autochthonous POM in the hyporheic zone and whether certain geomorphic locations promote this process. The accumulation of diatom frustules in hyporheic sediments, measured as biogenic silica, was correlated with loss-on-ignition organic matter and sorbed ammonium, suggesting that diatoms can be used to identify locations where POM has been retained and processed over long timescales, regardless of whether the POM remains intact. In addition, by modeling the upstream sources of hyporheic diatom assemblages, we found that POM was predominantly derived from N-fixing microbial mats of the genus Nostoc. In terms of spatial variability, we conclude that the hyporheic sediments adjacent to the stream channel that are regularly inundated by daily flood pulses are where the most POM has been retained over long timescales. Autochthonous POM is retained in hyporheic zones of low-nutrient streams beyond the MDVs, and we suggest that biogenic silica and diatom composition can be used to identify locations where this transfer is most prevalent.

}, keywords = {LTER-MCM, benthic processes, biogenic silica, biogeochemical cycles processes and modeling, carbon cycling, diatoms, groundwater/surface water interactions, hyporheic zone, McMurdo Dry Valleys, nitrogen cycling, particulate organic matter}, doi = {10.1029/2020JG006097}, url = {https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JG006097}, author = {Heindel, Ruth C and Darling, Joshua P. and Singley, Joel G. and Bergstrom, Anna J. and Diane M. McKnight and Lukkari, Braeden M. and Kathleen A. Welch and Michael N. Gooseff} } @article {4644, title = {From the Heroic Age to today: What diatoms from Shackleton{\textquoteright}s Nimrod expedition can tell us about the ecological trajectory of Antarctic ponds}, journal = {Limnology and Oceanography Letters}, year = {2021}, month = {07/2021}, abstract = {

Biological invasion and environmental change pose major threats to ecosystems. While long-term ecological change is commonly evaluated through sediment cores in lakes, it is generally not feasible for smaller ponds, and spatial resolution is limited. Here, we analyze pond diatom communities collected during Shackleton\&$\#$39;s Nimrod expedition at Cape Royds, Antarctica, to compare with the same waterbodies a century later. We find historical samples to be almost identical to modern counterparts, and provide no evidence of exotic introductions despite increasing human activity. However, a shift occurred in the pond nearest Shackleton\&$\#$39;s hut, Pony Lake, which was dominated by Luticola muticopsis a century ago, and was replaced by Craspedostauros laevissimus. Both are endemic species previously and currently present at Cape Royds, and we hypothesize that a shift in conductivity accompanying changing precipitation patterns may be responsible. Collectively, these results provide important data for assessing human and climate impacts among Antarctic lacustrine habitats.

}, keywords = {LTER-MCM}, issn = {2378-2242}, doi = {10.1002/lol2.10200}, url = {https://aslopubs.onlinelibrary.wiley.com/doi/10.1002/lol2.10200}, author = {Tyler J. Kohler and Howkins, Adrian and Eric R. Sokol and Kopalov{\'a}, Kate{\v r}ina and Cox, Aneliya and Darling, Joshua P. and Michael N. Gooseff and Diane M. McKnight} } @article {4577, title = {Geochemistry of contrasting stream types, Taylor Valley, Antarctica}, journal = {GSA Bulletin}, volume = {133}, year = {2021}, month = {01/2021}, pages = {425-448}, abstract = {

The McMurdo Dry Valley region is the largest ice-free area of Antarctica. Ephemeral streams flow here during the austral summer, transporting glacial meltwater to perennially ice-covered, closed basin lakes. The chemistry of 24 Taylor Valley streams was examined over the two-decade period of monitoring from 1993 to 2014, and the geochemical behavior of two streams of contrasting physical and biological character was monitored across the seven weeks of the 2010\–2011 flow season. Four species dominate stream solute budgets: HCO3\–, Ca2+, Na+, and Cl\–, with SO42\–, Mg2+, and K+ present in significantly lesser proportions. All streams contain dissolved silica at low concentrations. Across Taylor Valley, streams are characterized by their consistent anionic geochemical fingerprint of HCO3 \> Cl \> SO4, but there is a split in cation composition between 14 streams with Ca \> Na \> Mg \> K and 10 streams with Na \> Ca \> Mg \> K.


Andersen Creek is a first-order proglacial stream representative of the 13 short streams that flow \<1.5 km from source to gage. Von Guerard is representative of 11 long streams 2\–7 km in length characterized by extensive hyporheic zones. Both streams exhibit a strong daily cycle for solute load, temperature, dissolved oxygen, and pH, which vary in proportion to discharge. A well-expressed diurnal co-variation of pH with dissolved oxygen is observed for both streams that reflects different types of biological control. The relative consistency of Von Guerard composition over the summer flow season reflects chemostatic regulation, where water in transient storage introduced during times of high streamflow has an extended opportunity for water-sediment interaction, silicate mineral dissolution, and pore-water exchange.

}, keywords = {LTER-MCM}, doi = {10.1130/B35479.1}, url = {https://pubs.geoscienceworld.org/gsa/gsabulletin/article/133/1-2/425/587799/Geochemistry-of-contrasting-stream-types-Taylor}, author = {Harmon, Russell S. and Leslie, Deborah L. and W. Berry Lyons and Kathleen A. Welch and Diane M. McKnight} } @article {4626, title = {The role of hyporheic connectivity in determining nitrogen availability: Insights from an intermittent Antarctic stream}, journal = {Journal of Geophysical Research: Biogeosciences}, year = {2021}, month = {04/2022}, abstract = {

Due to widespread manipulation of nitrogen (N), much research has focused on processes controlling the fate of anthropogenic N in streams. Yet, in a variety of oligotrophic systems, N fixed by periphyton is a significant driver of ecosystem metabolism. Due to difficulties partitioning allochthonous and autochthonous sources, there is limited information regarding how the latter is processed. Autochthonous N may be particularly important in alpine, arid, or polar environments. We test the hypothesis that the availability of remineralized autochthonous N is controlled by connectivity between the hyporheic zone and main channel due to the contrasting biogeochemical functions of benthic autotrophs (including N-fixing Nostoc) and hyporheic heterotrophs in an intermittent Antarctic stream. There, we collected surface water and hyporheic water concurrently at 4-6 hour intervals over a 32.5-hr period during one flow season and opportunistically throughout a second. Hyporheic water had 7 to 30 times greater nitrate-N concentrations relative to surface water across all flow conditions. In contrast, ammonium concentrations were generally lower, although similar among locations. Additionally, nitrate in hyporheic water was positively correlated with silica, an indicator of hyporheic residence time. A laboratory assay confirmed prior inferences that hyporheic microbial communities possess the functional potential to perform nitrification. Together, these findings suggest that remineralized autochthonous N accumulates in the hyporheic zone even as streamflow varies and likely subsidizes stream N availability\—which supports prior inferences from N stable isotope data at this site. These results highlight the importance of hyporheic connectivity in controlling autochthonous N cycling and availability in streams.

}, keywords = {LTER-MCM, Antarctica, autochthonous nitrogen, hyporheic zone, nitrogen cycling, streamflow}, issn = {2169-8953}, doi = {10.1029/2021JG006309}, url = {https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JG006309}, author = {Singley, Joel G. and Gooseff, Michael N. and Diane M. McKnight and Eve-Lyn S. Hinckley} } @article {4648, title = {Supporting simultaneous air revitalization and thermal control in a crewed habitat with temperate Chlorella vulgaris and eurythermic Antarctic Chlorophyta}, journal = {Frontiers in Microbiology}, volume = {12}, year = {2021}, month = {08/2021}, pages = {709746}, abstract = {

Including a multifunctional, bioregenerative algal photobioreactor for simultaneous air revitalization and thermal control may aid in carbon loop closure for long-duration surface habitats. However, using water-based algal media as a cabin heat sink may expose the contained culture to a dynamic, low temperature environment. Including psychrotolerant microalgae, native to these temperature regimes, in the photobioreactor may contribute to system stability. This paper assesses the impact of a cycled temperature environment, reflective of spacecraft thermal loops, to the oxygen provision capability of temperate Chlorella vulgaris and eurythermic Antarctic Chlorophyta. The tested 28-min temperature cycles reflected the internal thermal control loops of the International Space Station (C. vulgaris, 9\–27\°C; Chlorophyta-Ant, 4\–14\°C) and included a constant temperature control (10\°C). Both sample types of the cycled temperature condition concluded with increased oxygen production rates (C. vulgaris; initial: 0.013 mgO2 L-1, final: 3.15 mgO2 L\–1 and Chlorophyta-Ant; initial: 0.653 mgO2 L\–1, final: 1.03 mgO2 L\–1) and culture growth, suggesting environmental acclimation. Antarctic sample conditions exhibited increases or sustainment of oxygen production rates normalized by biomass dry weight, while both C. vulgaris sample conditions decreased oxygen production per biomass. However, even with the temperature-induced reduction, cycled temperature C. vulgaris had a significantly higher normalized oxygen production rate than Antarctic Chlorophyta. Chlorophyll fluorometry measurements showed that the cycled temperature conditions did not overly stress both sample types (FV/FM: 0.6\–0.75), but the Antarctic Chlorophyta sample had significantly higher fluorometry readings than its C. vulgaris counterpart (F = 6.26, P \< 0.05). The steady state C. vulgaris condition had significantly lower fluorometry readings than all other conditions (FV/FM: 0.34), suggesting a stressed culture. This study compares the results to similar experiments conducted in steady state or diurnally cycled temperature conditions. Recommendations for surface system implementation are based off the presented results. The preliminary findings imply that both C. vulgaris and Antarctic Chlorophyta can withstand the dynamic temperature environment reflective of a thermal control loop and these data can be used for future design models.

}, keywords = {LTER-MCM, air revitalization, Antarctica, bioregenerative life support systems, Chlorophyta, McMurdo Dry Valleys, thermal control}, doi = {10.3389/fmicb.2021.709746}, url = {https://www.frontiersin.org/article/10.3389/fmicb.2021.709746}, author = {Matula, Emily E. and Nabity, James A. and Diane M. McKnight} } @phdthesis {4587, title = {Characterization of spatial and environmental influences on stream diatoms and cyanobacteria}, volume = {Ph.D.}, year = {2020}, month = {2020}, school = {University of Colorado Boulder}, type = {doctoral}, address = {Boulder, CO}, abstract = {

Primary producing algae form the basis of carbon fixation, oxygen production, and food webs in aquatic ecosystems globally. However, human activities disrupt climate and freshwater physicochemistry. These impacts alter the health of algal communities and the ecosystem services algae provide. Meanwhile, spatial processes like dispersal and landscape characteristics like geology also influence algal structure and function. Diatoms are indicators of stream health and are model organisms for understanding the processes underlying microbial biogeography. Benthic cyanobacteria present risks to human health through the proliferation of toxin-producing blooms. With this dissertation, I investigate the ecosystem processes that influence diatom and cyanobacterial community composition and taxon distributions. My goal is to advance the understanding of ecosystem controls on algal biogeography and to characterize taxon-specific autecology for use in environmental management. First, I measured the extent of wind-mediated dispersal of benthic diatoms across aquatic habitats to better understand how community composition is structured by spatial processes across the McMurdo Dry Valleys polar desert in Antarctica. I found that inter-habitat dispersal is common but less influential on community composition than intra-habitat factors such as environmental conditions. I then used non-linear, multivariable modeling to assess the relative influences of climate, watershed characteristics, and in-stream stressors on the relative abundances of 268 diatom taxa across gradients of human impact in the northeast United States. My results indicate diatom taxa are affected by different suites of environmental conditions but that taxa belong to ecological guilds based on shared responsiveness to environmental factors. Finally, I applied multivariable modeling towards understanding the effects of aquatic stressors, including herbicides and persistent organic pollutants, on the distributions of benthic cyanobacteria across northeast U.S. streams. I found that watershed characteristics, streamflow, and herbicides were more influential than light availability, water temperature, and nutrients on the distributions of potentially toxigenic cyanobacterial genera. Collectively, this research expands the knowledge of how benthic algal communities and taxon distributions are structured at large spatial scales along gradients of unimpacted and human-altered environmental conditions. I provide a novel modeling framework and taxon-specific autecological information that can be applied to environmental assessments of stream health and future algal research.

}, keywords = {LTER-MCM, algae, dispersal, environmental assessment, human disturbance, metacommunity ecology, species distribution models}, url = {https://www.proquest.com/docview/2476216263}, author = {Schulte, Nicholas O. and Diane M. McKnight} } @article {4515, title = {Evaluating alternative metacommunity hypotheses for diatoms in the McMurdo Dry Valleys using simulations and remote sensing data}, journal = {Frontiers in Ecology and Evolution}, volume = {8}, year = {2020}, month = {09/2020}, abstract = {

Diatoms are diverse and widespread freshwater Eukaryotes that make excellent microbial subjects for addressing questions in metacommunity ecology. In the McMurdo Dry Valleys of Antarctica, the simple trophic structure of glacier-fed streams provides an ideal outdoor laboratory where well-described diatom assemblages are found within two cyanobacterial mat types, which occupy different habitats and vary in coverage within and among streams. Specifically, black mats of Nostoc spp. occur in marginal wetted habitats, and orange mats (Oscillatoria spp. and Phormidium spp.) occur in areas of consistent stream flow. Despite their importance as bioindicators for changing environmental conditions, the role of dispersal in structuring dry valley diatom metacommunities remains unclear. Here, we use MCSim, a spatially explicit metacommunity simulation package for R, to test alternative hypotheses about the roles of dispersal and species sorting in maintaining the biodiversity of diatom assemblages residing in black and orange mats. The spatial distribution and patchiness of cyanobacterial mat habitats was characterized by remote imagery of the Lake Fryxell sub-catchment in Taylor Valley. The available species pool for diatom metacommunity simulation scenarios was informed by the Antarctic Freshwater Diatoms Database, maintained by the McMurdo Dry Valleys Long Term Ecological Research program. We used simulation outcomes to test the plausibility of alternative community assembly hypotheses to explain empirically observed patterns of freshwater diatom biodiversity in the long-term record. The most plausible simulation scenarios suggest species sorting by environmental filters, alone, was not sufficient to maintain biodiversity in the Fryxell Basin diatom metacommunity. The most plausible scenarios included either (1) neutral models with different immigration rates for diatoms in orange and black mats or (2) species sorting by a relatively weak environmental filter, such that dispersal dynamics also influenced diatom community assembly, but there was not such a strong disparity\ in immigration rates between mat types. The results point to the importance of dispersal for understanding current and future biodiversity patterns for diatoms in this ecosystem, and more generally, provide further evidence that metacommunity theory is a useful framework for testing hypotheses about microbial community assembly.

}, keywords = {LTER-MCM, Antarctica, Bacillariophyceae, dispersal, Nostoc, stream ecology}, doi = {10.3389/fevo.2020.521668}, url = {https://www.frontiersin.org/article/10.3389/fevo.2020.521668/full}, author = {Eric R. Sokol and John E. Barrett and Tyler J. Kohler and Diane M. McKnight and Salvatore, Mark R. and Lee F. Stanish} } @article {4471, title = {Geochemistry of aeolian material from the McMurdo Dry Valleys, Antarctica: Insights into Southern Hemisphere dust sources}, journal = {Earth and Planetary Science Letters}, volume = {547}, year = {2020}, month = {10/2020}, abstract = {

In the Southern Hemisphere, the major sources of dust and other aeolian materials are from Patagonia, South Africa, Australia, and New Zealand. Dust from Patagonia and New Zealand has been identified in ice cores throughout Antarctica, suggesting that during arid and windy periods, such as glacial periods, dust can be entrained and transported onto the continent. However, little information exists on modern Antarctic dust sources, transport, and its role in the Southern Hemisphere dust cycle. We present the first geochemical characterization of aeolian materials collected at five heights (between 5 cm and 100 cm) above the surface in four valleys within the McMurdo Dry Valleys, the largest ice-free area in Antarctica. Our mineralogy data indicate that these materials are primarily derived from local rocks of the McMurdo Volcanics, Ferrar Dolerite, Beacon Sandstone and Granite Harbor Intrusives, with varying contributions of each rock type dependent on the valley location. While major oxide, trace element and rare earth element data show that low elevation and coastal locations (with respect to the Ross Sea) are dominated by local sources, high elevation and inland locations have accumulated both local materials and dust from other distant Southern Hemisphere sources. This far-traveled material may not be accumulating today, but represents a paleo source that is resuspended from the soils. By geochemically \“fingerprinting\” aeolian materials from the MDV, we can better inform future studies on the transport of materials within Antarctica and between Southern Hemisphere land masses.

}, keywords = {LTER-MCM, aeolian material, Antarctica, major oxides, mineralogy, rare earth elements, trace elements}, doi = {10.1016/j.epsl.2020.116460}, url = {https://www.sciencedirect.com/science/article/pii/S0012821X20304040}, author = {Melisa A. Diaz and Welch, Susan A. and Sheets, J. M. and Kathleen A. Welch and Khan, Alia L. and Byron Adams and Diane M. McKnight and Craig S Cary and W. Berry Lyons} } @article {4463, title = {Silicon isotopes reveal a non-glacial source of silicon to Crescent Stream, McMurdo Dry Valleys, Antarctica}, journal = {Frontiers in Earth Science}, volume = {8}, year = {2020}, month = {06/2020}, abstract = {

In high latitude environments, silicon is supplied to river waters by both glacial and non-glacial chemical weathering. The signal of these two end-members is often obscured by biological uptake and/or groundwater input in the river catchment. McMurdo Dry Valleys streams in Antarctica have no deep groundwater input, no connectivity between streams and no surface vegetation cover, and thus provide a simplified system for us to constrain the supply of dissolved silicon (DSi) to rivers from chemical weathering in a glacial environment. Here we report dissolved Si concentrations, germanium/silicon ratios (Ge/Si) and silicon isotope compositions (δ30SiDSi) in Crescent Stream, McMurdo Dry Valleys for samples collected between December and February in the 2014\−2015, 2015\−2016, and 2016\−2017 austral seasons. The δ30SiDSi compositions and DSi concentrations are higher than values reported in wet-based glacial meltwaters, and form a narrow cluster within the range of values reported for permafrost dominated Arctic Rivers. High\ δ30SiDSi\ compositions, ranging from +0.90\‰ to +1.39\‰, are attributed to (i) the precipitation of amorphous silica during freezing of waters in isolated pockets of the hyporheic zone in the winter and the release of Si from unfrozen pockets during meltwater-hyporheic zone exchange in the austral summer, and (ii) additional Si isotope fractionation via long-term Si uptake in clay minerals and seasonal Si uptake into diatoms superimposed on this winter-derived isotope signal. There is no relationship between\ δ30SiDSi\ compositions and DSi concentrations with seasonal and daily discharge, showing that stream waters contain DSi that is in equilibrium with the formation of secondary Si minerals in the hyporheic zone. We show that\ δ30SiDSi\ compositions can be used as tracers of silicate weathering in the hyporheic zone and possible tracers of freeze-thaw conditions in the hyporheic zone. This is important in the context of the ongoing warming in McMurdo Dry Valleys and the supply of more meltwaters to the hyporheic zone of McMurdo Dry Valley streams.

}, keywords = {LTER-MCM}, doi = {10.3389/feart.2020.00229}, url = {https://www.frontiersin.org/articles/10.3389/feart.2020.00229/full}, author = {Hirst, Catherine and Opfergelt, Sophie and Fran{\c c}ois Gaspard and Hendry, Katharine R. and Hatton, Jade E. and Sue Welch and Diane M. McKnight and W. Berry Lyons} } @article {4466, title = {Silicon isotopic composition of dry and wet-based glaciers in Antarctica}, journal = {Frontiers in Earth Science}, volume = {8}, year = {2020}, month = {07/2020}, abstract = {

Glaciers and ice sheets export significant amounts of silicon (Si) to downstream ecosystems, impacting local and potentially global biogeochemical cycles. Recent studies have shown Si in Arctic glacial meltwaters to have an isotopically distinct signature when compared to non-glacial rivers. This is likely linked to subglacial weathering processes and mechanochemical reactions. However, there are currently no silicon isotope (δ30Si) data available from meltwater streams in Antarctica, limiting the current inferences on global glacial silicon isotopic composition and its drivers. To address this gap, we present dissolved silicon (DSi), δ30SiDSi, and major ion data from meltwater streams draining a polythermal glacier in the region of the West Antarctic Peninsula (WAP; King George Island) and a cold-based glacier in East Antarctica [Commonwealth Stream, McMurdo Dry Valleys (MDV)]. These data, alongside other global datasets, improve our understanding of how contrasting glacier thermal regime can impact upon Si cycling and therefore the δ30SiDSi composition. We find a similar δ30SiDSi composition between the two sites, with the streams on King George Island varying between -0.23 and +1.23\‰ and the Commonwealth stream varying from -0.40 to +1.14\‰. However, meltwater streams in King George Island have higher DSi concentrations, and the two glacial systems exhibit opposite DSi \– δ30SiDSi trends. These contrasts likely result from differences in weathering processes, specifically the role of subglacial processes (King George Island) and, supraglacial processes followed by in-stream weathering in hyporheic zones (Commonwealth Stream). These findings are important when considering likely changes in nutrient fluxes from Antarctic glaciers under climatic warming scenarios and consequent shifts in glacial thermal regimes.

}, keywords = {LTER-MCM}, doi = {10.3389/feart.2020.00286}, url = {https://www.frontiersin.org/articles/10.3389/feart.2020.00286/full}, author = {Hatton, Jade E. and Hendry, Katharine R. and Hirst, Catherine and Opfergelt, Sophie and Henkel, Susann and Silva-Busso, Adri{\'a}n and Welch, Susan A. and Wadham, Jemma L. and W. Berry Lyons and Bagshaw, Elizabeth and Staubwasser, Michael and Diane M. McKnight} } @article {4244, title = {Diurnal chemistry of two contrasting stream types, Taylor Valley, McMurdo Dry Valley Region, Antarctica}, journal = {E3S Web of Conferences}, volume = {98}, year = {2019}, month = {06/2019}, abstract = {

Numerous ephemeral streams flow within the McMurdo Dry Valley Region of Antarctica that transport glacial meltwater to perennially ice-covered, closed-basin lakes during the austral summer. The diurnal behavior for two Taylor Valley streams of different character was examined during the summer of 2010-11. Andersen Creek is a short, 1st-order proglacial stream, whereas Von Guerard Stream is a long, high-order stream with an extensive hyporheic zone that has a substantial cyanobacterial algal mat community in its middle reaches. Both streams display strong daily cycles for temperature, electrical conductivity, dissolved oxygen, and pH. Conductivity varies in concert with flow, with solute dilution occurring during the daily high-flow pulse. Dissolved oxygen co-varies strongly with pH at Andersen Creek but not for Von Guerard Stream. Each stream has a distinct geochemical character that for Andersen Creek is a direct reflection of its glacial source, unmodified by secondary effects, whereas that for Von Guerard Stream is modulated by its resident algal mat community and through extensive hyporheic zone interaction and exchange.

}, keywords = {LTER-MCM}, doi = {10.1051/e3sconf/20199801020}, url = {https://www.e3s-conferences.org/articles/e3sconf/abs/2019/24/e3sconf_wri-162018_01020/e3sconf_wri-162018_01020.html}, author = {Harmon, Mark E. and Leslie, D.L. and W. Berry Lyons and Kathleen A. Welch and Diane M. McKnight}, editor = {Chudaev, O. and Kharaka, Y. and Harmon, R.S. and Millot, R. and Shouakar-Stash, O.} } @article {4373, title = {The hydroecology of an ephemeral wetland in the McMurdo Dry Valleys, Antarctica}, journal = {Journal of Geophysical Research: Biogeosciences}, year = {2019}, month = {11/2019}, abstract = {

The McMurdo Dry Valleys (MDV) is a polar desert on the coast of East Antarctica where ephemeral wetlands become hydrologically active during warm and sunny summers when sub-surface flows are generated from melting snowfields. To understand the structure and function of polar wetland ecosystems, we investigated the hydroecology of one such wetland, the Wormherder Creek wetland, during the warm and sunny summer of 2008 \– 2009, when the wetland was hydrologically reactivated. Conservative tracer (LiCl) was injected for a 2-hour period into a stream above the wetland to determine flow path orientations and hydrologic residence times. Tracer results indicated that surface water is rapidly exchanged with wetland groundwater and wetland residence times may exceed two austral summers. Major ion concentrations were uniform in samples from surface water and shallow groundwater throughout the wetland. Microbial mats in the wetland had high autotrophic index values (the ratios of chlorophyll a [Chl-a]/ash-free dry mass [AFDM]), ranging from 9-38 μg Chl-a/mg AFDM, indicative of actively photosynthesizing mat communities. The diatom communities in the mats were relatively uniform compared to those in mats from regularly flowing MDV streams, with four endemic and one widespread diatom taxa of the genus Luticola accounting for an average of 86\% of the community. These results indicate that the hydrologic characteristics of the wetland contribute to uniform geochemical conditions. In turn, uniform geochemical conditions may explain the high autotrophic index values of the microbial mats and relatively low spatial variation of the diatom community.

}, keywords = {LTER-MCM, Antarctica, desert hydrology, diatom biodiversity, hyporheic interactions, wetlands}, doi = {10.1029/2019JG005153}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019JG005153}, author = {Wlostowski, Adam and Schulte, Nicholas O. and Byron Adams and Ball, Becky and Rhea M.M. Esposito and Michael N. Gooseff and W. Berry Lyons and Uffe N. Nielsen and Ross A. Virginia and Diana H. Wall and Kathleen A. Welch and Diane M. McKnight} } @article {4335, title = {Sabbea gen. nov., a new diatom genus (Bacillariophyta) from continental Antarctica}, journal = {Phytotaxa}, volume = {418}, year = {2019}, month = {09/2019}, abstract = {

The non-marine diatom flora of the Antarctic Continent includes several endemic taxa recorded over the past 100 years. One of these taxa, Navicula adminensis D.Roberts \& McMinn, was described from the Vestfold Hills, East Antarctica. Detailed light and scanning electron microscopy observations have shown that based on its morphological features, the species does not belong to the genus Navicula sensu stricto. To determine the most closely related genera to N. adminensis, the morpho- logical features of Adlafia, Kobayasiella, Envekadea, Stenoneis, Berkeleya, Climaconeis, and Parlibellus were compared with those of N. adminensis. Although each of these genera shows one or more similar features, none of them accommodates the salient morphological characteristics of N. adminensis. Therefore, a new genus, Sabbea gen. nov., is herein described, and Navicula adminensis is formally transferred to the new genus as Sabbea adminensis comb. nov. The genus Sabbea is characterized by uniseriate striae composed of small, rounded areolae occluded externally by individual hymenes, a rather simple raphe structure with straight, short proximal ends and short terminal raphe fissures, open girdle bands with double perforation and a very shallow mantle.

}, keywords = {LTER-MCM, Bacillariophyta, Cape Royds, East Antarctica, McMurdo Dry Valleys, new genus, Vestfold Hills}, doi = {10.11646/phytotaxa.418.1.2}, url = {https://www.mapress.com/j/pt/article/view/phytotaxa.418.1.2}, author = {Bishop, Jordan and Kopalov{\'a}, Kate{\v r}ina and Darling, Joshua P. and Schulte, Nicholas O. and Tyler J. Kohler and McMinn, Andrew and Sarah A. Spaulding and Diane M. McKnight and Bart Van de Vijver} } @article {4156, title = {Aeolian material transport and its role in landscape connectivity in the McMurdo Dry Valleys, Antarctica}, journal = {Journal of Geophysical Research: Earth Surface}, volume = {123}, year = {2018}, month = {12/2018}, pages = {3323 - 3337}, abstract = {

Arid regions, particularly polar and alpine desert environments, have diminished landscape connectivity compared to temperate regions due to limited and/or seasonal hydrological processes. For these environments, aeolian processes play a particularly important role in landscape evolution and biotic community vitality through nutrient and solute additions. The McMurdo Dry Valleys (MDV) are the largest ice-free area in Antarctica and are potentially a major source of aeolian material for the continent. From this region, samples were collected at five heights (~5, 10, 20, 50, and 100 cm) above the surface seasonally for 2013 through 2015 from Alatna Valley, Victoria Valley, Miers Valley, and Taylor Valley (Taylor Glacier, East Lake Bonney, F6 (Lake Fryxell), and Explorer\’s Cove). Despite significant geological separation and varying glacial histories, low-elevation and coastal sites had similar major ion chemistries, as did high-elevation and inland locations. This locational clustering of compositions was also evident in scanning electron microscopy images and principal component analyses, particularly for samples collected at ~100 cm above the surface. Compared to published soil literature, aeolian material in Taylor Valley demonstrates a primarily down-valley transport of material toward the coast. Soluble N:P ratios in the aeolian material reflect relative nutrient enrichments seen in MDV soils and lakes, where younger, coastal soils are relatively N depleted, while older, up-valley soils are relatively P depleted. The aeolian transport of materials, including water-soluble nutrients, is an important vector of connectivity within the MDV and provides a mechanism to help \“homogenize\” the geochemistry of both soil and aquatic ecosystems.

}, keywords = {LTER-MCM}, doi = {10.1029/2017JF004589}, url = {https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2017JF004589}, author = {Melisa A. Diaz and Byron Adams and Kathleen A. Welch and Sue Welch and Opiyo, Stephen O. and Khan, Alia L. and Diane M. McKnight and Craig S Cary and W. Berry Lyons} } @phdthesis {4189, title = {Biogeochemistry, contaminant transport, and atmospheric exchange in glacial cryoconite meltwater of the McMurdo Dry Valleys, Antarctica}, volume = {Ph.D.}, year = {2018}, month = {2018}, pages = {245}, school = {University of Colorado}, type = {doctoral}, address = {Boulder, CO}, abstract = {

Polar regions serve as a global sink for many forms of semi-volatile pollution emitted from low- or midlatitudes of the populated world. This study examined the longrange atmospheric transport, fate, and phase partitioning of semi-volatile organic contaminants from air masses into meltwater and aeolian sediment on six glaciers in the McMurdo Dry Valleys of Antarctica. A novel low-cost, field-portable instrument was developed for the in-situ solid-phase extraction of trace contaminants in extreme environmental conditions without access to electricity or traditional laboratory facilities. Beyond polar research, this equipment is applicable for rapid field extraction and stabilization of samples assessing air and water quality after natural disasters. This is the first published study to identify the presence of anthropogenic perfluorinated compounds in the Transantarctic Mountain region and indicates a longer range of poleward contaminant transport than prior estimates in the Southern Hemisphere. Additional research examined the biochemistry and climatic variability of open and sealed cryoconite holes on glacial surfaces throughout the initial melt, equilibrium, and refreezing periods in 2013\–2015. High solute concentrations relative to glacial ice indicate that the pools can remain isolated from hydrologic connectivity for more than a decade. Microbial carbon cycling in pools enclosed by ice led to atmospheric disequilibrium and extreme pH. Analysis of unique air, liquid, and ice stratification in cryoconite holes revealed vertical patterns representing a highly accurate, multi-year record of past weather conditions sensitive enough to identify individual dates. This research identifies fluctuations in atmospheric contaminant transport, specific timeframes for deposition events, and may be used in back-trajectory models to help identify the source and variability of semi-volatile emissions in the Southern hemisphere.

}, keywords = {LTER-MCM, Antarctica, applied sciences, contaminant transport, cryoconite, earth sciences, glacier, hydrology, melt}, url = {https://search.proquest.com/docview/2048314678}, author = {Mass, Alex Q. and Diane M. McKnight} } @article {4159, title = {BioTIME: A database of biodiversity time series for the Anthropocene}, journal = {Global Ecology and Biogeography}, volume = {27}, year = {2018}, month = {07/2018}, pages = {760-786}, abstract = {

Motivation: The BioTIME database contains raw data on species identities and abundances in ecological assemblages through time. These data enable users to calculate temporal trends in biodiversity within and amongst assemblages using a broad range of metrics. BioTIME is being developed as a community-led open-source database of biodiversity time series. Our goal is to accelerate and facilitate quantitative analysis of temporal patterns of biodiversity in the Anthropocene.

Main types of variables included: The database contains 8,777,413 species abundance records, from assemblages consistently sampled for a minimum of 2 years, which need not necessarily be consecutive. In addition, the database contains metadata relating to sampling methodology and contextual information about each record.

Spatial location and grain: BioTIME is a global database of 547,161 unique sampling locations spanning the marine, freshwater and terrestrial realms. Grain size varies across datasets from 0.0000000158 km2 (158 cm2) to 100 km2 (1,000,000,000,000 cm2). Time period and grain BioTIME records span from 1874 to 2016. The minimal temporal grain across all datasets in BioTIME is a year.

Major taxa and level of measurement:\ BioTIME includes data from 44,440 species across the plant and animal kingdoms, ranging from plants, plankton and terrestrial invertebrates to small and large vertebrates.

Software format: .csv and .SQL.

}, keywords = {LTER-MCM, biodiversity, global, spatial, species richness, temporal, turnover}, doi = {10.1111/geb.12729}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/geb.12729}, author = {Dornelas, Maria and Ant{\~a}o, Laura H. and Moyes, Faye and Bates, Amanda E. and Magurran, Anne E. and Adam, Du{\v s}an and Akhmetzhanova, Asem A. and Appeltans, Ward and Arcos, Jos{\'e} Manuel and Arnold, Haley and Ayyappan, Narayanan and Badihi, Gal and Baird, Andrew H. and Barbosa, Miguel and Barreto, Tiago Egydio and B{\"a}ssler, Claus and Bellgrove, Alecia and Belmaker, Jonathan and Benedetti-Cecchi, Lisandro and Bett, Brian J. and Bjorkman, Anne D. and B{\l}a{\.z}ewicz, Magdalena and Blowes, Shane A. and Bloch, Christopher P. and Bonebrake, Timothy C. and Boyd, Susan and Bradford, Matt and Brooks, Andrew J. and Brown, James H. and Bruelheide, Helge and Budy, Phaedra and Carvalho, Fernando and Casta{\~n}eda-Moya, Edward and Chen, Chaolun Allen and Chamblee, John F. and Chase, Tory J. and Siegwart Collier, Laura and Collinge, Sharon K. and Condit, Richard and Cooper, Elisabeth J. and Cornelissen, J. Hans C. and Cotano, Unai and Kyle Crow, Shannan and Damasceno, Gabriella and Davies, Claire H. and Davis, Robert A. and Day, Frank P. and Degraer, Steven and Doherty, Tim S. and Dunn, Timothy E. and Durigan, Giselda and Duffy, J. Emmett and Edelist, Dor and Edgar, Graham J. and Elahi, Robin and Elmendorf, Sarah C. and Enemar, Anders and Ernest, S. K. Morgan and Escribano, Rub{\'e}n and Estiarte, Marc and Evans, Brian S. and Fan, Tung-Yung and Turini Farah, Fabiano and Loureiro Fernandes, Luiz and Farneda, F{\'a}bio Z. and Fidelis, Alessandra and Fitt, Robert and Fosaa, Anna Maria and Daher Correa Franco, Geraldo Antonio and Frank, Grace E. and Fraser, William R. and Garc{\'\i}a, Hernando and Cazzolla Gatti, Roberto and Givan, Or and Gorgone-Barbosa, Elizabeth and Gould, William A. and Gries, Corinna and Grossman, Gary D. and Gutierr{\'e}z, Julio R. and Hale, Stephen and Harmon, Mark E. and Harte, John and Haskins, Gary and Henshaw, Donald L. and Hermanutz, Luise and Hidalgo, Pamela and Higuchi, Pedro and Hoey, Andrew and Van Hoey, Gert and Hofgaard, Annika and Holeck, Kristen and Hollister, Robert D. and Holmes, Richard and Hoogenboom, Mia and Hsieh, Chih-hao and Hubbell, Stephen P. and Huettmann, Falk and Huffard, Christine L. and Hurlbert, Allen H. and Macedo Ivanauskas, Nat{\'a}lia and Jan{\'\i}k, David and Jandt, Ute and Ja{\.z}d{\.z}ewska, Anna and Johannessen, Tore and Johnstone, Jill and Jones, Julia and Jones, Faith A. M. and Kang, Jungwon and Kartawijaya, Tasrif and Keeley, Erin C. and Kelt, Douglas A. and Kinnear, Rebecca and Klanderud, Kari and Knutsen, Halvor and Koenig, Christopher C. and Kortz, Alessandra R. and Kr{\'a}l, Kamil and Kuhnz, Linda A. and Kuo, Chao-Yang and Kushner, David J. and Laguionie-Marchais, Claire and Lancaster, Lesley T. and Min Lee, Cheol and Lefcheck, Jonathan S. and L{\'e}vesque, Esther and Lightfoot, David and Lloret, Francisco and Lloyd, John D. and L{\'o}pez-Baucells, Adri{\`a} and Louzao, Maite and Madin, Joshua S. and Magn{\'u}sson, Borg{\th}{\'o}r and Malamud, Shahar and Matthews, Iain and McFarland, Kent P. and McGill, Brian and Diane M. McKnight and McLarney, William O. and Meador, Jason and Meserve, Peter L. and Metcalfe, Daniel J. and Meyer, Christoph F. J. and Michelsen, Anders and Milchakova, Nataliya and Moens, Tom and Moland, Even and Moore, Jon and Mathias Moreira, Carolina and M{\"u}ller, J{\"o}rg and Murphy, Grace and Myers-Smith, Isla H. and Myster, Randall W. and Naumov, Andrew and Neat, Francis and Nelson, James A. and Paul Nelson, Michael and Newton, Stephen F. and Norden, Natalia and Oliver, Jeffrey C. and Olsen, Esben M. and Onipchenko, Vladimir G. and Pabis, Krzysztof and Pabst, Robert J. and Paquette, Alain and Pardede, Sinta and Paterson, David M. and P{\'e}lissier, Rapha{\"e}l and Pe{\~n}uelas, Josep and P{\'e}rez-Matus, Alejandro and Pizarro, Oscar and Pomati, Francesco and Post, Eric and Prins, Herbert H. T. and John C. Priscu and Provoost, Pieter and Prudic, Kathleen L. and Pulliainen, Erkki and Ramesh, B. R. and Mendivil Ramos, Olivia and Rassweiler, Andrew and Rebelo, Jose Eduardo and Reed, Daniel C. and Reich, Peter B. and Remillard, Suzanne M. and Richardson, Anthony J. and Richardson, J. Paul and van Rijn, Itai and Rocha, Ricardo and Rivera-Monroy, Victor H. and Rixen, Christian and Robinson, Kevin P. and Ribeiro Rodrigues, Ricardo and de Cerqueira Rossa-Feres, Denise and Rudstam, Lars and Ruhl, Henry and Ruz, Catalina S. and Sampaio, Erica M. and Rybicki, Nancy and Rypel, Andrew and Sal, Sofia and Salgado, Beatriz and Santos, Flavio A. M. and Savassi-Coutinho, Ana Paula and Scanga, Sara and Schmidt, Jochen and Schooley, Robert and Setiawan, Fakhrizal and Shao, Kwang-Tsao and Shaver, Gaius R. and Sherman, Sally and Sherry, Thomas W. and Sici{\'n}ski, Jacek and Sievers, Caya and da Silva, Ana Carolina and Rodrigues da Silva, Fernando and Silveira, Fabio L. and Slingsby, Jasper and Smart, Tracey and Snell, Sara J. and Soudzilovskaia, Nadejda A. and Souza, Gabriel B. G. and Maluf Souza, Flaviana and Castro Souza, Vin{\'\i}cius and Stallings, Christopher D. and Stanforth, Rowan and Stanley, Emily H. and Mauro Sterza, Jos{\'e} and Stevens, Maarten and Stuart-Smith, Rick and Rondon Suarez, Yzel and Supp, Sarah} } @article {4110, title = {Catch and release: Hyporheic retention and mineralization of N-fixing Nostoc sustains downstream microbial mat biomass in two polar desert streams}, journal = {Limnology and Oceanography Letters}, volume = {3}, year = {2018}, month = {07/2018}, pages = {357 - 364}, abstract = {

Much work has been performed to investigate controls on nitrogen (N) uptake in streams, yet the fate of assimilated N is comparatively poorly resolved. Here, we use in-stream fixed N as an isotopic tracer to study the fate of assimilated N in glacial meltwater streams. We characterized\ d15N signatures of Oscillatorean, Chlorophyte, and N-fixing\ Nostoc\ mats over the lengths of two streams, and transported particulate organic matter (POM) in one. POM was isotopically most similar to\ Nostoc, which always had values near the atmospheric standard, suggesting N-fixation. Other mat types were depleted upstream, and became progressively enriched downstream, indicating a shift in N source. These results collectively show that\ Nostoc-derived N is mobilized, mineralized, and increasingly assimilated downstream as more depleted glacier-derived N is exhausted, demonstrating the importance of organic matter processing to balancing elemental budgets, and improving our understanding of nutrient cycling in lotic environments.

}, keywords = {LTER-MCM}, doi = {10.1002/lol2.10087}, url = {https://aslopubs.onlinelibrary.wiley.com/doi/abs/10.1002/lol2.10087}, author = {Tyler J. Kohler and Lee F. Stanish and Liptzin, D. and John E. Barrett and Diane M. McKnight} } @article {4068, title = {Near-surface refractory black carbon observations in the atmosphere and snow in the McMurdo Dry Valleys, Antarctica and potential impacts of foehn winds}, journal = {Journal of Geophysical Research: Atmospheres}, volume = {123}, year = {2018}, month = {01/2018}, pages = {2877 - 2887}, abstract = {

Measurements of light absorbing particles in the boundary layer of the high southern latitudes are scarce, particularly in the McMurdo Dry Valleys (MDV),\ Antarctica. During the 2013 - 2014 austral summer near-surface boundary layer refractory black carbon (rBC) aerosols were measured in air by a single particle soot photometer (SP2) at multiple locations in the MDV. Near-continuous rBC atmospheric measurements were collected at Lake Hoare Camp (LH) over two months and for several hours at more remote locations away from established field camps. We investigated periods dominated by both up and down-valley winds to explore the causes of differences in rBC concentrations and size distributions. Snow samples were also collected in a 1m pit on a glacier near the camp. The range of concentrations rBC in snow were 0.3 \– 1.2 \± 0.3 μg-rBC/L-H2O, and total organic carbon were 0.3 \– 1.4 \± 0.3 mg/L. The rBC concentrations measured in this snow pit are not sufficient to reduce surface albedo, however, there is potential for accumulation of rBC on snow and ice surfaces at low elevation throughout the MDV which were not measured as part of this study. At LH, the average background rBC mass aerosol concentrations was 1.3 ng/m3. rBC aerosol mass concentrations were slightly lower, 0.09 \– 1.3 ng/m3, at the most remote sites in the MDV. Concentration spikes as high as 200 ng/m3 were observed at LH, associated with local activities. During a foehn wind event, the average rBC mass concentration increased to 30-50 ng m-3. Here we show the rBC increase could be due to resuspension of locally produced BC from generators, rocket toilets, and helicopters, which may remain on the soil surface until redistributed during high wind events. Quantification of local production and long-range atmospheric transport of rBC to the MDV is necessary for understanding the impacts of this species on regional climate.\ 

}, keywords = {LTER-MCM}, doi = {10.1002/2017JD027696}, url = {http://doi.wiley.com/10.1002/2017JD027696}, author = {Khan, Alia L. and McMeeking, Gavin and Schwarz, Joshua P. and Xian, Peng and Kathleen A. Welch and W. Berry Lyons and Diane M. McKnight} } @article {4107, title = {Spatial and temporal patterns of microbial mats and associated invertebrates along an Antarctic stream}, journal = {Polar Biology}, volume = {41}, year = {2018}, month = {10/2018}, pages = {1911{\textendash}1921}, abstract = {

Microbial biofilms are biological hotspots in many alpine and polar ecosystems, but the controls on and functional significance of their fauna are little known. We studied cyanobacterial mats and the underlying sediment in a glacial meltwater stream in the McMurdo Dry Valleys, Antarctica. We investigated mat biomass (total and phototrophic), diatoms, and micro-meiofauna (nematodes, rotifers, and tardigrades) at nine sites along a 1670 m stream reach in a cold, low-flow growing season, and in a warmer growing season in which peak flows (above 100 L s\−1) scoured the mats. Diatom and invertebrate communities were not related, but mat biomass in the low-flow year was negatively related to nematode abundance, including that of the omnivore\ Eudorylaimus. In the high-flow year that followed, invertebrate abundance was reduced in the mats, diatom community structure was altered, and mat biomass was higher. The difference in invertebrate abundance between years was greater in mats in upstream reaches, where the greatest increases in flow velocity may have occurred, and was negligible in mats in downstream reaches as well as in the sediment beneath the mats. Integrating our results with previous findings, we generate two predictive hypotheses to be tested in glacial meltwater streams: (1) under peak flows invertebrates decline in the microbial mats, while (2) the sediment beneath the mats is a refuge from the flow disturbance. Our results also suggest that, under stable flow conditions, microinvertebrate grazers could exert top-down control on microbial mat biomass.

}, keywords = {LTER-MCM, diatoms, Disturbance, Dry valleys, Epilithon, Microfauna, Stream flow}, doi = {10.1007/s00300-018-2331-4}, url = {http://link.springer.com/10.1007/s00300-018-2331-4}, author = {Andriuzzi, Walter S. and Lee F. Stanish and Breana L. Simmons and Chris Jaros and Byron Adams and Diana H. Wall and Diane M. McKnight} } @article {4160, title = {Transit times and rapid chemical equilibrium explain chemostasis in glacial meltwater streams in the McMurdo Dry Valleys, Antarctica}, journal = {Geophysical Research Letters}, volume = {45}, year = {2018}, month = {12/2018}, pages = {13322 - 13331}, abstract = {

Fluid\  transit\  time\  is\  understood\  to\  be\  an\  important\  control\  on\  the\  shape\  of concentration-discharge (C-q) relationships, yet empirical evidence supporting this linkage is limited. We investigated C-q relationships for weathering-derived solutes across seven Antarctic glacial meltwate streams. We hypothesized that (H1) solute fluxes in McMurdo Dry Valley streams are reaction limited so that C-q\ relationships are characterized by dilution and that (H2) transit time explains between-stream variability in the degree of C-q dilution. Results show that C-q relationships are chemostatic because solute equilibrium times are shorter than stream corridor fluid transit times. Between-stream variability in the efficiency of solute production is positively correlated with transit time, suggesting that transit time is an important control on the solute export regime. These results provide empirical evidence for the controls on weathering-derived C-q relationships and have important implications for Antarctic ecosystems and solute export regimes of watersheds worldwide.

}, keywords = {LTER-MCM}, doi = {10.1029/2018GL080369}, url = {https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL080369}, author = {Wlostowski, Adam and Michael N. Gooseff and Diane M. McKnight and W. Berry Lyons} } @article {4022, title = {Decadal ecosystem response to an anomalous melt season in a polar desert in Antarctica}, journal = {Nature Ecology \& Evolution}, volume = {1}, year = {2017}, month = {09/2017}, pages = {1334-1338}, keywords = {LTER-MCM}, doi = {10.1038/s41559-017-0253-0}, url = {https://www.nature.com/articles/s41559-017-0253-0}, author = {Michael N. Gooseff and John E. Barrett and Byron Adams and Peter T. Doran and Andrew G Fountain and W. Berry Lyons and Diane M. McKnight and John C. Priscu and Eric R. Sokol and Cristina D. Takacs-Vesbach and Martijn L. Vandegehuchte and Ross A. Virginia and Diana H. Wall} } @article {4002, title = {Dissolved black carbon in the global cryosphere: Concentrations and chemical signatures}, journal = {Geophysical Research Letters}, volume = {44}, year = {2017}, month = {06/2017}, pages = {6226-6234}, abstract = {

Black carbon (BC) is derived from the incomplete combustion of biomass and fossil fuels and can enhance glacial recession when deposited on snow and ice surfaces. Here we explore the influence of environmental conditions and the proximity to anthropogenic sources on the concentration and composition of dissolved black carbon (DBC), as measured by benzenepolycaroxylic acid (BPCA) markers, across snow, lakes, and streams from the global cryosphere. Data are presented from Antarctica, the Arctic, and high alpine regions of the Himalayas, Rockies, Andes, and Alps. DBC concentrations spanned from 0.62 μg/L to 170 μg/L. The median and (2.5, 97.5) quantiles in the pristine samples were 1.8 μg/L (0.62, 12), and nonpristine samples were 21 μg/L (1.6, 170). DBC is susceptible to photodegradation when exposed to solar radiation. This process leads to a less condensed BPCA signature. In general, DBC across the data set was composed of less polycondensed DBC. However, DBC from the Greenland Ice Sheet (GRIS) had a highly condensed BPCA molecular signature. This could be due to recent deposition of BC from Canadian wildfires. Variation in DBC appears to be driven by a combination of photochemical processing and the source combustion conditions under which the DBC was formed. Overall, DBC was found to persist across the global cryosphere in both pristine and nonpristine snow and surface waters. The high concentration of DBC measured in supraglacial melt on the GRIS suggests that DBC can be mobilized across ice surfaces. This is significant because these processes may jointly exacerbate surface albedo reduction in the cryosphere.\ 

}, keywords = {LTER-MCM}, doi = {10.1002/2017GL073485}, url = {http://doi.wiley.com/10.1002/2017GL073485}, author = {Khan, Alia L. and Wagner, Sasha and Jaff{\'e}, Rudolf and Xian, Peng and Williams, Mark and Armstrong, Richard and Diane M. McKnight} } @article {4064, title = {Freshwater diatom biogeography and the genus Luticola: an extreme case of endemism in Antarctica}, journal = {Polar Biology}, volume = {40}, year = {2017}, month = {03/2017}, pages = {1185-1196}, abstract = {

Historical views have characterized Antarctica as a frozen desert with low diversity, although recent studies suggest that this may not be true for microscopic organisms. For microbes, assessing endemism in the Antarctic region has been particularly important, especially against a backdrop of debate regarding their presumed cosmopolitan nature. To contribute to this conversation, we highlight the observed endemism of the freshwater diatom genus Luti- cola in Antarctica by synthesizing the results of a modern high-resolution taxonomy from the Continental, Maritime, and sub-Antarctic regions. We report that Luticola has one of the highest endemic rates of any diatom genus in Antarctica, in terms of total number of species (taxon endemism) and percentage of the entire genus (phylogenetic endemism). Of the over 200 species of Luticola globally, nearly 20\% (43) occur in the Antarctic, with 42 of these being endemic. Within regions, Maritime Antarctica has the largest number of Luticola species and endemics (28 and 23, respectively), followed by Continental Antarctica (14, 9) and sub-Antarctic islands (8, 6). Thus, 38 of the 42 endemics are found in a single region only. While the timing of Luticola diversi cation has not been established, fossil evidence suggests recent invasions and/or diversi cation over a relatively short geologic timescale. Understanding the origin and evolution of endemic diatom species in Antarctica will help us better understand microbial biogeography, as well as assess and interpret impacts of large-scale environmental change taking place at southern latitudes.

}, keywords = {LTER-MCM}, issn = {0722-4060}, doi = {10.1007/s00300-017-2090-7}, url = {https://link.springer.com/article/10.1007/s00300-017-2090-7}, author = {J. Patrick Kociolek and Kopalova, K and Hamsher, S. E. and Tyler J. Kohler and Bart Van de Vijver and Convey, Peter and Diane M. McKnight} } @article {4023, title = {Hydrologic connectivity and implications for ecosystem processes - Lessons from naked watersheds}, journal = {Geomorphology}, volume = {277}, year = {2017}, month = {01/2017}, pages = {63 - 71}, abstract = {

Hydrologic connectivity has received great attention recently as our conceptual models of watersheds and water quality have evolved in the past several decades. However, the structural complexity of most temperate watersheds (i.e. connections among shallow soils, deep aquifers, the atmosphere and streams) and the dynamic seasonal changes that occur within them (i.e., plant senescence which impacts evapotranspiration) create significant challenges to characterizing or quantifying hydrologic connectivity. The McMurdo Dry Valleys, a polar desert in Antarctica, provide a unique opportunity to study hydrologic connectivity because there is no vegetative cover (and therefore no transpiration), and no deep aquifers connected to surface soils or streams. Glacier melt provides stream flow to well-established channels and closed-basin, ice-covered lakes on the valley floor. Streams are also connected to shallow hyporheic zones along their lengths, which are bounded at ~75 cm depth by ice-cemented permafrost. These hydrologic features and connections provide water for and underpin biological communities. Hence, exchange of water among them provides a vector for exchange of energy and dissolved solutes. Connectivity is dynamic on timescales of a day to a flow season (6\–12 weeks), as streamflow varies over these timescales. The timescales over which these connections occur is also dynamic. Exchanges between streams and hyporheic zones, for example, have been estimated to be as short as hours to as long as several weeks. These exchanges have significant implications for the biogeochemistry of these systems and the biotic communities in each feature. Here we evaluate the lessons we can learn about hydrologic connectivity in the MDV watersheds that are simplified in the context of processes occurring and water reservoirs included in the landscape, yet are sensitive to climate controls and contain substantial physical heterogeneity. We specifically explore several metrics that are simple and/or commonly employed in hydrologic analyses and interpret them in the context of connectivity between and among hydrologic features.

}, keywords = {LTER-MCM}, issn = {0169555X}, doi = {10.1016/j.geomorph.2016.04.024}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0169555X16302483}, author = {Michael N. Gooseff and Wlostowski, Adam and Diane M. McKnight and Chris Jaros} } @article {4018, title = {Thermal autecology describes the occurrence patterns of four benthic diatoms in McMurdo Dry Valley streams}, journal = {Polar Biology}, volume = {40}, year = {2017}, month = {06/2017}, pages = {2381-2396}, abstract = {

Benthic microbial mats in the glacial-fed melt- water streams are hotspots of productivity in the McMurdo Dry Valleys (MDV), Antarctica. Benthic diatoms are common in these mats and the[45 primarily endemic taxa represent the most diverse group of eukaryotes in the MDV. In this harsh polar desert, streams are thermally dynamic with daily water temperatures varying 6\–9 \°C and daily maximum temperatures as high as 15 \°C. Stream temperature may play a role in determining growth rates and survival strategies. To understand taxon-specific adaptations to their environment, we measured the growth rates of unialgal cultures of four diatom taxa (Psammothidium papilio, Hantzschia abundans, Hantzschia amphioxys, and Hantzschia amphioxys f. muelleri) under three temperature conditions (7.6, 10, and 15 \°C) that were representative of maximum daily stream temperatures. We found that P. papilio exhibited a constant growth rate across the full temperature range; this species is most common in streams that begin to flow early in the summer and with less variable thermal regimes. Growth rates for H. abundans were greatest at 15 \°C, but showed a non-linear relationship with temperature. H. amphioxys f. muelleri

grew faster than the other taxa studied and thrived at 10 \°C. Hantzschia amphioxys grew only at the two lower temperatures. These results aligned with the observed relationships between each taxon\’s relative abundance and stream temperatures in the long-term record maintained by the MDV Long-Term Ecological Research program. Overall, our observations suggest that differences in thermal optima may be one factor contributing to and maintaining the diversity of benthic diatom flora in the MDV.
}, keywords = {LTER-MCM}, doi = {10.1007/s00300-017-2151-y}, url = {https://link.springer.com/article/10.1007/s00300-017-2151-y}, author = {Darling, Joshua P. and Garland, Deena D. and Lee F. Stanish and Rhea M.M. Esposito and Eric R. Sokol and Diane M. McKnight} } @article {3917, title = {Dissolved black carbon in Antarctic lakes: chemical signatures of past and present sources}, journal = {Geophysical Research Letters}, year = {2016}, month = {06/2016}, abstract = {

The perennially ice-covered, closed-basin lakes in the McMurdo Dry Valleys, Antarctica, serve as sentinels for understanding the fate of dissolved black carbon from glacial sources in aquatic ecosystems. Here we show that dissolved black carbon can persist in freshwater and saline surface waters for thousands of years, while preserving the chemical signature of the original source materials. The ancient brines of the lake bottom waters have retained dissolved black carbon with a woody chemical signature, representing long-range transport of black carbon from wildfires. In contrast, the surface waters are enriched in contemporary black carbon from fossil fuel combustion. Comparison of samples collected 25\ years apart from the same lake suggests that the enrichment in anthropogenic black carbon is recent. Differences in the chemical composition of dissolved black carbon among the lakes are likely due to biogeochemical processing such as photochemical degradation and sorption on metal oxides.

}, keywords = {LTER-MCM}, doi = {10.1002/2016GL068609}, url = {http://doi.wiley.com/10.1002/2016GL068609}, author = {Khan, Alia L. and Jaff{\'e}, Rudolf and Ding, Yan and Diane M. McKnight} } @article {3714, title = {Evidence for dispersal and habitat controls on pond diatom communities from the McMurdo Sound Region of Antarctica}, journal = {Polar Biology}, year = {2016}, month = {02/2016}, keywords = {LTER-MCM}, issn = {0722-4060}, doi = {10.1007/s00300-016-1901-6}, url = {http://link.springer.com/10.1007/s00300-016-1901-6http://link.springer.com/content/pdf/10.1007/s00300-016-1901-6http://link.springer.com/content/pdf/10.1007/s00300-016-1901-6.pdfhttp://link.springer.com/article/10.1007/s00300-016-1901-6/fulltext.html}, author = {Sakaeva, A. and Eric R. Sokol and Tyler J. Kohler and Lee F. Stanish and Sarah A. Spaulding and Howkins, Adrian and Kathleen A. Welch and W. Berry Lyons and John E. Barrett and Diane M. McKnight} } @article {3951, title = {Hydrological Controls on Ecosystem Dynamics in Lake Fryxell, Antarctica}, journal = {PLOS ONE}, volume = {11}, year = {2016}, month = {07/2016}, pages = {e0159038}, keywords = {LTER-MCM}, doi = {10.1371/journal.pone.015903810.1371}, url = {http://dx.plos.org/10.1371/journal.pone.0159038}, author = {Herbei, Radu and Rytel, Alexander L. and W. Berry Lyons and Diane M. McKnight and Chris Jaros and Michael N. Gooseff and John C. Priscu}, editor = {Hewitt, Judi} } @article {3959, title = {Nutrient treatments alter microbial mat colonization in two glacial meltwater streams from the McMurdo Dry Valleys, Antarctica}, journal = {FEMS Microbiology Ecology}, volume = {92}, year = {2016}, month = {03/2016}, pages = {fiw049}, abstract = {

Microbial mats are abundant in many alpine and polar aquatic ecosystems. With warmer temperatures, new hydrologic pathways are developing in these regions and increasing dissolved nutrient fluxes. In the McMurdo Dry Valleys, thermokarsting may release both nutrients and sediment, and has the potential to influence mats in glacial meltwater streams. To test the role of nutrient inputs on community structure, we created nutrient diffusing substrata (NDS) with agar enriched in N, P and N + P, with controls, and deployed them into two Dry Valley streams. We found N amendments (N and N + P) to have greater chlorophyll-a concentrations, total algal biovolume, more fine filamentous cyanobacteria and a higher proportion of live diatoms than other treatments. Furthermore, N treatments were substantially elevated in Bacteroidetes and the small diatom,\ Fistulifera pelliculosa. On the other hand, species richness was almost double in P and N + P treatments over others, and coccoid green algae and Proteobacteria were more abundant in both streams. Collectively, these data suggest that nutrients have the potential to stimulate growth and alter community structure in glacial meltwater stream microbial mats, and the recent erosion of permafrost and accelerated glacial melt will likely impact resident biota in polar lotic systems here and elsewhere.

}, keywords = {LTER-MCM}, doi = {10.1093/femsec/fiw049}, url = {http://femsec.oxfordjournals.org/lookup/doi/10.1093/femsec/fiw049}, author = {Tyler J. Kohler and David J. Van Horn and Darling, Joshua P. and Cristina D. Takacs-Vesbach and Diane M. McKnight}, editor = {Wagner, Dirk} } @article {3958, title = {Patterns of bacterial biodiversity in the glacial meltwater streams of the McMurdo Dry Valleys, Antarctica}, journal = {FEMS Microbiology Ecology}, volume = {92}, year = {2016}, month = {08/2016}, pages = {fiw148}, abstract = {

Microbial consortia dominate glacial meltwater streams from polar regions, including the McMurdo Dry Valleys (MDV), where they thrive under physiologically stressful conditions. In this study, we examined microbial mat types and sediments found in 12 hydrologically diverse streams to describe the community diversity and composition within and across sites. Sequencing of the 16S rRNA gene from 129 samples revealed \∼24 000 operational taxonomic units (\<97\% DNA similarity), making streams the most biodiverse habitat in the MDV. Principal coordinate analyses revealed significant but weak clustering by mat type across all streams (ANOSIM R-statistic = 0.28) but stronger clustering within streams (ANOSIM R-statistic from 0.28 to 0.94). Significant relationships (P \< 0.05) were found between bacterial diversity and mat ash-free dry mass, suggesting that diversity is related to the hydrologic regimes of the various streams, which are predictive of mat biomass. However, correlations between stream chemistry and community members were weak, possibly reflecting the importance of internal processes and hydrologic conditions. Collectively, these results suggest that localized conditions dictate bacterial community composition of the same mat types and sediments from different streams, and while MDV streams are hotspots of biodiversity in an otherwise depauperate landscape, controls on community structure are complex and site specific.

}, keywords = {LTER-MCM}, doi = {10.1093/femsec/fiw148}, url = {http://femsec.oxfordjournals.org/lookup/doi/10.1093/femsec/fiw148}, author = {David J. Van Horn and Wolf, Caitlin R. and Colman, Daniel R. and Jiang, Xiaoben and Tyler J. Kohler and Diane M. McKnight and Lee F. Stanish and Yazzie, Terrill and Cristina D. Takacs-Vesbach} } @article {3718, title = {Patterns of hydrologic connectivity in the McMurdo dry valleys, Antarctica: a synthesis of 20 years of hydrologic data}, journal = {Hydrological Processes}, volume = {30}, year = {2016}, month = {04/2016}, pages = {2958-2975}, chapter = {2958}, abstract = {

Streams in the McMurdo Dry Valleys (MDVs) of Antarctica moderate an important hydrologic and biogeochemical connection between upland alpine glaciers, valley-bottom soils, and lowland closed-basin lakes. Moreover, MDV streams are simple but dynamic systems ideal for studying interacting hydrologic and ecological dynamics. This work synthesizes 20\ years of hydrologic data, collected as part of the MDVs Long-Term Ecological Research project, to assess spatial and temporal dynamics of hydrologic connectivity between glaciers, streams, and lakes. Long-term records of stream discharge (Q), specific electrical conductance (EC), and water temperature (T) from 18 streams were analysed in order to quantify the magnitude, duration, and frequency of hydrologic connections over daily, annual, and inter-annual timescales. At a daily timescale, we observe predictable diurnal variations in Q, EC, and T. At an annual timescale, we observe longer streams to be more intermittent, warmer, and have higher median EC values, compared to shorter streams. Longer streams also behave chemostatically with respect to EC, whereas shorter streams are more strongly characterized by dilution. Inter-annually, we observe significant variability in annual runoff volumes, likely because of climatic variability over the 20 record years considered. Hydrologic connections at all timescales are vital to stream ecosystem structure and function. This synthesis of hydrologic connectivity in the MDVs provides a useful end-member template for assessing hydrologic connectivity in more structurally complex temperate watersheds.\ 

}, keywords = {LTER-MCM}, doi = {10.1002/hyp.10818}, url = {http://onlinelibrary.wiley.com/doi/10.1002/hyp.10818}, author = {Wlostowski, Adam and Michael N. Gooseff and Diane M. McKnight and Chris Jaros and W. Berry Lyons} } @phdthesis {4098, title = {Quantifying sources, distribution, and processing of light absorbing aerosols in the cryosphere: A comparison of dissolved and refractory black carbon in polar and high mountain regions}, volume = {Ph.D.}, year = {2016}, school = {University of Colorado}, type = {doctoral}, address = {Boulder, CO}, abstract = {

Light absorbing aerosols (LAAs) in snow and ice are one of the least understood parameters in global climate models due to complicated physical processes within the cryosphere and too few\ in situ\ observations. Ground observations are limited due to the difficulty of collecting and preserving samples for analysis from remote environments.
In order to help build a larger repository of ground observations, this dissertation explores the concentration and composition of black carbon (BC) in snow and glacial melt-water across the polar regions in the Arctic and Antarctic, as well as major mountain regions such as the Himalayas, Rockies, and Andes Mountains.

Three state-of-the-art methods for BC detection are applied in this dissertation. The first chapter identifies chemical signatures of past and present sources of dissolved black carbon (DBC) in Antarctic lakes, utilizing a DBC molecular marker method. Here we find that DBC with a woody signature is preserved in the deep, ancient brines of Antarctic lake bottom waters. In contrast, the surface waters are enriched in BC from fossil fuels. The second chapter, which also utilizes the DBC molecular marker

iii\ 

technique, explores DBC across the cryosphere. We show that DBC concentrations are surprisingly high in the bottom waters of Antarctic lakes compared to other remote regions of the cryosphere, even those located near point sources. Aged snow also contains higher DBC concentrations than fresh snow suggesting that dry deposition brings the majority of BC to the cryosphere. Additionally, the DBC composition across samples from the cryosphere are similar due to high amounts of solar exposure leading to photodegradation, except in fresh snow with a wildfire signature. The third and fourth chapters utilize the Single Particle Soot Photometer to measure refractory black carbon (rBC). The third chapter also applies spectral albedo measurements and the light absorption heating method to find that\ coal dust from an active mine in Svalbard, Norway significantly reduces the spectral reflectance of the surrounding Arctic surface snow.\ The fourth chapter reports aerosol rBC concentrations in the boundary layer of the McMurdo Dry Valleys, as well as in snow from the accumulation area of the Commonwealth Glacier. Here we determine that aerosol concentrations increase during high wind events, but there is no significant trend in deposition in the snow pit. This could be due to sporadic deposition during katabatic wind events.

These findings support the importance of real\ in-situ\ observations in order to fully understand the role of BC in the global carbon cycle. It is also evident that local environmental processes can control the concentrations and composition of BC in the cryosphere. These ground-based measurements will likely serve as ground validation for future remote sensing of snow/ice impurities and LAAs deposition models.

}, keywords = {LTER-MCM, applied sciences, black carbon, cryosphere, earth sciences, glacial melt, health and environmental sciences, light absorbing aerosols, polar regions, snow}, url = {https://search.proquest.com/docview/1834518541?accountid=14503}, author = {Khan, Alia L. and Diane M. McKnight} } @article {3875, title = {Stream biogeochemical and suspended sediment responses to permafrost degradation in stream banks in Taylor Valley, Antarctica}, journal = {Biogeosciences}, volume = {13}, year = {2016}, month = {03/2016}, pages = {1723 - 1732}, abstract = {

\ Stream channels in the McMurdo Dry Valleys are characteristically wide, incised, and stable. At typical flows, streams occupy a fraction of the oversized channels, providing habitat for algal mats. In January 2012, we discovered substantial channel erosion and subsurface thermomechanical erosion undercutting banks of the Crescent Stream. We sampled stream water along the impacted reach and compared concentrations of solutes to the long-term data from this stream (\ \∼\  20 years of monitoring). Thermokarst-impacted stream water demonstrated higher electrical conductivity, and concentrations of chloride, sulfate, sodium, and nitrate than the long-term medians. These results suggest that this mode of lateral permafrost degradation may substantially impact stream solute loads and potentially fertilize stream and lake ecosystems. The potential for sediment to scour or bury stream algal mats is yet to be determined, though it may offset impacts of associated increased nutrient loads to streams.

}, keywords = {LTER-MCM}, doi = {10.5194/bg-13-1723-2016}, url = {http://www.biogeosciences.net/13/1723/2016/bg-13-1723-2016.pdf}, author = {Michael N. Gooseff and David J. Van Horn and Sudman, Zachary and Diane M. McKnight and Kathleen A. Welch and W. Berry Lyons} } @article {3306, title = {Antarctic streams as a potential source of iron for the Southern Ocean: Figure 1.}, journal = {Geology}, volume = {43}, year = {2015}, month = {11/2016}, pages = {1003 - 1006}, chapter = {1003}, abstract = {

Due to iron\’s role in oceanic primary production, there has been great interest in quantifying the importance of Fe in regions where concentrations are very low and macronutrients, nitrate and phosphate, are available. Measurements of filterable (i.e., \<0.4 μm) Fe concentrations in streams from Taylor Valley, McMurdo Dry Valleys, Antarctica, suggest that coastal-zone stream Fe input to the Southern Ocean could potentially play an important role in primary production in nearshore regions. Filterable Fe (fFe) data from streams in the McMurdo Dry Valleys were used to represent glacier meltwater that flows through ice-free landscape with the potential of transporting Fe to the Antarctic coastal zone. Estimates of potential fFe flux to the Antarctic Peninsula region using our mean fFe concentration of 10.6 \µg L\–1\ combined with an estimate of ice-free area for the Antarctic Peninsula result in an fFe flux of 1.2 \× 107\ g yr\–1. Although small compared to iceberg and aeolian Fe fluxes, future stream input to the Southern Ocean could increase due to glacier retreat and\ 

}, keywords = {LTER-MCM}, issn = {0091-7613}, doi = {10.1130/G36989.1}, url = {http://geology.gsapubs.org/lookup/doi/10.1130/G36989.1http://geology.geoscienceworld.org/lookup/doi/10.1130/G36989.1}, author = {W. Berry Lyons and Dailey, Kelsey R. and Kathleen A. Welch and Deuerling, Kelly M. and Sue Welch and Diane M. McKnight} } @article {3721, title = { Long-Term Hydrologic Control of Microbial Mat Abundance in McMurdo Dry Valley Streams, Antarctica.}, journal = {Ecosystems}, volume = {18}, year = {2015}, month = {03/2015}, pages = {310-327}, chapter = {310}, abstract = {

Given alterations in global hydrologic regime, we examine the role of hydrology in regulating stream microbial mat abundance in the McMurdo Dry Valleys, Antarctica. Here, perennial mats persist as a desiccated crust until revived by summer streamflow, which varies inter-annually, and has increased since the 1990s. We predicted high flows to scour mats, and intra-seasonal drying to slow growth. Responses were hypothesized to differ based on mat location within streams, along with geomorphology, which may promote (high coverage) or discourage (low coverage) accrual. We compared hydrologic trends with the biomass of green and orange mats, which grow in the channel, and black mats growing at stream margins for 16 diverse stream transects over two decades. We found mat biomass collectively decreased during first decade coinciding with low flows, and increased following elevated discharges. Green mat biomass showed the greatest correlations with hydrology and was stimulated by discharge in high coverage transects, but negatively correlated in low coverage due to habitat scour. In contrast, orange mat biomass was negatively related to flow in high coverage transects, but positively correlated in low coverage because of side-channel expansion. Black mats were weakly correlated with all hydrologic variables regardless of coverage. Lastly, model selection indicated the best combination of predictive hydrologic variables for biomass differed between mat types, but also high and low coverage transects. These results demonstrate the importance of geomorphology and species composition to modeling primary production, and will be useful in predicting ecological responses of benthic habitats to altered hydrologic regimes.

}, keywords = {LTER-MCM}, url = {http://link.springer.com/article/10.1007\%2Fs10021-014-9829-6}, author = {Tyler J. Kohler and Lee F. Stanish and Stenven Crisp and Koch, J. and Liptzin, D. and Baeseman, J. and Diane M. McKnight} } @phdthesis {4087, title = {Physical and chemical controls on the abundance and composition of stream microbial mats from the McMurdo Dry Valleys, Antarctica}, volume = {Ph.D.}, year = {2015}, pages = {272}, school = {University of Colorado}, type = {doctoral}, address = {Boulder, CO}, abstract = {

The McMurdo Dry Valleys of Antarctica are a cold, dry desert, yet perennial microbial mats are abundant in the ephemeral glacial meltwater streams that flow during austral summers. Three types of mats are present (orange, black, and green), and are primarily comprised of filamentous cyanobacteria,\ Nostoc, and chlorophytes, respectively. Mat types furthermore occupy distinct habitats within streams, utilizing the benthos, hyporheic zone, and water column, which expose them to different environmental conditions. Due to a lack of lateral inflows, allochthonous organic inputs, and negligible grazing activity, these streams are ideal for the controlled ecological study of microbial mats. Here, I investigated how mats will respond to physical disturbance, alterations in the hydrologic regime, and nutrient liberation from permafrost melt in the future. Specifically, I: 1) quantified and characterized the regrowth of mat biomass, community structure, and elemental stoichiometry after a scouring disturbance, 2) investigated how geomorphology and taxonomic identity influences the response of mat biomass to hydrologic regime in transects monitored over two decades, and 3) evaluated relationships between water chemistry and the elemental and isotopic composition of mat types over longitudinal and valley-wide gradients in Taylor Valley. I found that mats recovered ~20-50\% of their biomass over the course of an austral summer following scour. Algal communities were significantly different in composition between disturbed and control treatments, but all samples naturally varied in species and elemental stoichiometry over the study period. When the long- term record of mat biomass was compared with hydrologic variables, stream channel mats (orange and green) had the greatest correlations, while marginal mats (black) showed weaker relationships with flow regime. Relationships also differed as a function of stream geomorphology, indicating the importance of substrata and gradient in conjunction with discharge. Lastly, mats showed unique elemental and isotopic compositions. Green and orange mats within the stream channel most reflected water column nutrient concentrations, while black mats showed significant nitrogen fixation. These results highlight the importance of taxonomic identity and habitat to modeling primary production here and elsewhere, and provide insight to how stream microbial mat communities are formed, maintained, and ultimately persist in an isolated polar desert.

}, keywords = {LTER-MCM, algae, Antarctica, biological sciences, climate change, Disturbance, earth sciences, McMurdo Dry Valleys, microbial mats}, url = {https://search.proquest.com/docview/1690497718?accountid=14503}, author = {Tyler J. Kohler}, editor = {Diane M. McKnight} } @article {3712, title = {Potential for real-time understanding of coupled hydrologic and biogeochemical processes in stream ecosystems: Future integration of telemetered data with process models for glacial meltwater streams}, journal = {Water Resources Research}, volume = {51}, year = {2015}, month = {08/2015}, pages = {6725 - 6738}, keywords = {LTER-MCM}, doi = {10.1002/2015WR017618}, url = {http://doi.wiley.com/10.1002/2015WR017618http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002\%2F2015WR017618}, author = {Diane M. McKnight and Cozzetto, K and Cullis, James D.S. and Michael N. Gooseff and Chris Jaros and Koch, J. and W. Berry Lyons and Neupauer, R. M. and Wlostowski, Adam} } @article {3189, title = {Pressure-driven, shoreline currents in a perennially ice-covered, pro-glacial lake in Antarctica, identified from a LiCl tracer injected into a pro-glacial stream}, journal = {Hydrological Processes}, volume = {29}, year = {2015}, month = {05-2015}, pages = {2212 - 2231}, abstract = {

The distribution of streamwater within ice-covered lakes influences sub-ice currents, biological activity and shoreline morphology. Perennially ice-covered lakes in the McMurdo Dry Valleys, Antarctica, provide an excellent natural laboratory to study hydrologic\–limnologic interactions under ice cover. For a 2\ h period on 17 December 2012, we injected a lithium chloride tracer into Andersen Creek, a pro-glacial stream flowing into Lake Hoare. Over 4\ h, we collected 182 water samples from five stream sites and 15 ice boreholes. Geochemical data showed that interflow travelled West of the stream mouth along the shoreline and did not flow towards the lake interior. The chemistry of water from Andersen Creek was similar to the chemistry of water below shoreline ice. Additional evidence for Westward flow included the morphology of channels on the ice surface, the orientation of ripple marks in lake sediments at the stream mouth and equivalent temperatures between Andersen Creek and water below shoreline ice. Streamwater deflected to the right of the mouth of the stream, in the opposite direction predicted by the Coriolis force. Deflection of interflow was probably caused by the diurnal addition of glacial runoff and stream discharge to the Eastern edge of the lake, which created a strong pressure gradient sloping to the West. This flow directed stream momentum away from the lake interior, minimizing the impact of stream momentum on sub-ice currents. It also transported dissolved nutrients and suspended sediments to the shoreline region instead of the lake interior, potentially affecting biological productivity and bedform development.

}, keywords = {LTER-MCM}, doi = {10.1002/hyp.v29.910.1002/hyp.10352}, url = {http://doi.wiley.com/10.1002/hyp.v29.9http://doi.wiley.com/10.1002/hyp.10352}, author = {Castendyk, Devin and Diane M. McKnight and Kathleen A. Welch and Niebuhr, Spencer and Chris Jaros} } @mastersthesis {4084, title = {Quantifying long-term geomorphology of Antarctic streams}, volume = {MS}, year = {2015}, pages = {185}, school = {University of Colorado}, type = {masters}, address = {Boulder, CO}, abstract = {

In 1994, 16 stream transects were established in the McMurdo Dry Valleys of Antarctica beginning a long term data set characterizing microbial communities and channel geometry. The transects were established to record microbial mat dynamics and stream geomorphology. To accomplish this, the transects were surveyed for points of interest outside and inside the stream channel. Beginning in 2010 the microbial surveys received ground based LiDAR support. This allowed for greater resolution in mapping and analyzing stream morphology than traditional surveying methods. The purpose of this study was to overlap the traditional methods of surveying individual points of interest with a data cloud representing the entire stream transect to be able to continue the microbial study into the future unabated. Using surveyed microbial mats as an indicator of a location in time, a history of channel elevations was created for 7 transects. In general, the streams have not changed significantly in the 20 year record, with exceptions being the steep channel of Bohner Stream, and Huey Creek, which receives large sediment loads from the sharply incised upstream channel, both of which saw large variations in maximum bed change exceeding 75cm and 150 cm respectively. In addition to creating an elevation history, relative bed change was plotted against the ash free dry mass of the microbial mats sampled to determine the resilience of the mats. It was found that microbial mats are more abundant in areas of near zero change. The four microbial mats studied however, which include green, black, orange, and red mats, differed greatly in adaptability with regards to bed change. Green microbial mats, which are typically hidden under large immobile rocks, were not often found in areas with any significant bed change. Conversely, orange mats were found in the most dynamic parts of the stream bed with outliers seen in areas with change exceeding 50 cm with. Finally black microbial mats had the largest values of ash free dry mass indicating the largest resilience to the scouring effects of high flow.

}, keywords = {LTER-MCM}, url = {https://search.proquest.com/docview/1727444346?accountid=14503}, author = {Crisp, Steven W.}, editor = {Diane M. McKnight} } @article {3215, title = {Recovery of Antarctic stream epilithon from simulated scouring events}, journal = {Antarctic Science}, volume = {27}, year = {2015}, month = {Jan-08-2015}, pages = {341 - 354}, abstract = {

Microbial mats are common in polar streams and often dominate benthic biomass. Climate change may be enhancing the variability of stream flows in the Antarctic, but so far studies investigating mat responses to disturbance have been limited in this region. Mat regrowth was evaluated following disturbance by experimentally scouring rocks from an ephemeral McMurdo Dry Valley stream over two summers (2001\–02 and 2012\–13). Mats were sampled at the beginning and resampled at the end of the flow season. In 2012\–13, mats were additionally resampled mid-season along with previously undisturbed controls. In 2001\–02 rocks regained 47\% of chlorophyll\ aand 40\% of ash-free dry mass by the end of the summer, while in 2012\–13 rocks regrew 18\% and 27\%, respectively. Mat stoichiometry differed between summers, and reflected differences in biomass and discharge.\ Oscillatoria\ spp. were greatest on scoured rocks and\ Phormidium\ spp. on undisturbed rocks. Small diatoms\ Humidophila\ andFistulifera\ spp. increased throughout the summer in all mats, with the latter more abundant in scoured communities. Collectively, these data suggest that mats are variable intra-annually, responsive to hydrology and require multiple summers to regrow initial biomass once lost. These results will aid the interpretation of long-term data, as well as inform Antarctic Specially Managed Area protocols.

}, keywords = {LTER-MCM}, issn = {0954-1020}, doi = {10.1017/S0954102015000024}, url = {http://www.journals.cambridge.org/abstract_S0954102015000024}, author = {Tyler J. Kohler and Ethan Chatfield and Michael N. Gooseff and John E. Barrett and Diane M. McKnight} } @article {1067, title = {Diel flow pulses drive particulate organic matter transport from microbial mats in a glacial meltwater stream in the McMurdo Dry Valleys}, journal = {Water Resources Research}, volume = {50}, year = {2014}, month = {01/2014}, pages = {86-97}, chapter = {86}, abstract = { Many glacial meltwater streams in the McMurdo Dry Valleys (MDV) of Antarctica contain abundant microbial mats, representing hot spots of primary production in a barren landscape. These mats persist through the winter in a freeze-dried state and grow in the summer, experiencing a dynamic hydrologic regime as streamflow varies on a diel cycle and with weather conditions. During diel peaks in flow these streams transport particulate organic matter (POM) to the downstream closed-basin lakes. We investigated the spatial and temporal dynamics of POM transport derived from the scouring of microbial mats in Von Guerard Stream of the MDV. The results show clockwise hysteresis effects in POM concentration over diel flood pulses and suggests that POM transport in the MDVs is supply limited. Further studies are required to confirm this and to identify the potential contributing sources of POM. The hysteresis effect was modeled using an approach derived from models of sediment transport in streams. Spatial variations in POM transport indicate that patch-scale variations in bed shear stress and benthic biomass also influence transport which is integrated downstream over several 100{\textquoteright}s of meters. Large variations in the POM transport dynamics between different diel flood pulses were found to be related to the time since a resetting flood event and the regrowth of potentially mobile benthic biomass, providing further evidence of the importance of supply limitation and flow variability in controlling the organic matter flux of stream ecosystems.}, keywords = {LTER-MCM}, doi = {10.1002/2013WR014061}, author = {Cullis, James D.S. and Lee F. Stanish and Diane M. McKnight} } @mastersthesis {4094, title = {Ecology and biogeography of freshwater diatoms in ponds of McMurdo Dry Valleys and parts of the Ross Island}, volume = {M.S.}, year = {2014}, school = {University of Colorado}, type = {masters}, address = {Boulder, CO}, abstract = {

The McMurdo Dry Valleys (MDVs) and the exposed coastal areas of the nearby Ross Island in Antarctica represent some of the coldest, driest places in the world. However, during the austral summer warmer temperatures and constant sunlight allow microbial life to flourish nearly anywhere there is water. Diatoms are single-celled algae encapsulated in a silica shell and diatom communities constitute an important component of the microbial mats that grow in the streams, lakes and ponds in these regions. As part of the Long Term Ecological Research station in the McMurdo Dry Valleys diatom communities have been studied extensively in the streams over the last 20 years. Although the diatoms present in pond microbial mats at Cape Royds have been previously studied, modern-day knowledge of the characteristics of diatom communities in ponds and small lakes throughout the region is limited. This work sought to find the relationships between water chemistry and diatom community structure in ponds. Because water flow is not a factor in ponds and small lakes, influences of salinity, nutrients, pH and other factors can be more easily distinguished. This study looked at 24 separate bodies of water in the Taylor Valley, Labyrinth region in Wright Valley, Cape Royds and McMurdo Station area on Ross Island. The results suggest that geography, dispersal and historical environmental conditions play a significant role in structuring diatom communities, in addition to water chemistry. The results also expand the knowledge of habitat preferences for some of the species present in this region.

}, keywords = {LTER-MCM, biological sciences, freshwater diatoms, health and environmental sciences, McMurdo Dry Valleys, ponds}, url = {https://search.proquest.com/docview/1655818365?accountid=14503}, author = {Sakaeva, A.}, editor = {Diane M. McKnight} } @article {1093, title = {The carbon stable isotope biogeochemistry of streams, Taylor Valley, Antarctica}, journal = {Applied Geochemistry}, volume = {32}, year = {2013}, month = {05/2013}, pages = {26 - 36}, keywords = {LTER-MCM}, doi = {10.1016/j.apgeochem.2012.08.019}, author = {W. Berry Lyons and Leslie, D.L. and Harmon, R.S. and Klaus Neumann and Kathleen A. Welch and Bisson, K. M. and Diane M. McKnight} } @article {1077, title = {Characterization of fulvic acid fractions of dissolved organic matter during ice-out in a hyper-eutrophic, coastal pond in Antarctica}, journal = {Environmental Research Letters}, volume = {8}, year = {2013}, month = {12/2013}, pages = {045015}, abstract = {Dissolved humic material (HDOM) is ubiquitous to all natural waters and its source material influences its chemical structure, reactivity, and bioavailability. While terrestrially derived HDOM reference materials distributed by the International Humic Substances Society (IHSS) have been readily available to engineering and scientific communities, a microbially derived reference HDOM was not, despite the well-characterized differences in the chemistry and reactivity of HDOM derived from terrestrial versus microbial sources. To address this gap, we collected a microbial reference fulvic acid from Pony Lake (PLFA) for distribution through the IHSS. Pony Lake is a saline coastal pond on Ross Island, Antarctica, where the landscape is devoid of terrestrial plants. Sample collection occurred over a 17-day period in the summer season at Pony Lake. During this time, the dissolved organic carbon (DOC) concentrations increased nearly two-fold, and the fulvic acid fraction (collected using the XAD-8 method) accounted for 14.6\% of the DOC. During the re-concentration and desalting procedures we isolated two other chemically distinct fulvic acid fractions: (1) PLFA-2, which was high in carbohydrates and (2) PLFA-CER, which was high in nitrogen. The chemical characteristics (elemental analysis, optical characterization with UV{\textendash}vis and fluorescence spectroscopy, and 13C NMR spectroscopy) of the three fulvic acid fractions helped to explain their behavior during isolation.}, keywords = {LTER-MCM}, doi = {10.1088/1748-9326/8/4/045015}, author = {Kaelin M. Cawley and Diane M. McKnight and Penney L. Miller and Rose M. Cory and Fimmen, Ryan L and Guerard, Jennifer and Markus Dieser and Chris Jaros and Yu-Ping Chin and Christine M. Foreman} } @article {1078, title = {Characterization of IHSS Pony Lake fulvic acid dissolved organic matter by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry and fluorescence spectroscopy}, journal = {Organic Geochemistry}, volume = {65}, year = {2013}, month = {12/2013}, pages = {19 - 28}, keywords = {LTER-MCM}, doi = {10.1016/j.orggeochem.2013.09.013}, url = {http://www.sciencedirect.com/science/article/pii/S0146638013002167}, author = {D{\textquoteright}Andrilli, Juliana and Christine M. Foreman and Marshall, Alan G. and Diane M. McKnight} } @article {1079, title = {Environmental factors influencing diatom communities in Antarctic cryoconite holes}, journal = {Environmental Research Letters}, volume = {8}, year = {2013}, month = {12/2013}, pages = {045006}, keywords = {LTER-MCM}, doi = {10.1088/1748-9326/8/4/045006}, url = {http://iopscience.iop.org/1748-9326/8/4/045006/pdf/1748-9326_8_4_045006.pdf}, author = {Lee F. Stanish and Bagshaw, Elizabeth and Diane M. McKnight and Andrew G Fountain and Martyn Tranter} } @article {1087, title = {The influence of stream thermal regimes and preferential flow paths on hyporheic exchange in a glacial meltwater stream}, journal = {Water Resources Research}, volume = {49}, year = {2013}, month = {09/2013}, pages = {5552 - 5569}, keywords = {LTER-MCM}, doi = {10.1002/wrcr.20410}, url = {http://onlinelibrary.wiley.com/doi/10.1002/wrcr.20410/pdf}, author = {Cozzetto, K and Kenneth E. Bencala and Michael N. Gooseff and Diane M. McKnight} } @article {1088, title = {Microbial growth under humic-free conditions in a supraglacial stream system on the Cotton Glacier, Antarctica}, journal = {Environmental Research Letters}, volume = {8}, year = {2013}, month = {09/2013}, pages = {035022}, abstract = {During the austral summers of 2004 and 2009, we sampled a supraglacial stream on the Cotton Glacier, Antarctica. The stream dissolved organic matter (DOM) was low (44{\textendash}48 μM C) and lacked detectable humic fluorescence signatures. Analysis of the excitation emissions matrices (EEMs) indicated that amino-acid fluorophores dominated, consistent with DOM of microbial origin, with little humic-like fluorescence. In most aquatic ecosystems, humic DOM attenuates harmful UV radiation and its absence may represent an additional stressor influencing the microbial community. Nonetheless, the stream contained an active microbial assemblage with bacterial cell abundances from 2.94 {\texttimes} 104 to 4.97 {\texttimes} 105 cells ml-1, and bacterial production ranging from 58.8 to 293.2 ng C l-1 d-1. Chlorophyll-a concentrations ranged from 0.3 to 0.53 μg l-1 indicating that algal phototrophs were the probable source of the DOM. Microbial isolates produced a rainbow of pigment colors, suggesting adaptation to stress, and were similar to those from other cryogenic systems (Proteobacteria and Bacteroidetes lineages). Supraglacial streams provide an example of contemporary microbial processes on the glacier surface and a natural laboratory for studying microbial adaptation to the absence of humics.}, keywords = {LTER-MCM}, doi = {10.1088/1748-9326/8/3/035022}, url = {http://iopscience.iop.org/1748-9326/8/3/035022}, author = {Christine M. Foreman and Rose M. Cory and Morris, Cindy E and Michael D. SanClements and Smith, Heidi J and John T. Lisle and Penney L. Miller and Yu-Ping Chin and Diane M. McKnight} } @article {1081, title = {Physicochemical and biological dynamics in a coastal Antarctic lake as it transitions from frozen to open water}, journal = {Antarctic Science}, volume = {25}, year = {2013}, month = {12/2013}, pages = {663{\textendash}675}, keywords = {LTER-MCM}, author = {Markus Dieser and Christine M. Foreman and Chris Jaros and John T. Lisle and Mark C. Greenwood and Johanna Laybourn-Parry and Penney L. Miller and Yu-Ping Chin and Diane M. McKnight} } @article {1115, title = {Bacteria and diatom co-occurrence patterns in microbial mats from polar desert streams}, journal = {Environmental Microbiology}, year = {2012}, month = {10/2012}, keywords = {LTER-MCM}, doi = {10.1111/j.1462-2920.2012.02872.x}, url = {http://onlinelibrary.wiley.com/doi/10.1111/j.1462-2920.2012.02872.x/abstract}, author = {Lee F. Stanish and Sean P. O{\textquoteright}Neill and Antonio Gonz{\'a}lez and Teresa M. Legg and Joseph Knelman and Diane M. McKnight and Sarah A. Spaulding and Diana R. Nemergut} } @article {1122, title = {The ecology of pulse events: insights from an extreme climatic event in a polar desert ecosystem}, journal = {Ecosphere}, volume = {3}, year = {2012}, month = {02/2012}, pages = {art17}, keywords = {LTER-MCM}, doi = {10.1890/ES11-00325.1}, url = {http://www.esajournals.org/doi/abs/10.1890/ES11-00325.1}, author = {Uffe N. Nielsen and Diana H. Wall and Byron Adams and Ross A. Virginia and Ball, Becky and Michael N. Gooseff and Diane M. McKnight} } @article {1116, title = {Extreme streams: flow intermittency as a control on diatom communities in meltwater streams in the McMurdo Dry Valleys, Antarctica}, journal = {Canadian Journal of Fisheries and Aquatic Sciences}, volume = {69}, year = {2012}, month = {08/2012}, pages = {1405 - 1419}, keywords = {LTER-MCM}, doi = {10.1139/f2012-022}, url = {http://www.nrcresearchpress.com/doi/abs/10.1139/f2012-022$\#$.UH2NlWcnq9g}, author = {Lee F. Stanish and Tyler J. Kohler and Rhea M.M. Esposito and Breana L. Simmons and Uffe N. Nielsen and Diana H. Wall and Diana R. Nemergut and Diane M. McKnight} } @article {3528, title = {Microbial life at -13 ~C in the brine of an ice-sealed Antarctic lake}, journal = {Proceedings of the National Academy of Sciences}, volume = {109}, year = {2012}, month = {12/2012}, pages = {20626 - 20631}, keywords = {LTER-MCM}, issn = {0027-8424}, doi = {10.1073/pnas.1208607109}, url = {http://www.pnas.org/cgi/doi/10.1073/pnas.1208607109}, author = {A. E. Murray and Kenig, Fabien and Christian H. Fritsen and Christopher P. McKay and Kaelin M. Cawley and R. L. Edwards and Kuhn, Emanuele and Diane M. McKnight and Nathaniel E Ostrom and Vivian Peng and Adrian Ponce and John C. Priscu and Samarkin, Vladimir A. and Ashley T Townsend and Protima Wagh and Seth A Young and Pung To Yung and Peter T. Doran} } @article {1130, title = {15N and 13C{14N} NMR investigation of the major nitrogen-containing segment in an aquatic fulvic acid: Evidence for a hydantoin derivative}, journal = {Magnetic Resonance in Chemistry}, volume = {49}, year = {2011}, month = {12/2011}, pages = {775 - 780}, keywords = {LTER-MCM}, doi = {10.1002/mrc.2816}, author = {Xiaowen Fang and Jingdong Mao and Rose M. Cory and Diane M. McKnight and Klaus Schmidt-Rohr} } @phdthesis {4095, title = {Ecological controls on stream diatom communities in the McMurdo Dry Valleys, Antarctica}, volume = {Ph.D.}, year = {2011}, school = {University of Colorado}, type = {doctoral}, address = {Boulder, CO}, abstract = {

Diatoms are vital primary producers in aquatic ecosystems and useful indicators of environmental change. In climatically sensitive polar areas, diatoms have been used as beacons of climate change, allowing us to monitor physical, chemical, and biological changes. This research aims to improve our understanding of diatom ecology in the pristine and dynamic McMurdo Dry Valleys of Antarctica, where diatoms reside in stream microbial mats. These results aid in understanding how changes in hydrologic regime will affect stream microbial communities, biodiversity, and ecosystem function in a changing environment.

Relationships between hydrologic regime and diatom community composition were investigated using long-term data. Diatom communities were structured by stream physical features, and streams with more similar hydrologic characteristics had more similar communities. Variation in diatom community composition was best explained by hydrologic regime. Small diatoms increased in relative abundances with increasing streamflow, suggesting a role of diatom size in structuring communities. Overall, diatom communities were resistant to flood and drought-like conditions, suggesting an adaptation to frequent disturbances.

The importance of hydrologic regime on drift activity was investigated during three 24- hour experiments. Diel variations in drift could be attributed to diurnal flow peaks. Biomass and diatom cell densities followed a clockwise pattern with stream discharge and support the dominant role of hydraulic processes. The quality of source material differed between seasons and throughout the day. Drifting diatom communities were dominated by\ Fistulifera pelliculosa, which is rarely found in stream mats and suggests a different source. Modeling results suggest that the less firmly anchored marginal mats contribute more to the drift than channel mats in low- flow seasons, while the channel mats become more important during high-flow seasons.

The relationships between diatom and bacterial assemblages in microbial mats were assessed based on phylogenetic and functional relatedness in five Dry Valley streams. Significant relationships between diatom and bacterial communities were found, and co-occurrence analysis identified numerous correlations between individual diatom and bacterial taxa. A consistency in metabolic lifestyles of correlated taxa suggests that the relationships are ecologically relevant. Diatom and bacterial diversity showed opposite patterns, which indicate differences in environmental drivers of diversity for bacteria and eukaryotes.

}, keywords = {LTER-MCM, Antarctica, biological sciences, community ecology, diatoms, earth sciences, McMurdo Dry Valleys, streams}, url = {https://search.proquest.com/docview/915694114?accountid=14503}, author = {Lee F. Stanish}, editor = {Diane M. McKnight} } @article {1131, title = {Hydrologic processes influence diatom community composition in Dry Valley streams}, journal = {Journal of the North American Benthological Society}, volume = {30}, year = {2011}, month = {12/2011}, pages = {1057-1073}, keywords = {LTER-MCM}, doi = {10.1899/11-008.1}, url = {http://www.jnabs.org/doi/abs/10.1899/11-008.1}, author = {Lee F. Stanish and Diana R. Nemergut and Diane M. McKnight} } @article {1135, title = {Hydrological Connectivity of the Landscape of the McMurdo Dry Valleys, Antarctica}, journal = {Geography Compass}, volume = {5}, year = {2011}, month = {09/2011}, pages = {666 - 681}, keywords = {LTER-MCM}, doi = {10.1111/j.1749-8198.2011.00445.x}, url = {http://onlinelibrary.wiley.com/doi/10.1111/j.1749-8198.2011.00445.x}, author = {Michael N. Gooseff and Diane M. McKnight and Peter T. Doran and Andrew G Fountain and W. Berry Lyons} } @phdthesis {4085, title = {Removal of benthic algae in swift-flowing streams: The significance of spatial and temporal variation in shear stress and bed disturbance}, volume = {Ph.D.}, year = {2011}, pages = {263}, school = {University of Colorado}, type = {doctoral}, address = {Boulder, CO}, abstract = {

In this thesis I investigate the role of spatial and temporal dynamics of flow, bed shear stress, and bed disturbance on the removal of benthic algal and the consequences for our understanding of the dynamics of stream ecosystems and the transport of organic matter in fluvial systems. I use data obtained from two specific case studies where benthic algal mats are key components in the overall system dynamics. The first case study investigates spatial and temporal variations in particular organic matter transport derived from the removal of benthic algae in a stream in the McMurdo Dry Valleys of Antarctica. The second case study uses a combination of field observations and analysis, one and two dimensional hydraulic modeling, and laboratory flume studies to investigate the controls on the removal of the stalk forming diatom\ Didymosphenia geminata. The results show that benthic algae growing in swift-flowing streams are well adapted to this environment. Hence the removal of organic material due to elevated shear stress alone is limited and effective control of nuisance blooms of benthic algae such as\ D. geminata\ requires flood events sufficiently high enough to results in wide spread disturbance of the stream substrate. These flow requirements are similar to the requirements for channel maintenance flows and could therefore be considered for inclusion in the operating rules for dams in order to maintain the diversity of stream ecosystems and functioning water supply infrastructure.

}, keywords = {LTER-MCM}, url = {https://search.proquest.com/docview/916604693?accountid=14503}, author = {Cullis, James D.S.}, editor = {Diane M. McKnight} } @article {1129, title = {Simulating unsteady flow, anabranching, and hyporheic dynamics in a glacial meltwater stream using a coupled surface water routing and groundwater flow model}, journal = {Water Resources Research}, volume = {47}, year = {2011}, month = {2011}, keywords = {LTER-MCM}, doi = {10.1029/2010WR009508}, author = {Koch, J. and Diane M. McKnight and Neupauer, R. M.} } @book {1146, title = {Spectral Methods to Advance Understanding of Dissolved Organic Carbon Dynamics in Forested Catchments}, series = {Ecological StudiesForest Hydrology and Biogeochemistry}, volume = {216}, year = {2011}, pages = {117 - 135}, publisher = {Springer Netherlands}, organization = {Springer Netherlands}, address = {Dordrecht}, keywords = {LTER-MCM}, isbn = {978-94-007-1363-5}, doi = {10.1007/978-94-007-1363-5_6}, url = {http://www.springerlink.com/content/lv9365ml54192m29/}, author = {Rose M. Cory and Elizabeth W. Boyer and Diane M. McKnight}, editor = {Levia, Delphis F. and Carlyle-Moses, Darryl and Tanaka, Tadashi} } @article {1138, title = {When a habitat freezes solid: microorganisms over-winter within the ice column of a coastal Antarctic lake}, journal = {FEMS Microbiology Ecology}, volume = {76}, year = {2011}, month = {06/2011}, pages = {401 - 412}, keywords = {LTER-MCM}, doi = {10.1111/j.1574-6941.2011.01061.x}, url = {http://onlinelibrary.wiley.com/doi/10.1111/j.1574-6941.2011.01061.x/full}, author = {Christine M. Foreman and Markus Dieser and Mark Greenwood and Rose M. Cory and Johanna Laybourn-Parry and John T. Lisle and Chris Jaros and Penney L. Miller and Yu-Ping Chin and Diane M. McKnight} } @inbook {1168, title = {Antarctic McMurdo Dry Valley stream ecosystems as analog to fluvial systems on Mars}, booktitle = {Life in Antarctic Deserts and other Cold Dry Environments}, year = {2010}, pages = {139 - 159}, publisher = {Cambridge University Press}, organization = {Cambridge University Press}, address = {Cambridge}, keywords = {LTER-MCM}, isbn = {9780521889193}, doi = {10.1017/CBO9780511712258.005}, author = {Michael N. Gooseff and Diane M. McKnight and Carr, M. H. and Baeseman, J.}, editor = {Peter T. Doran and W. Berry Lyons and Diane M. McKnight} } @inbook {1170, title = {Diatoms as indicators of environmental change in Antarctic and subantarctic freshwaters}, booktitle = {The Diatoms Applications for the Environmental and Earth Sciences}, year = {2010}, publisher = {Cambridge University Press}, organization = {Cambridge University Press}, edition = {2}, keywords = {LTER-MCM}, isbn = {9780521509961}, url = {http://www.cambridge.org/us/academic/subjects/life-sciences/plant-science/diatoms-applications-environmental-and-earth-sciences-2nd-edition}, author = {Sarah A. Spaulding and Bart Van de Vijver and Hodgson, D and Diane M. McKnight and Elie Verleyen and Lee F. Stanish} } @article {1161, title = {Effect of instrument-specific response on the analysis of fulvic acid fluorescence spectra}, journal = {Limnology and Oceanography: Methods}, volume = {8}, year = {2010}, month = {07/2010}, pages = {67-78}, keywords = {LTER-MCM}, url = {http://www.aslo.org/lomethods/free/2010/0067.html}, author = {Rose M. Cory and Mathew P. Miller and Diane M. McKnight and Guerard, Jennifer and Penney L. Miller} } @article {4816, title = {Effect of unsteady flow on nitrate loss in an oligotrophic, glacial meltwater stream}, journal = {Journal of Geophysical Research}, volume = {115}, year = {2010}, month = {03/2010}, pages = {G01001}, abstract = {

The McMurdo Dry Valleys of Antarctica are among the coldest, driest ecosystems on Earth. During the austral summer, glacial meltwater supports cyanobacterial mat communities in some streams, but they are not ubiquitous. We conducted a nitrate (NO3-) enrichment tracer injection in Huey Creek to quantify NO3- loss in a Dry Valley stream where algal mats would not obscure hyporheic microbial processes. Unsteady streamflow led to diel variability in the tracer concentration and in surface/subsurface water and solute exchange. Subsequently, concentrations of NO3-, nitrite (NO2-), ammonium (NH4+), and dissolved organic carbon (DOC) varied significantly during the injection, with a net loss of NO3-, NO2-, and DOC, and production of nitrous oxide. These mass changes within a reach were often coincident with high streamflows. Reactivity also coincided with the highest DOC concentrations, suggesting that DOC is the primary limitation to heterotrophic microbial activity in the stream. Together, streamflow and DOC availability create the hot spots and hot moments that dominate NO3- reactivity and removal in this polar desert ecosystem. The combination of spatially and temporally variable hyporheic dynamics and solute availability underscore the limitations of common nutrient uptake metrics and transient storage models when unsteady flow conditions exist.

}, keywords = {LTER-MCM, Antarctica, hot spots/hot moments, hyporheic exchange, nitrogen cycling, unsteady flow}, doi = {10.1029/2009JG001030}, url = {http://doi.wiley.com/10.1029/2009JG001030}, author = {Koch, J. and Diane M. McKnight and Baeseman, J.} } @phdthesis {4190, title = {Hydrologic and biogeochemical implications of flooding in two catchments underlain by continuous permafrost}, volume = {Ph.D.}, year = {2010}, month = {2010}, pages = {206}, school = {University of Colorado}, type = {doctoral}, address = {Boulder, CO}, abstract = {

Flooding is a critical driver of ecosystem productivity. By rapidly increasing stream stage and velocity, floods mix water and solutes from the stream, hyporheic zone, and floodplains/riparian areas. Such mixing may spur biogeochemical activity. In catchments underlain by permafrost, flooding is more common due to both the potential for rapid ice melting and minimal storage potential in frozen soils. High latitude environments are often underlain by permafrost and are also areas of biogeochemical interest, due to large stores of carbon (C) and nitrogen (N), and the potential for rapid cycling. The increased complexity in groundwater/surface water hydrology during floods requires rigorous hydrologic analysis before biogeochemical trends can be correctly interpreted. This research aims to accurately quantify the hydrology and biogeochemical cycling of C and N in two high-latitude catchments utilizing stream tracer additions, synoptic sampling, and surface water (sw), groundwater (gw), and coupled sw/gw flow models.

Two catchments, in Alaska and Antarctica represent very different ecosystems, both characterized by continuous permafrost and shallow aquifers. In Antarctica, coupled surface water/groundwater flow modeling and tracer additions identify sources of DOC (dissolved organic carbon) and locations of denitrification. Mass balance calculations identify heightened water/sediment interactions at high flows, and increased C and N uptake when solutes return to the stream during low flows. In Alaska, discharge correlates to DOC and nitrate concentrations, indicating leaching and flushing of organic material from the hillslope during high discharge, with a greater potential for microbial processing of this organic material during low flows. Multiple tracer additions demonstrate a seasonal trend, with the greatest C and N uptake early in the summer, potentially related to shallower flowpaths.

Differences between discharge, flooding, and C and N cycling in these two catchments indicate the importance of stream size and morphology. Using tracer dilution and major ion and uranium isotope chemistry, we identify preferential flow near and beneath the stream, indicating erosion of the stream bed via soil piping and thermokarsting. We propose that channel evolution will lead to decreased stream/catchment interactions and subsequently decreased C and N uptake potential in these high-latitude catchments.

}, keywords = {LTER-MCM, carbon, catchments, earth sciences, flooding, nitrogen, permafrost, surface-groundwater interactions}, url = {https://search.proquest.com/docview/839008865}, author = {Koch, J. and Diane M. McKnight} } @book {1173, title = {Life in Antarctic Deserts and Other Cold Environments}, series = {Astrobiological Analogs}, volume = {5}, year = {2010}, pages = {307}, publisher = {Cambridge University Press.}, organization = {Cambridge University Press.}, address = {Cambridge}, keywords = {LTER-MCM, Planetary Science}, isbn = {9780511712258}, doi = {10.1017/CBO9780511712258}, url = {http://ebooks.cambridge.org/ebook.jsf?bid=CBO9780511712258}, author = {Peter T. Doran and W. Berry Lyons and Diane M. McKnight}, editor = {Diane M. McKnight and Michael N. Gooseff and Cristina D. Takacs-Vesbach and Jill A. Mikucki and Martyn Tranter and Sun, Henry J} } @phdthesis {1177, title = {Microbial interactions with dissolved organic matter in saline natural waters}, year = {2010}, school = {University of Colorado}, type = {doctoral}, keywords = {LTER-MCM}, doi = {LTER}, author = {Cawley, K} } @article {1174, title = {Physiochemical properties influencing biomass abundance and primary production in Lake Hoare, Antarctica}, journal = {Ecological Modelling}, year = {2010}, keywords = {LTER-MCM}, doi = {LTER}, author = {Herbei, Radu and W. Berry Lyons and Johanna Laybourn-Parry and Christopher B. Gardner and John C. Priscu and Diane M. McKnight} } @article {1154, title = {Spatial variations in the geochemistry of glacial meltwater streams in the Taylor Valley, Antarctica}, journal = {Antarctic Science}, volume = {22}, year = {2010}, month = {12/2010}, pages = {662 - 672}, keywords = {LTER-MCM}, doi = {10.1017/S0954102010000702}, url = {http://www.montana.edu/lkbonney/DOCS/Publications/WelchEtAl2010Geochemistry.pdf}, author = {Kathleen A. Welch and W. Berry Lyons and Whisner, Carla and Christopher B. Gardner and Michael N. Gooseff and Diane M. McKnight and John C. Priscu} } @phdthesis {4191, title = {Controls on stream and hyporheic temperatures, Taylor Valley, Antarctica and large-scale climate influences on interannual flow variation in the Onyx River, Antarctica}, volume = {Ph.D.}, year = {2009}, month = {2009}, pages = {317}, school = {University of Colorado}, type = {doctoral}, address = {Boulder, CO}, abstract = {

The McMurdo Dry Valleys comprise the largest ice-free polar desert on the continent of Antarctica. My Ph.D. research investigated summertime glacial meltwater streams flowing through this region. This work is presented in Chapters 2 through 6 of my thesis. Chapters 2-5 present the work I have done related to hyporheic processes while Chapter 6 focuses on the hydroclimatological investigations I have carried out.

More specifically, Chapter 2 addresses the question: what are the dominant processes controlling dry valley stream temperatures? In particular, this investigation quantified the role of hyporheic exchange. The study found that in the Dry Valleys, exchange acted to decrease stream temperatures, accounting for 6\–21\% of cooling.

Chapter 3 discusses a follow up tracer study to investigate whether the comparatively large daily changes in dry valley stream temperatures (6-9\°C) affect hyporheic processes, for instance through viscosity effects. Results showed that the hyporheic zone volume and exchange coefficient were lower during the warmer, afternoon stream/streambed temperature regime than during the cooler, morning one. A temperature-induced feedback mechanism that increases subsurface flow path preferentiality is proposed as a possible explanation for the reduction in hyporheic volume under warmer conditions. The tracer results also suggested a \“Swiss Cheese\” type conceptual model of the hyporheic zone in which flow takes place along paths weaving their way through isolated areas.

Chapter 4 presents work done to elucidate individual hyporheic flow path lengths and residence times. A streambed injection revealed some long (over 100 m) paths that were also fast, having subsurface travel times on par with the surface water. Hyporheic pipeflow is proposed as an explanation.

In Chapter 5 research is presented showing that nitrate and phosphate concentrations at specific locations in the hyporheic zone increase with the decreasing connectivity of that location to the stream.

Finally, Chapter 6 describes the large-scale climate conditions that prevailed during December and January during the highest and lowest flow summers of the Onyx River record, the longest flow record for Antarctica. Climate variables and regions in the Southern Hemisphere that had a statistically significant linear correlation to Onyx River flows were also identified. The highest flow summer on record, 2001-2, was found to have some unusual climate features when compared to the other high flow summers. It stands out as having an anomalous wind pattern that would have increased katabatic winds in the valleys, raising air temperatures and possibly depositing sediment on the glaciers, decreasing their albedo. It is also characterized by anomalously high incoming shortwave radiation. We postulate that those high levels may have been due in part to the unusually low concentrations of radiation absorbing stratospheric ozone prevalent over the valleys that particular summer.

}, keywords = {LTER-MCM, Antarctica, earth sciences, hydroclimatology, hyporheic flow paths, hyporheic zone, stream temperature}, url = {https://search.proquest.com/docview/304866366}, author = {Cozzetto, K and Diane M. McKnight} } @article {1181, title = {Lakes and reservoirs as regulators of carbon cycling and climate}, journal = {Limnology and Oceanography}, volume = {54 part 2}, year = {2009}, month = {11/2009}, pages = {2298{\textendash}2314}, keywords = {LTER-MCM}, doi = {10.4319/lo.2009.54.6_part_2.2298}, url = {http://aslo.org/lo/toc/vol_54/issue_6_part_2/2298.pdf}, author = {Lars J. Tranvik and John A. Downing and James B. Cotner and Steven A. Loiselle and Robert G. Striegl and Thomas J. Ballatore and Peter Dillon and Kerri Finlay and Kenneth Fortino and Lesley B. Knoll and Pirkko L. Kortelainen and Tiit Kutser and Soren Larsen and Isabelle Laurion and Dina M. Leech and S. Leigh McCallister and Diane M. McKnight and John M. Melack and Erin Overholt and Jason A. Porter and Yves Prairie and William H. Renwick and Fabio Roland and Bradford S. Sherman and David W. Schindler and Sebastian Sobek and Alain Tremblay and Michael J. Vanni and Antonie M. Verschoor and Eddie von Wachenfeldt and Gesa A. Weyhenmeyer} } @inbook {1214, title = {High-latitude rivers and streams.}, booktitle = {Polar Lakes and Rivers: Limnology of Arctic and Antarctic Aquatic Ecosystems}, year = {2008}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {Oxford}, keywords = {LTER-MCM}, doi = {LTER}, author = {Diane M. McKnight and Michael N. Gooseff and Warwick F. Vincent and Peterson, B}, editor = {Warwick F. Vincent and Johanna Laybourn-Parry} } @article {1204, title = {Hydrologic response to extreme warm and cold summers in the McMurdo Dry Valleys, East Antarctica}, journal = {Antarctic Science}, volume = {20}, year = {2008}, month = {05/16/2008}, pages = {499-509}, type = {Journal}, keywords = {LTER-MCM, Climate Response, streams}, doi = {10.1017/S0954102008001272}, author = {Peter T. Doran and Christopher P. McKay and Andrew G Fountain and Thomas H. Nylen and Diane M. McKnight and Chris Jaros and John E. Barrett} } @article {1216, title = {Inland diatoms from the McMurdo Dry Valleys and James Ross Island, Antarctica}, journal = {Botany-Botanique}, volume = {12}, year = {2008}, pages = {1378-1392}, keywords = {LTER-MCM}, doi = {LTER}, author = {Rhea M.M. Esposito and Sarah A. Spaulding and Diane M. McKnight and De Vijver, B and Kopalova, K and Lubinski, D and Brenda L. Hall and Whittaker, T} } @article {1236, title = {Biogeochemical stoichiometry of Antarctic Dry Valley ecosystems}, journal = {Journal of Geophysical Research}, volume = {112}, year = {2007}, month = {02/2007}, pages = {G01010+12}, abstract = {

Among aquatic and terrestrial landscapes of the McMurdo Dry Valleys, Antarctica, ecosystem stoichiometry ranges from values near the Redfield ratios for C:N:P to nutrient concentrations in proportions far above or below ratios necessary to support balanced microbial growth. This polar desert provides an opportunity to evaluate stoichiometric approaches to understand nutrient cycling in an ecosystem where biological diversity and activity are low, and controls over the movement and mass balances of nutrients operate over 10\–106\ years. The simple organisms (microbial and metazoan) comprising dry valley foodwebs adhere to strict biochemical requirements in the composition of their biomass, and when activated by availability of liquid water, they influence the chemical composition of their environment according to these ratios. Nitrogen and phosphorus varied significantly in terrestrial and aquatic ecosystems occurring on landscape surfaces across a wide range of exposure ages, indicating strong influences of landscape development and geochemistry on nutrient availability. Biota control the elemental ratio of stream waters, while geochemical stoichiometry (e.g., weathering, atmospheric deposition) evidently limits the distribution of soil invertebrates. We present a conceptual model describing transformations across dry valley landscapes facilitated by exchanges of liquid water and biotic processing of dissolved nutrients. We conclude that contemporary ecosystem stoichiometry of Antarctic Dry Valley soils, glaciers, streams, and lakes results from a combination of extant biological processes superimposed on a legacy of landscape processes and previous climates.

}, keywords = {LTER-MCM, Biggie}, doi = {10.1029/2005JG000141}, author = {John E. Barrett and Ross A. Virginia and W. Berry Lyons and Diane M. McKnight and John C. Priscu and Andrew G Fountain and Diana H. Wall and Daryl L. Moorhead and Peter T. Doran} } @article {1235, title = {Reactivation of a cryptobiotic stream ecosystem in the McMurdo Dry Valleys, Antarctica: A long-term geomorphological experiment}, journal = {Geomorphology}, volume = {89}, year = {2007}, month = {09/2007}, pages = {186-204}, keywords = {LTER-MCM}, doi = {10.1016/j.geomorph.2006.07.025}, author = {Diane M. McKnight and Cathy M. Tate and Edmund D. Andrews and Dev K. Niyogi and Cozzetto, K and Kathleen A. Welch and W. Berry Lyons and D. G. Capone} } @proceedings {1251, title = {Trends in discharge and flow season timing of the Onyx River, Wright Valley, Antarctica since 1969}, journal = {Antarctica; A keystone in a changing world--online proceedings for the tenth international symposium}, year = {2007}, publisher = {U.S. Geological Survey Open-File Report 2007-1047}, keywords = {LTER-MCM}, doi = {LTER}, author = {Michael N. Gooseff and Diane M. McKnight and Peter T. Doran and W. Berry Lyons}, editor = {Alan Cooper and Carol Raymond and ISAES Editorial Team} } @article {1256, title = {Antarctic Climate Cooling and Response of Diatoms in Glacial Meltwater Streams}, journal = {Geophysical Research Letters}, volume = {33}, year = {2006}, month = {04/2006}, pages = {L07406}, type = {Journal}, abstract = {

To understand biotic responses to an Antarctic cooling trend, we analyzed diatom samples from glacial meltwater streams in the McMurdo Dry Valleys, the largest ice-free area in Antarctica. Diatoms are abundant in these streams, and 24 of 40 species have only been found in the Antarctic. The percentage of these Antarctic diatom species increased with decreasing annual stream flow and increasing harshness of the stream habitat. The species diversity of assemblages reached a maximum when the Antarctic species accounted for 40\–60\% of relative diatom abundance. Decreased solar radiation and air-temperatures reduce annual stream flow, raising the dominance of these Antarctic species to levels above 60\%. Thus, cooling favors the Antarctic species, and lowers diatom species diversity in this region.

}, keywords = {LTER-MCM, Biggie}, doi = {10.1029/2006GL025903}, author = {Rhea M.M. Esposito and Horn, S and Diane M. McKnight and Cox, M and Grant, M and Sarah A. Spaulding and Peter T. Doran and Cozzetto, K} } @article {1267, title = {Experimental investigations into processes controlling stream and hyporheic temperatures, Fryxell Basin, Antarctica}, journal = {Advances in Water Resources}, volume = {29}, year = {2006}, pages = {130-153}, keywords = {LTER-MCM}, doi = {LTER}, author = {Cozzetto, K and Diane M. McKnight and Thomas H. Nylen and Andrew G Fountain} } @book {1271, title = {The Lost Seal}, year = {2006}, pages = {40}, publisher = {Moonlight Publishing LLC}, organization = {Moonlight Publishing LLC}, address = {Lafayette}, keywords = {LTER-MCM}, isbn = {978-0972342278}, doi = {LTER}, author = {Diane M. McKnight} } @article {1275, title = {Spatial and temporal active layer dynamics along three glacial meltwater streams in the McMurdo Dry Valleys, Antarctica}, journal = {Arctic Antarctic and Alpine Research}, volume = {38}, year = {2006}, pages = {42-53}, keywords = {LTER-MCM}, doi = {LTER}, author = {Peter A. Conovitz and Lee H. MacDonald and Diane M. McKnight} } @article {1258, title = {A stable isotopic investigation of a polar desert hydrologic system, McMurdo Dry Valleys, Antarctica}, journal = {Arctic, Antarctic, and Alpine Research}, volume = {38}, year = {2006}, month = {02/2006}, pages = {60-71}, keywords = {LTER-MCM}, doi = {10.1657/1523-0430(2006)038[0060:ASIIOA]2.0.CO;2}, author = {Michael N. Gooseff and W. Berry Lyons and Diane M. McKnight and Bruce H. Vaughn and Andrew G Fountain and Carolyn Dowling} } @article {1293, title = {Comment on {\textquoteleft}{\textquoteleft}El Ni{\~n}o suppresses Antarctic warming{\textquoteright}{\textquoteright} by N. Bertler et al.}, journal = {Geophysical Research Letters}, volume = {32}, year = {2005}, pages = {L07706}, keywords = {LTER-MCM, Tropical meteorology}, doi = {10.1029/2004GL021716}, author = {Peter T. Doran and Gary D. Clow and Christian H. Fritsen and Christopher P. McKay and Andrew N. Parsons and John C. Priscu and W. Berry Lyons and Walsh, J and Andrew G Fountain and Diane M. McKnight and Daryl L. Moorhead and Ross A. Virginia and Diana H. Wall} } @article {1288, title = {Sensitivity analysis of conservative and reactive stream transient storage models applied to field data from multiple-reach experiments}, journal = {Advances in Water Resources}, volume = {28}, year = {2005}, month = {05/2005}, pages = {479-492}, keywords = {LTER-MCM}, doi = {10.1016/j.advwatres.2004.11.012}, author = {Michael N. Gooseff and Kenneth E. Bencala and Durelle T. Scott and Robert L. Runkel and Diane M. McKnight} } @article {1325, title = {Changes in fulvic acid redox state through the oxycline of a permanently ice-covered Antarctic lake}, journal = {Aquatic Sciences}, volume = {66}, year = {2004}, pages = {1-20}, keywords = {LTER-MCM}, author = {Fulton, J and Diane M. McKnight and Christine M. Foreman and Rose M. Cory and Stedmon, C and Blunt, E} } @article {1319, title = {Denitrification and hydrologic transient storage in a glacial meltwater stream, McMurdo Dry Valleys, Antarctica}, journal = {Limnology and Oceanography}, volume = {49}, year = {2004}, month = {09/2004}, pages = {1884-1895}, keywords = {LTER-MCM}, doi = {10.4319/lo.2004.49.5.1884}, author = {Michael N. Gooseff and Diane M. McKnight and Robert L. Runkel and John H. Duff} } @article {1335, title = {Inorganic nitrogen and phosphorus dynamics of Antarctic glacial meltwater streams as controlled by hyporheic exchange and benthic autotrophic communities}, journal = {Journal of the North American Benthological Society}, volume = {23}, year = {2004}, pages = {171-188}, keywords = {LTER-MCM}, author = {Diane M. McKnight and Robert L. Runkel and John H. Duff and Cathy M. Tate and Daryl L. Moorhead} } @article {1341, title = {Reach-scale cation exchange controls on major ion chemistry of an Antarctic glacial meltwater stream}, journal = {Special issue of Aquatic Geochemistry on the McMurdo Dry Valleys}, volume = {10}, year = {2004}, pages = {221-238}, keywords = {LTER-MCM}, author = {Michael N. Gooseff and Diane M. McKnight and Robert L. Runkel} } @article {1358, title = {Biochemistry of Si in the McMurdo Dry Valley lakes, Antarctica}, journal = {The International Journal of Astrobiology}, volume = {1}, year = {2003}, pages = {737-749}, keywords = {LTER-MCM}, author = {Pugh, H and Kathleen A. Welch and W. Berry Lyons and John C. Priscu and Diane M. McKnight} } @inbook {1360, title = {Chemistry and lake dynamics of the Taylor Valley lakes, Antarctica: The importance of long-term monitoring.}, booktitle = {Antarctic Ecosystems: Models for Wider Ecological Understanding}, year = {2003}, publisher = {Caxton Press}, organization = {Caxton Press}, keywords = {LTER-MCM}, author = {Kathleen A. Welch and Klaus Neumann and W. Berry Lyons and Diane M. McKnight}, editor = {Clive Howard-Williams and W. Davidson and P. Broady} } @article {1361, title = {Determining long time-scale hyporheic zone flow paths in Antarctic streams}, journal = {Hydrological Processes}, volume = {17}, year = {2003}, pages = {1691-1710}, keywords = {LTER-MCM}, author = {Michael N. Gooseff and Diane M. McKnight and Robert L. Runkel and Bruce H. Vaughn} } @article {1369, title = {Surface glaciochemistry of Taylor Valley, southern Victoria Land, Antarctica and its relationship to stream chemistry.}, journal = {Hydrological Processes}, volume = {17}, year = {2003}, pages = {115-130}, keywords = {LTER-MCM}, author = {W. Berry Lyons and Kathleen A. Welch and Andrew G Fountain and Gayle L. Dana and Bruce H. Vaughn and Diane M. McKnight} } @article {1377, title = {Antarctic climate cooling and terrestrial ecosystem response}, journal = {Nature}, volume = {415}, year = {2002}, month = {01/2002}, pages = {517-520}, type = {Journal}, keywords = {LTER-MCM, Climate Response}, doi = {10.1038/nature710}, author = {Peter T. Doran and John C. Priscu and W. Berry Lyons and John E. Walsh and Andrew G Fountain and Diane M. McKnight and Daryl L. Moorhead and Ross A. Virginia and Diana H. Wall and Gary D. Clow and Christian H. Fritsen and Christopher P. McKay and Andrew N. Parsons} } @mastersthesis {1388, title = {Climatic controls on interannual variation in streamflow in Fryxell Basin, Taylor Valley}, volume = {M.S.}, year = {2002}, school = {University of Colorado}, type = {masters}, keywords = {LTER-MCM}, doi = {LTER}, author = {Chris Jaros} } @article {1378, title = {Direct observation of aluminosilicate weathering in the hyporheic zone of an Antarctic Dry Valley stream}, journal = {Geochimica et Cosmochimica Acta}, volume = {66}, year = {2002}, pages = {1335-1347}, keywords = {LTER-MCM}, author = {Maurice, P and Diane M. McKnight and Leff, L and Fulghun, J and Michael N. Gooseff} } @mastersthesis {1391, title = {Interannual variation in phytoplankton dynamics in Lake Fryxell}, volume = {M.S.}, year = {2002}, school = {University of Colorado}, type = {masters}, keywords = {LTER-MCM}, doi = {LTER}, author = {Van Matre, E} } @article {1382, title = {Recent Temperature Trends in the Antarctic}, journal = {Nature}, volume = {418}, year = {2002}, pages = {291-292}, keywords = {LTER-MCM}, author = {John E. Walsh and Gary D. Clow and Christian H. Fritsen and Christopher P. McKay and Andrew N. Parsons and Peter T. Doran and John C. Priscu and W. Berry Lyons and Andrew G Fountain and Diane M. McKnight and Daryl L. Moorhead and Ross A. Virginia and Diana H. Wall} } @article {1375, title = {Weathering reactions and hyporheic exchange controls on stream water chemistry in a glacial meltwater stream in the McMurdo Dry Valleys}, journal = {Water Resources Research}, volume = {38}, year = {2002}, month = {12/2002}, pages = {1279-1296}, type = {Journal}, keywords = {LTER-MCM, Biggie}, doi = {10.1029/2001WR000834}, url = {http://www.agu.org/pubs/crossref/2002/2001WR000834.shtml}, author = {Michael N. Gooseff and Diane M. McKnight and W. Berry Lyons and Blum, A} } @article {1398, title = {Bacterial dissolved organic carbon demand in antarctic dry valley lakes}, journal = {Limnology and Oceanography}, volume = {46}, year = {2001}, month = {07/2001}, pages = {1189-1194}, type = {Journal}, keywords = {LTER-MCM, Biggie}, doi = {10.4319/lo.2001.46.5.1189}, url = {http://www.jstor.org/stable/2671031}, author = {Cristina D. Takacs-Vesbach and John C. Priscu and Diane M. McKnight} } @mastersthesis {1417, title = {The influence of mixotroph growth on DOM chemistry in Pony Lake, a eutrophic coastal pond in Antarctica}, volume = {M.S.}, year = {2001}, school = {University of Colorado}, type = {masters}, keywords = {LTER-MCM}, doi = {LTER}, author = {Brown, A} } @article {1404, title = {The McMurdo Dry Valleys Long-Term Ecological Research Program: new understanding of the biogeochemistry of the Dry Valley lakes: a review.}, journal = {Polar Geography}, volume = {25}, year = {2001}, pages = {202-217}, keywords = {LTER-MCM}, author = {W. Berry Lyons and Kathleen A. Welch and John C. Priscu and Johanna Laybourn-Parry and Daryl L. Moorhead and Diane M. McKnight and Peter T. Doran and Martyn Tranter} } @phdthesis {1366, title = {Modeling hyporheic exchange influences on biogeochemical processes in dry valley streams, Antarctica}, volume = {Ph.D.}, year = {2001}, school = {University of Colorado}, type = {doctoral}, abstract = {

The ephemeral streams of the Dry Valleys of Antarctica provide habitat to benthic algal mats, and greatly control the quantity and quality of glacial melt water that enters closed basin Dry Valley lakes. Dry Valley watersheds are composed of streambeds and adjacent hyporheic zones. Hydrologic exchange of water and solutes between the stream and the hyporheic zone has the overall effect of increasing residence time in the stream/hyporheic system. Biogeochemical reactions (e.g. chemical weathering, nutrient assimilation) occur both in the water column and in the hyporheic zone. Field experiments and solute transport modeling were employed to elucidate the effects of rapid hyporheic exchange on biogeochemical cycling in Antarctic streams. The results presented here show that (1) large portions of the wetted zone that surrounds each stream is a hyporheic zone, and that stream water exchanges into and out of extended portions of this zone on the order of weeks, (2) the rapid exchange of stream water between the water column and the hyporheic zone controls the rate of weathering in streambed sediments, and (3) denitrification in streams is limited by the conversion of NO2\ to N2O, while the conversion of NO3\ to NO2\ occurs very quickly.

}, keywords = {LTER-MCM}, author = {Michael N. Gooseff} } @mastersthesis {1419, title = {Regrowth of cyanobacterial mats in Greek Creek and the impact of ecotourism}, volume = {M.S.}, year = {2001}, school = {University of Colorado}, type = {masters}, keywords = {LTER-MCM}, doi = {LTER}, author = {Ethan Chatfield} } @article {1406, title = {Retrospective simulation of lake level rise in Lake Bonney based on recent 21-year record: indication of recent climate change in the McMurdo Dry Valleys, Antarctica}, journal = {Journal of Paleolimnology}, volume = {25}, year = {2001}, pages = {477-492}, keywords = {LTER-MCM, Climate Response}, author = {Bomblies, Arne and Diane M. McKnight and Edmund D. Andrews} } @article {1408, title = {Spectrofluorometric characterization of aquatic fulvic acid for determination of precursor organic material and general structural properties.}, journal = {Limnology and Oceanography}, volume = {46}, year = {2001}, pages = {38-48}, keywords = {LTER-MCM}, author = {Diane M. McKnight and Elizabeth W. Boyer and Paul K. Westerhoff and Peter T. Doran and Thomas Kulbe and Dale T. Andersen} } @mastersthesis {1424, title = {Active layer dynamics and hyporheic zone storage in three streams in the McMurdo Dy Valleys, Antarctica}, volume = {M.S.}, year = {2000}, school = {University of Colorado}, type = {masters}, keywords = {LTER-MCM}, doi = {LTER}, author = {Peter A. Conovitz} } @inbook {1426, title = {Climate and hydrologic variations and implications for lake and stream ecological response in the McMurdo Dry Valleys, Antarctica}, booktitle = {Climate Variability and Ecosystem Response at Long Term Ecological Research Sites}, year = {2000}, pages = {174-195}, publisher = {Oxford University Press}, organization = {Oxford University Press}, keywords = {LTER-MCM}, author = {Kathleen A. Welch and W. Berry Lyons and Diane M. McKnight and Chris Jaros and Andrew G Fountain and Thomas H. Nylen and Peter T. Doran and Clive Howard-Williams}, editor = {D. Greenland and D. G. Goodin and R. C. Smith} } @article {1422, title = {Phytoplankton dynamics in a stably stratified Antarctic lake during winter darkness}, journal = {Journal of Phycology}, volume = {36}, year = {2000}, month = {10/2000}, pages = {852-861}, type = {Journal}, keywords = {LTER-MCM, Biggie, winter}, doi = {10.1046/j.1529-8817.2000.00031.x}, author = {Diane M. McKnight and B. L. Howes and C. D. Taylor and D. D. Goehringer} } @article {1421, title = {Stratification and dynamics of microbial loop communities in Lake Fryxell, Antarctica}, journal = {Freshwater Biology}, volume = {44}, year = {2000}, month = {12/2001}, pages = {649-661}, type = {Journal}, keywords = {LTER-MCM, Biggie, protozoa}, doi = {10.1046/j.1365-2427.2000.00612.x}, url = {http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2427.2000.00612.x/abstract}, author = {Emily C. Roberts and Johanna Laybourn-Parry and Diane M. McKnight and Novarino, G} } @article {1456, title = {Dry Valley streams in Antarctica: ecosystems waiting for water}, journal = {Bioscience}, volume = {49}, year = {1999}, pages = {985-995}, keywords = {LTER-MCM}, author = {Diane M. McKnight and Dev K. Niyogi and Alexander S. Alger and Bomblies, Arne and Peter A. Conovitz and Cathy M. Tate} } @article {1447, title = {Physical controls on the Taylor Valley Ecosystem, Antarctica}, journal = {BioScience}, volume = {49}, year = {1999}, month = {12/1999}, pages = {961-972}, type = {Journal}, keywords = {LTER-MCM, Water availability}, author = {Andrew G Fountain and W. Berry Lyons and Melody B. Burkins and Gayle L. Dana and Peter T. Doran and Karen J. Lewis and Diane M. McKnight and Daryl L. Moorhead and Andrew N. Parsons and John C. Priscu and Diana H. Wall and Robert A. Wharton Jr. and Ross A. Virginia} } @article {1481, title = {Analysis of transient storage subject to unsteady flow: diel flow variation in an Antarctic stream}, journal = {Journal of the North American Benthological Society}, volume = {17}, year = {1998}, month = {06/1998}, pages = {143-154}, keywords = {LTER-MCM}, url = {http://www.jstor.org/stable/1467958}, author = {Robert L. Runkel and Diane M. McKnight and Edmund D. Andrews} } @mastersthesis {1537, title = {Climatic controls on streamflow generation from Antarctic glaciers}, volume = {M.S.}, year = {1998}, school = {University of Colorado Boulder}, type = {masters}, address = {Boulder, CO}, keywords = {LTER-MCM}, author = {Bomblies, Arne and Diane M. McKnight} } @inbook {1499, title = {Geochemical Linkages Among Glaciers, Streams, and Lakes Within the Taylor Valley, Antarctica}, booktitle = {Ecosystem Processes in a Polar Desert: The McMurdo Dry Valleys, Antarctica}, volume = {72}, year = {1998}, pages = {77-92}, keywords = {LTER-MCM}, author = {W. Berry Lyons and Kathleen A. Welch and Klaus Neumann and Jeffrey K. Toxey and Robyn McArthur and Changela Williams and Diane M. McKnight and Daryl L. Moorhead} } @inbook {1500, title = {Glaciers of the McMurdo Dry Valleys, Southern Victoria Land, Antarctica}, booktitle = {Ecosystem Processes in a Polar Desert: The McMurdo Dry Valleys, Antarctica}, series = {Antarctic Research Series}, volume = {72}, year = {1998}, pages = {65-75}, keywords = {LTER-MCM}, author = {Andrew G Fountain and Gayle L. Dana and Karen J. Lewis and Bruce H. Vaughn and Diane M. McKnight} } @inbook {1501, title = {Hydrologic Processes Influencing Streamflow Variation in Fryxell Basin, Antarctica}, booktitle = {Ecosystem Processes in a Polar Desert: The McMurdo Dry Valleys, Antarctica}, series = {Antarctic Research Series}, volume = {72}, year = {1998}, pages = {93-108}, keywords = {LTER-MCM}, author = {Peter A. Conovitz and Diane M. McKnight and Lee H. MacDonald and Andrew G Fountain}, editor = {Harold R. House} } @article {1503, title = {A late holocene dessication of Lake Hoare and Lake Fryxell, McMurdo Dry Valleys, Antarctica}, journal = {Antarctic Science}, volume = {10}, year = {1998}, pages = {247-256}, keywords = {LTER-MCM}, author = {W. Berry Lyons and Scott W. Tyler and Robert A. Wharton Jr. and Diane M. McKnight and Bruce H. Vaughn} } @article {1504, title = {Longitudinal Patterns in Algal Abundance and Species Distribution in Meltwater Streams in Taylor Valley, Southern Victoria Land, Antarctica, in Ecosystem Processes in a Polar Desert: The McMurdo Dry Valleys, Antarctica}, journal = {Antarctic Research Series}, volume = {72}, year = {1998}, pages = {109-127}, keywords = {LTER-MCM}, author = {Diane M. McKnight and Alexander S. Alger and Cathy M. Tate and Gordon H Shupe and Sarah A. Spaulding} } @article {1508, title = {McMurdo Dry Valleys LTER: Stream discharge as a function of ambient temperature and incoming shortwave radiation in Taylor Valley, Antarctica}, journal = {Antarctic Journal of the United States - 1996 Review Issue (NSF 98-28)}, volume = {31}, year = {1998}, pages = {196-197}, keywords = {LTER-MCM}, author = {Daryl L. Moorhead and Diane M. McKnight} } @article {1515, title = {Mercury speciation and distribution in a polar desert lake (Lake Hoare, Antarctica) and two glacial meltwater streams}, journal = {Science of the Total Environment}, volume = {213}, year = {1998}, pages = {229-237}, keywords = {LTER-MCM}, author = {Vandal, G.M. and R.P. Mason and Diane M. McKnight and W. Fitzgerald} } @article {1517, title = {Modeling Nitrogen Transformations in Dry Valley Streams, Antarctica, in Ecosystem Processes in a Polar Desert: The McMurdo Dry Valleys, Antarctica}, journal = {Antarctic Research Series}, volume = {72}, year = {1998}, pages = {141-151}, keywords = {LTER-MCM}, author = {Daryl L. Moorhead and Diane M. McKnight and Cathy M. Tate} } @article {1546, title = {Canada Stream: a glacial meltwater stream in Taylor Valley, South Victoria Land, Antarctica}, journal = {Journal of the North American Benthological Society}, volume = {16}, year = {1997}, pages = {14-17}, keywords = {LTER-MCM}, author = {Diane M. McKnight and Cathy M. Tate} } @inbook {1549, title = {Chemical weathering rates and reactions in the Lake Fryxell Basin, Taylor Valley : Comparison to temperate river basins}, booktitle = {Ecosystem Processes in Antarctic Ice-free Landscapes}, year = {1997}, pages = {147-154}, publisher = {Balkema Press, Rotterdam}, organization = {Balkema Press, Rotterdam}, keywords = {LTER-MCM}, author = {W. Berry Lyons and Kathleen A. Welch and C. A. Nezat and K. Crick and Jeffrey K. Toxey and J.A. Mastrine and Diane M. McKnight} } @article {1553, title = {Diatoms in sediments of perennially ice-covered Lake Hoare, and implications for interpreting lake history in the McMurdo Dry Valleys of Antarctica}, journal = {Journal of Paleolimnology}, volume = {17}, year = {1997}, pages = {403-420}, keywords = {LTER-MCM}, author = {Sarah A. Spaulding and Diane M. McKnight and E.F. Stoermer and Peter T. Doran} } @inbook {1554, title = {Ecological processes in a cold desert ecosystem: the abundance and species distribution of algal mats in glacial meltwater streams in Taylor Valley}, booktitle = {Institute of Arctic and Alpine Research}, series = {Occasional Paper}, volume = {51}, year = {1997}, pages = {108 pp}, publisher = {University of Colorado}, organization = {University of Colorado}, keywords = {LTER-MCM}, url = {http://instaar.colorado.edu/other/download/OP51-ECOLOGICAL-PROCESSES.pdf}, author = {Alexander S. Alger and Diane M. McKnight and Sarah A. Spaulding and Cathy M. Tate}, editor = {Gordon H Shupe and Kathleen A. Welch and R. L. Edwards and Edmund D. Andrews} } @article {1560, title = {The microbial plankton of Lake Fryxell, southern Victoria Land, Antarctica during the summers of 1992 and 1994}, journal = {Polar Biology}, volume = {17}, year = {1997}, pages = {54-61}, keywords = {LTER-MCM}, author = {Johanna Laybourn-Parry and Mark R. James and Diane M. McKnight and John C. Priscu and Sarah A. Spaulding and Russell Shiel} } @inbook {1564, title = {Species composition and primary production of algal communities in Dry Valley streams in Antarctica: Examination of the functional role of biodiversity}, booktitle = {Ecosystem Processes in Antarctic Ice-free Landscapes}, year = {1997}, pages = {171-179}, publisher = {Balkema Press, Rotterdam}, organization = {Balkema Press, Rotterdam}, keywords = {LTER-MCM}, author = {Dev K. Niyogi and Cathy M. Tate and Diane M. McKnight and John H. Duff and Alexander S. Alger} } @article {1574, title = {Geochemistry of aquatic humic substances in the Lake Fryxell Basin, Antarctica}, journal = {Biogeochemistry}, volume = {34}, year = {1996}, pages = {157-188}, keywords = {LTER-MCM}, author = {George R. Aiken and Diane M. McKnight and Richard A. Harnish and Robert Wershaw} } @article {1587, title = {The influence of stream channel characteristics on streamflow and annual water budgets for lakes in Taylor Valley}, journal = {Antarctic Journal of the U.S.}, volume = {30}, year = {1995}, pages = {284-287}, keywords = {LTER-MCM}, author = {Harold R. House and Diane M. McKnight and Paul Von Guerard} } @article {1589, title = {McMurdo LTER: Algal mat distribution in glacial meltwater streams in Taylor Valley, southern Victoria Land, Antarctica}, journal = {Antarctic Journal of the United States}, volume = {30}, year = {1995}, pages = {287-289}, keywords = {LTER-MCM}, author = {Diane M. McKnight and Cathy M. Tate} } @article {1594, title = {McMurdo LTER: Species composition and spatial distribution of algal mats in Green Creek, Taylor Valley, Antarctica}, journal = {Antarctic Journal of the U. S.}, volume = {30}, year = {1995}, pages = {289-291}, keywords = {LTER-MCM}, author = {Alexander S. Alger and Sarah A. Spaulding and Gordon H Shupe and Diane M. McKnight} } @article {1606, title = {Streamflow, water-temperature, and specific-conductance data for selected streams draining into Lake Fryxell, Lower Taylor Valley, Victoria Land, Antarctica, 1990-92}, journal = {U.S. Geological Survey. Open-File Report 94-545}, year = {1995}, keywords = {LTER-MCM}, author = {Paul Von Guerard and Diane M. McKnight and Richard A. Harnish and J. W. Gartner and Edmund D. Andrews} } @article {1611, title = {Aquatic fulvic acids in algal-rich antarctic ponds}, journal = {Limnology and Oceanography}, volume = {39}, year = {1994}, month = {07/1994}, pages = {1972-1979}, keywords = {LTER-MCM, Biggie}, author = {Diane M. McKnight and Edmund D. Andrews and Sarah A. Spaulding and George R. Aiken} } @article {1617, title = {McMurdo LTER: Inorganic geochemical studies with special reference to calcium carbonate dynamics}, journal = {Antarctic Journal of the U.S.}, volume = {29}, year = {1994}, pages = {237-239}, keywords = {LTER-MCM}, author = {Kathleen A. Welch and W. Berry Lyons and John C. Priscu and R. L. Edwards and Diane M. McKnight and Harold R. House and Robert A. Wharton Jr.} } @article {1620, title = {McMurdo LTER: Streamflow Measurements in Taylor Valley}, journal = {Antarctic Journal of the United States}, volume = {29}, year = {1994}, pages = {230-232}, keywords = {LTER-MCM}, author = {Diane M. McKnight and Harold R. House and Paul Von Gerard} } @article {1627, title = {Phytoplankton population dynamics in perennially ice-covered Lake Fryxell, Antarctica}, journal = {Journal of Plankton Research}, volume = {16}, year = {1994}, pages = {527-541}, keywords = {LTER-MCM}, author = {Sarah A. Spaulding and Diane M. McKnight and Richard L. Smith and Richard Dufford} } @article {1632, title = {Dissolved Organic Material in Dry Valley Lakes: A Comparison of Lake Fryxell, Lake Hoare, and Lake Vanda, in Physical and Biogeochemical Processes in Antarctic Lakes}, journal = {Antarctic Research Series}, volume = {59}, year = {1993}, pages = {119-133}, keywords = {LTER-MCM}, author = {Diane M. McKnight and George R. Aiken and Edmund D. Andrews and E. C. Bowles and Richard A. Harnish} } @article {1644, title = {Potential hydrologic and geochemical consequences of the 1992 merging of Lake Chad with Lake Hoare in Taylor Valley}, journal = {Antarctic Journal of the U.S.}, volume = {28}, year = {1993}, pages = {249-251}, keywords = {LTER-MCM}, author = {Diane M. McKnight and Edmund D. Andrews} }