@article {4928, title = {Remotely characterizing photosynthetic biocrust in snowpack-fed microhabitats of Taylor Valley, Antarctica}, journal = {Science of Remote Sensing}, year = {2024}, month = {02/2024}, pages = {100120}, abstract = {

Microbial communities are the primary drivers of carbon cycling in the McMurdo Dry Valleys of Antarctica. Dense microbial mats, consisting mainly of photosynthetic cyanobacteria, occupy aquatic areas associated with streams and lakes. Other microbial communities also occur at lower densities as patchy surface biological soil crusts (hereafter, biocrusts) across the terrestrial landscape. Multispectral satellite data have been used to model microbial mat abundance in high-density areas like stream and lake margins, but no previous studies have investigated the lower detection limits of biocrusts. Here, we describe remote sensing and field-based survey and sampling approaches to study the detectability and distribution of biocrusts in the McMurdo Dry Valleys. Using a combination of multi- and hyperspectral tools and spectral linear unmixing, we modeled the abundances of biocrust in eastern Taylor Valley. Our spectral approaches can detect low masses of biocrust material in laboratory microcosms down to biocrust concentrations of 1\% by mass. These techniques also distinguish the spectra of biocrust from both surface rock and mineral signatures from orbit. We found that biocrusts are present throughout the soils of eastern Taylor Valley and are associated with diverse underlying soil communities. The densest biocrust communities identified in this study had total organic carbon 5x greater than the content of typical arid soils. The most productive biocrusts were located downslope of melting snowpacks in unique soil ecosystems that are distinct from the surrounding arid landscape. There are similarities between the snowpack and stream sediment communities (high diversity of soil invertebrates) as well as their ecosystem properties (e.g., persistence of liquid water, high transfer of available nutrients, lower salinity from flushing) compared to the typical arid terrestrial ecosystem of the dry valleys. Our approach extends the capability of orbital remote sensing of photosynthetic communities out of the aquatic margins and into the drier soils which comprise most of this landscape. This interdisciplinary work is critical for measuring and monitoring terrestrial carbon stocks and predicting future ecosystem dynamics in this currently water-limited but increasingly dynamic Antarctic landscape, which is particularly climate-sensitive and difficult to access.

}, keywords = {LTER-MCM, Antarctica, biocrust, carbon, reflectance spectroscopy, snow, soil ecology}, issn = {26660172}, doi = {10.1016/j.srs.2024.100120}, url = {https://www.sciencedirect.com/science/article/pii/S266601722400004X}, author = {Power, Sarah N. and Salvatore, Mark R. and Eric R. Sokol and Lee F. Stanish and Borges, Schuyler R. and Byron Adams and John E. Barrett} } @article {4935, title = {Sentinel protist taxa of the McMurdo Dry Valley lakes, Antarctica: A review}, journal = {Frontiers in Ecology and Evolution}, volume = {12}, year = {2024}, month = {03/2024}, pages = {1323472}, abstract = {

High-latitude meromictic lakes such as those in the Antarctic McMurdo Dry Valleys (MDV) harbor aquatic ecosystems dominated by the microbial loop. Within this habitat, which is limited year-round by light and nutrients, protists, or single celled eukaryotes, play outsized roles in the food web as the dominant primary producers and the apex predators. Thus, the MDV lake ecosystem represents an ideal system to study the role of sentinel protist taxa in carbon and nutrient cycling. The perennially ice-covered lakes are part of the McMurdo Long Term Ecological Research (McM LTER; mcmlter.org) established in 1993. In this review we will highlight the diversity and trophic roles of the MDV lake protist community and compare environmental factors driving spatiotemporal patterns in key protist taxa in two lakes within the McM LTER, Lakes Bonney and Fryxell. We will then discuss lessons learned from manipulated experiments on the impact of current and future climate-driven environmental change on sensitive protist taxa. Last, we will integrate knowledge gained from 25 years of lab-controlled experiments on key photosynthetic protists to extend our understanding of the function of these extremophiles within the MDV aquatic food webs. Our research group has studied the distribution and function of the MDV microbial community for nearly two decades, training the next generation of scientists to tackle future problems of these globally significant microbes. This review article will also highlight early career scientists who have contributed to this body of work and represent the future of scientific understanding in the Anthropocene.

}, keywords = {LTER-MCM, Antarctica, Disturbance, McMurdo Dry Valley lakes, phytoplankton, protist}, doi = {10.3389/fevo.2024.1323472}, url = {https://www.frontiersin.org/articles/10.3389/fevo.2024.1323472}, author = {Rachael M. Morgan-Kiss and Popson, Devon and Pereira, Rochelle and Dolhi-Binder, J and Teufel, Amber G. and Li, Wei and Kalra, Isha and Sherwell, Shasten S. and Reynebeau, Emily and Cristina D. Takacs-Vesbach} } @article {4937, title = {High salt-induced PSI-supercomplex is associated with high CEF and attenuation of state transitions}, journal = {Photosynthesis Research}, volume = {157}, year = {2023}, month = {09/2023}, pages = {65 - 84}, abstract = {

While PSI-driven cyclic electron flow (CEF) and assembly of thylakoid supercomplexes have been described in model organisms like Chlamydomonas reinhardtii, open questions remain regarding their contributions to survival under long-term stress. The Antarctic halophyte, C. priscuii UWO241 (UWO241), possesses constitutive high CEF rates and a stable PSI-supercomplex as a consequence of adaptation to permanent low temperatures and high salinity. To understand whether CEF represents a broader acclimation strategy to short- and long-term stress, we compared high salt acclimation between the halotolerant UWO241, the salt-sensitive model, C. reinhardtii, and a moderately halotolerant Antarctic green alga, C. sp. ICE-MDV (ICE-MDV). CEF was activated under high salt and associated with increased non-photochemical quenching in all three Chlamydomonas species. Furthermore, high salt-acclimated cells of either strain formed a PSI-supercomplex, while state transition capacity was attenuated. How the CEF-associated PSI-supercomplex interferes with state transition response is not yet known. We present a model for interaction between PSI-supercomplex formation, state transitions, and the important role of CEF for survival during long-term exposure to high salt.

}, keywords = {LTER-MCM, acclimation, Antarctica, Chlamydomonas, Cyclic electron flow, PSI-supercomplex, salinity, state transitions}, issn = {0166-8595}, doi = {10.1007/s11120-023-01032-y}, url = {https://link.springer.com/10.1007/s11120-023-01032-y}, author = {Kalra, Isha and Wang, Xin and Zhang, Ru and Rachael M. Morgan-Kiss} } @phdthesis {4862, title = {Microbial life in challenging environments}, volume = {Ph.D.}, year = {2023}, school = {University of Colorado Boulder}, type = {doctoral}, address = {Boulder, CO}, abstract = {

Microorganisms are nearly ubiquitous on Earth, but the identity and function of microbial communities are inherently dependent on the properties of the specific environment in question. Here, I have studied soils around the world to answer questions about how the functional attributes of microorganisms allow them to respond to challenging environmental conditions. First, I explore how microbial communities in soils change across environmental gradients in Antarctica. I show that microbes in Antarctic surface soils are most restricted by low temperatures, low water availability, and high concentrations of salt. Microbial communities near the polar plateau, the most challenging environment, are dominated by Actinobacteria and Chloroflexi, and are enriched in genes associated with the oxidation of hydrogen gas as an energy source. Second, I show that the earliest microbial colonizers of a newly-formed volcanic island in the Kingdom of Tonga are chemolithotrophs that appear to have come from nearby geothermal systems. While many of these microbes utilize sulfur as an energy source, the most abundant organisms have genes that indicate they can oxidize trace gases including carbon monoxide and hydrogen. Finally, I show that organisms associated with carbon limited subsurface soils tend to have smaller genomes, grow more slowly, and have more gene pathways associated with metabolism and the storage of carbon. Taken together, these studies shed light on microbial survival in challenging soil environments and show the varied ways in which microbial communities interact with and are affected by their surroundings.

}, keywords = {LTER-MCM, Antarctica, environmental conditions, microbial ecology, microorganisms, soils, tonga}, url = {https://www.proquest.com/docview/2814734209}, author = {Dragone, Nicholas B.}, editor = {Noah Fierer} } @article {4840, title = {Temperature response of metabolic activity of an Antarctic nematode}, journal = {Biology}, volume = {12}, year = {2023}, month = {01/2023}, pages = {109}, abstract = {

Because of climate change, the McMurdo Dry Valleys of Antarctica (MCM) have experienced an increase in the frequency and magnitude of summer pulse warming and surface ice and snow melting events. In response to these environmental changes, some nematode species in the MCM have experienced steady population declines over the last three decades, but Plectus murrayi, a mesophilic nematode species, has responded with a steady increase in range and abundance. To determine how P. murrayi responds to increasing temperatures, we measured metabolic heat and CO2 production rates and calculated O2 consumption rates as a function of temperature at 5 \°C intervals from 5 to 50 \°C. Heat, CO2 production, and O2 consumption rates increase approximately exponentially up to 40 \°C, a temperature never experienced in their polar habitat. Metabolic rates decline rapidly above 40 \°C and are irreversibly lost at 50 \°C due to thermal stress and mortality. Caenorhabditis elegans, a much more widespread nematode that is found in more temperate environments reaches peak metabolic heat rate at just 27 \°C, above which it experiences high mortality due to thermal stress. At temperatures from 10 to 40 \°C, P. murrayi produces about 6 times more CO2 than the O2 it consumes, a respiratory quotient indicative of either acetogenesis or de novo lipogenesis. No potential acetogenic microbes were identified in the P. murrayi microbiome, suggesting that P. murrayi is producing increased CO2 as a byproduct of de novo lipogenesis. This phenomenon, in conjunction with increased summer temperatures in their polar habitat, will likely lead to increased demand for carbon and subsequent increases in CO2 production, population abundance, and range expansion. If such changes are not concomitant with increased carbon inputs, we predict the MCM soil ecosystems will experience dramatic declines in functional and taxonomic diversity.

}, keywords = {LTER-MCM, Antarctica, carbon cycling, climate change, nematode, respiration rates, soil temperature}, doi = {10.3390/biology12010109}, url = {https://www.mdpi.com/2079-7737/12/1/109}, author = {Robinson, Colin Michael and Hansen, Lee D. and Xue, Xia and Adams, Byron J.} } @article {4766, title = {Cyclic electron flow (CEF) and ascorbate pathway activity provide constitutive photoprotection for the photopsychrophile, Chlamydomonas sp. UWO 241~(renamed Chlamydomonas priscuii)}, journal = {Photosynthesis Research}, volume = {151}, year = {2022}, month = {03/2022}, pages = {235 - 250}, abstract = {

Under environmental stress, plants and algae employ a variety of strategies to protect the photosynthetic apparatus and maintain photostasis. To date, most studies on stress acclimation have focused on model organisms which possess limited to no tolerance to stressful extremes. We studied the ability of the Antarctic alga Chlamydomonas sp. UWO 241 (UWO 241) to acclimate to low temperature, high salinity or high light. UWO 241 maintained robust growth and photosynthetic activity at levels of temperature (2 \°C) and salinity (700 mM NaCl) which were nonpermissive for a mesophilic sister species, Chlamydomonas raudensis SAG 49.72 (SAG 49.72). Acclimation in the mesophile involved classic mechanisms, including downregulation of light harvesting and shifts in excitation energy between photosystem I and II. In contrast, UWO 241 exhibited high rates of PSI-driven cyclic electron flow (CEF) and a larger capacity for nonphotochemical quenching (NPQ). Furthermore, UWO 241 exhibited constitutively high activity of two key ascorbate cycle enzymes, ascorbate peroxidase and glutathione reductase and maintained a large ascorbate pool. These results matched the ability of the psychrophile to maintain low ROS under short-term photoinhibition conditions. We conclude that tight control over photostasis and ROS levels are essential for photosynthetic life to flourish in a native habitat of permanent photooxidative stress. We propose to rename this organism Chlamydomonas priscuii.

}, keywords = {LTER-MCM, Antarctica, ascorbate, Cyclic electron flow, Photosystem I, Psychrophile, ROS}, doi = {10.1007/s11120-021-00877-5}, url = {https://link.springer.com/article/10.1007/s11120-021-00877-5}, author = {Stahl-Rommel, Sarah and Kalra, Isha and D{\textquoteright}Silva, Susanna and Hahn, Mark M. and Popson, Devon and Cvetkovska, Marina and Rachael M. Morgan-Kiss} } @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 {4836, title = {A draft mitogenome of Plectus murrayi}, journal = {Journal of Nematology}, volume = {54}, year = {2022}, month = {02/2022}, abstract = {

Plectus murrayi is a free-living microbivorous nematode endemic to Antarctic soils. Our draft assembly of its mitogenome was 15,656 bp long, containing 12 protein-coding, eight transfer RNA (tRNA), and two ribosomal RNA (rRNA) genes. Mitophylogenomic analyses extend our understanding of mitochondrial evolution in Nematoda

}, keywords = {LTER-MCM, Antarctica, genome decay, genomics, mitochondrial genome, MitoZ, phylogeny}, doi = {10.2478/jofnem-2022-0035}, url = {https://www.sciendo.com/article/10.2478/jofnem-2022-0035https://www.sciendo.com/pdf/10.2478/jofnem-2022-0035}, author = {Xue, Xia and Adams, Byron J. and Dilman, Adler R.} } @thesis {4835, title = {Effect of climate history on the genetic structure of an Antarctic soil nematode}, volume = {MS}, year = {2022}, month = {12/2022}, school = {Brigham Young University}, type = {Master{\textquoteright}s thesis}, address = {Provo, UT, USA}, abstract = {

Historical climate disturbances such as glacial cycling and fluctuating stream, lake, and sea levels strongly influence the distribution and evolutionary trajectories of Antarctic terrestrial species. Antarctic invertebrates, with limited long-range mobility, including the ubiquitous sentinel nematode species Scottnema lindsayae, are especially sensitive to climate disturbances. We tested hypotheses associated with the historical geographic and population genetic structure of this species as it occurs across the McMurdo Dry Valleys (MDVs) of Antarctica. In order to reconstruct the influence of climate disturbance and ecological conditions on this species, partial mitochondrial COI gene sequences were sequenced and analyzed from individual S. lindsayae collected from sites across the MDVs reflecting a opposing gradients of climate disturbance during the Last Glacial Maximum (LGM). We found that populations were strongly geomorphic barriers with distinct haplotypes associated with valleys except among valleys that experienced glacial advance and retreat during the LGM. One monophyletic clade corresponds with valley systems that were undisturbed during the LGM indicating putative refugia areas. A second monophyletic clade corresponds to recent dispersal and expansion of evolutionarily younger populations into valleys that were strongly reworked by glacial activity during the LGM. Our work shows that contemporary populations of these animals are strongly structured by prior climate history. Such findings can be useful for interpreting long-term monitoring of demographic shifts of soil organisms in response to changing climate trends in the McMurdo Dry Valleys.

}, keywords = {LTER-MCM, Antarctica, biogeography, climate disturbance, evolution, McMurdo Dry Valleys, polar, population genetics}, url = {http://hdl.lib.byu.edu/1877/etd12622}, author = {Jackson, Abigail C.}, editor = {Adams, Byron J.} } @article {4718, title = {Elevational constraints on the composition and genomic attributes of microbial communities in Antarctic soils}, journal = {mSystems}, volume = {7}, year = {2022}, month = {01/2022}, pages = {e01330-21}, abstract = {

The inland soils found on the Antarctic continent represent one of the more challenging environments for microbial life on Earth. Nevertheless, Antarctic soils harbor unique bacterial and archaeal (prokaryotic) communities able to cope with extremely cold and dry conditions. These communities are not homogeneous, and the taxonomic composition and functional capabilities (genomic attributes) of these communities across environmental gradients remain largely undetermined. We analyzed the prokaryotic communities in soil samples collected from across the Shackleton Glacier region of Antarctica by coupling quantitative PCR, marker gene amplicon sequencing, and shotgun metagenomic sequencing. We found that elevation was the dominant factor explaining differences in the structures of the soil prokaryotic communities, with the drier and saltier soils found at higher elevations harboring less diverse communities and unique assemblages of cooccurring taxa. The higher-elevation soil communities also had lower maximum potential growth rates (as inferred from metagenome-based estimates of codon usage bias) and an overrepresentation of genes associated with trace gas metabolism. Together, these results highlight the utility of assessing community shifts across pronounced environmental gradients to improve our understanding of the microbial diversity found in Antarctic soils and the strategies used by soil microbes to persist at the limits of habitability.

}, keywords = {LTER-MCM, Antarctica, microbial ecology, soil microbiology, soils}, doi = {10.1128/msystems.01330-21}, url = {https://journals.asm.org/doi/full/10.1128/msystems.01330-21}, author = {Dragone, Nicholas B. and Henley, Jessica B. and Holland-Moritz, Hannah and Melisa A. Diaz and Hogg, Ian D. and W. Berry Lyons and Diana H. Wall and Byron Adams and Noah Fierer}, editor = {Mackelprang, Rachel} } @article {4825, title = {Glacial legacies: Microbial communities of Antarctic refugia}, journal = {Biology}, volume = {11}, year = {2022}, month = {10/2022}, pages = {1440}, abstract = {

In the cold deserts of the McMurdo Dry Valleys (MDV) the suitability of soil for microbial life is determined by both contemporary processes and legacy effects. Climatic changes and accompanying glacial activity have caused local extinctions and lasting geochemical changes to parts of these soil ecosystems over several million years, while areas of refugia may have escaped these disturbances and existed under relatively stable conditions. This study describes the impact of historical glacial and lacustrine disturbance events on microbial communities across the MDV to investigate how this divergent disturbance history influenced the structuring of microbial communities across this otherwise very stable ecosystem. Soil bacterial communities from 17 sites representing either putative refugia or sites disturbed during the Last Glacial Maximum (LGM) (22\–17 kya) were characterized using 16 S metabarcoding. Regardless of geographic distance, several putative refugia sites at elevations above 600 m displayed highly similar microbial communities. At a regional scale, community composition was found to be influenced by elevation and geographic proximity more so than soil geochemical properties. These results suggest that despite the extreme conditions, diverse microbial communities exist in these putative refugia that have presumably remained undisturbed at least through the LGM. We suggest that similarities in microbial communities can be interpreted as evidence for historical climate legacies on an ecosystem-wide scale.

}, keywords = {LTER-MCM, Antarctica, McMurdo Dry Valleys, metabarcoding, microbial communities, refugia, soil biodiversity}, doi = {10.3390/biology11101440}, url = {https://www.mdpi.com/2079-7737/11/10/1440}, author = {Jackson, Abigail C. and Jorna, Jesse and Chaston, J and Adams, Byron J.} } @article {4817, title = {Islands in the ice: Potential impacts of habitat transformation on Antarctic biodiversity}, journal = {Global Change Biology}, year = {2022}, month = {07/2022}, abstract = {

Antarctic biodiversity faces an unknown future with a changing climate. Most terrestrial biota is restricted to limited patches of ice-free land in a sea of ice, where they are adapted to the continent\&$\#$39;s extreme cold and wind and exploit microhabitats of suitable conditions. As temperatures rise, ice-free areas are predicted to expand, more rapidly in some areas than others. There is high uncertainty as to how species\&$\#$39; distributions, physiology, abundance, and survivorship will be affected as their habitats transform. Here we use current knowledge to propose hypotheses that ice-free area expansion (i) will increase habitat availability, though the quality of habitat will vary; (ii) will increase structural connectivity, although not necessarily increase opportunities for species establishment; (iii) combined with milder climates will increase likelihood of non-native species establishment, but may also lengthen activity windows for all species; and (iv) will benefit some species and not others, possibly resulting in increased homogeneity of biodiversity. We anticipate considerable spatial, temporal, and taxonomic variation in species responses, and a heightened need for interdisciplinary research to understand the factors associated with ecosystem resilience under future scenarios. Such research will help identify at-risk species or vulnerable localities and is crucial for informing environmental management and policymaking into the future.

}, keywords = {LTER-MCM, Antarctica, biodiversity, biotic homogenization, climate change, connectivity, ice-free, non-native species}, doi = {10.1111/gcb.16331}, url = {https://onlinelibrary.wiley.com/doi/10.1111/gcb.16331}, author = {Lee, Jasmine R. and Waterman, Melinda J. and Shaw, Justine D. and Bergstrom, Dana M. and Lynch, Heather J. and Diana H. Wall and Robinson, Sharon A.} } @article {4759, title = {Limits to the three domains of life: Lessons from community assembly along an Antarctic salinity gradient}, journal = {Extremophiles}, volume = {26}, year = {2022}, month = {04/2022}, pages = {15}, abstract = {

Extremophiles exist among all three domains of life; however, physiological mechanisms for surviving harsh environmental conditions differ among Bacteria, Archaea and Eukarya. Consequently, we expect that domain-specific variation of diversity and community assembly patterns exist along environmental gradients in extreme environments. We investigated inter-domain community compositional differences along a high-elevation salinity gradient in the McMurdo Dry Valleys, Antarctica. Conductivity for 24 soil samples collected along the gradient ranged widely from 50 to 8355 \µS cm-1. Taxonomic richness varied among domains, with a total of 359 bacterial, 2 archaeal, 56 fungal, and 69 non-fungal eukaryotic operational taxonomic units (OTUs). Richness for bacteria, archaea, fungi, and non-fungal eukaryotes declined with increasing conductivity (all P\ \<\ 0.05). Principal coordinate ordination analysis (PCoA) revealed significant (ANOSIM R\ =\ 0.97) groupings of low/high salinity bacterial OTUs, while OTUs from other domains were not significantly clustered. Bacterial beta diversity was unimodally distributed along the gradient and had a nested structure driven by species losses, whereas in fungi and non-fungal eukaryotes beta diversity declined monotonically without strong evidence of nestedness. Thus, while increased salinity acts as a stressor in all domains, the mechanisms driving community assembly along the gradient differ substantially between the domains.

}, keywords = {LTER-MCM, Antarctica, inter-domain response, McMurdo Dry Valleys, salinity, species richness patterns}, doi = {10.1007/s00792-022-01262-3}, url = {https://link.springer.com/article/10.1007/s00792-022-01262-3}, author = {Jiang, Xiaoben and David J. Van Horn and Okie, Jordan G. and Heather N. Buelow and Schwartz, Egbert and Colman, Daniel R. and Feeser, Kelli L. and Cristina D. Takacs-Vesbach} } @article {4834, title = {Lipid biomarkers from microbial mats on the McMurdo Ice Shelf, Antarctica: Signatures for life in the cryosphere}, journal = {Frontiers in Microbiology}, volume = {13}, year = {2022}, month = {06/2022}, pages = {903621}, abstract = {

Persistent cold temperatures, a paucity of nutrients, freeze-thaw cycles, and the strongly seasonal light regime make Antarctica one of Earth\’s least hospitable surface environments for complex life. Cyanobacteria, however, are well-adapted to such conditions and are often the dominant primary producers in Antarctic inland water environments. In particular, the network of meltwater ponds on the \‘dirty ice\’ of the McMurdo Ice Shelf is an ecosystem with extensive cyanobacteria-dominated microbial mat accumulations. This study investigated intact polar lipids (IPLs), heterocyte glycolipids (HGs), and bacteriohopanepolyols (BHPs) in combination with 16S and 18S rRNA gene diversity in microbial mats of twelve ponds in this unique polar ecosystem. To constrain the effects of nutrient availability, temperature and freeze-thaw cycles on the lipid membrane composition, lipids were compared to stromatolite-forming cyanobacterial mats from ice-covered lakes in the McMurdo Dry Valleys as well as from (sub)tropical regions and hot springs. The 16S rRNA gene compositions of the McMurdo Ice Shelf mats confirm the dominance of Cyanobacteria and Proteobacteria while the 18S rRNA gene composition indicates the presence of Ochrophyta, Chlorophyta, Ciliophora, and other microfauna. IPL analyses revealed a predominantly bacterial community in the meltwater ponds, with archaeal lipids being barely detectable. IPLs are dominated by glycolipids and phospholipids, followed by aminolipids. The high abundance of sugar-bound lipids accords with a predominance of cyanobacterial primary producers. The phosphate-limited samples from the (sub)tropical, hot spring, and Lake Vanda sites revealed a higher abundance of aminolipids compared to those of the nitrogen-limited meltwater ponds, affirming the direct affects that N and P availability have on IPL compositions. The high abundance of polyunsaturated IPLs in the Antarctic microbial mats suggests that these lipids provide an important mechanism to maintain membrane fluidity in cold environments. High abundances of HG keto-ols and HG keto-diols, produced by heterocytous cyanobacteria, further support these findings and reveal a unique distribution compared to those from warmer climates.

}, keywords = {LTER-MCM, Antarctica, bacteriohopanepolyol, cyanobacteria, heterocyte glycolipids, homeoviscous adaptation, intact polar lipid, microbial mats}, doi = {10.3389/fmicb.2022.90362110.3389/fmicb.2022.903621.s001}, url = {https://www.frontiersin.org/articles/10.3389/fmicb.2022.903621/full}, author = {Evans, Thomas W. and Kalambokidis, Maria J. and Jungblut, Anne D. and Millar, Jasmin L. and Bauersachs, Thorsten and Grotheer, Hendrik and Mackey, Tyler J. and Ian Hawes and Summons, Roger E.} } @article {4777, title = {Long-term stream hydrology and meteorology of a polar desert, the McMurdo Dry Valleys, Antarctica}, journal = {Hydrological Processes}, volume = {36}, year = {2022}, month = {06/2022}, pages = {e14623}, abstract = {

The McMurdo Dry Valleys (MDVs; 77.50\°S, 162.25\°E) make up the largest ice-free region of Antarctica at 3500 km2. Their position near the coast of the Ross Sea provides for a milder climate than much of the rest of the continent. Alpine and piedmont glaciers in the MDVs melt during the austral summer providing water to down gradient streams and terminal lakes on valley floors. There are currently 14 meteorological stations and 17 stream gauges operating across the MDVs, some with continuous records that go back to 1969. This relatively high density of monitoring stations reflects the fact that glaciers of different sizes and elevation ranges are the main source of water to streams. Thus, each glacier represents a different watershed. The bulk of these records start in the late 1980s/early 1990s. These data collection activities directly support research endeavors of the McMurdo Dry Valleys Long Term Ecological Research project, as well as a host of other science groups working in the MDVs. As such, both real time data and archived data from these sites is available through the online database interface of the project (https://mcmlter.org).

}, keywords = {LTER-MCM, Antarctica, LTER, McMurdo Dry Valleys, meltwater streams, polar desert, research catchment}, issn = {0885-6087}, doi = {10.1002/hyp.14623}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/hyp.14623}, author = {Gooseff, Michael N. and McKnight, Diane M. and Doran, Peter T. and Fountain, Andrew} } @article {4776, title = {Organic matter distribution in the icy environments of Taylor Valley, Antarctica}, journal = {Science of The Total Environment}, volume = {841}, year = {2022}, month = {10/2022}, pages = {156639}, abstract = {

Glaciers can accumulate and release organic matter affecting the structure and function of associated terrestrial and aquatic ecosystems. We analyzed 18 ice cores collected from six locations in Taylor Valley (McMurdo Dry Valleys), Antarctica to determine the spatial abundance and quality of organic matter, and the spatial distribution of bacterial density and community structure from the terminus of the Taylor Glacier to the coast (McMurdo Sound). Our results showed that dissolved and particulate organic carbon (DOC and POC) concentrations in the ice core samples increased from the Taylor Glacier to McMurdo Sound, a pattern also shown by bacterial cell density. Fluorescence Excitation Emission Matrices Spectroscopy (EEMs) and multivariate parallel factor (PARAFAC) modeling identified one humic-like (C1) and one protein-like (C2) component in ice cores whose fluorescent intensities all increased from the Polar Plateau to the coast. The fluorescence index showed that the bioavailability of dissolved organic matter (DOM) also decreased from the Polar Plateau to the coast. Partial least squares path modeling analysis revealed that bacterial abundance was the main positive biotic factor influencing both the quantity and quality of organic matter. Marine aerosol influenced the spatial distribution of DOC more than katabatic winds in the ice cores. Certain bacterial taxa showed significant correlations with DOC and POC concentrations. Collectively, our results show the tight connectivity among organic matter spatial distribution, bacterial abundance and meteorology in the McMurdo Dry Valley ecosystem.

}, keywords = {LTER-MCM, Antarctica, bacteria, ice cores, katabatic wind, marine aerosol, organic matter}, issn = {00489697}, doi = {10.1016/j.scitotenv.2022.156639}, url = {https://www.sciencedirect.com/science/article/abs/pii/S0048969722037366}, author = {Guo, Bixi and Li, Wei and Santib{\'a}{\~n}ez, Pamela and John C. Priscu and Liu, Yongqin and Liu, Keshao} } @article {4945, title = {Timing and duration of ephemeral Antarctic water tracks and wetlands using high temporal{\textendash}resolution satellite imagery, high spatial{\textendash}resolution satellite imagery, and ground-based sensors in the McMurdo Dry Valleys}, journal = {Arctic, Antarctic, and Alpine Research}, volume = {54}, year = {2022}, month = {12/2022}, pages = {538 - 561}, abstract = {

Antarctic water tracks and ephemeral wetlands are a primary location for biogeochemical soil processes driving cold desert soil formation. Though the spatial extent of water tracks and wetted soils has been mapped in the McMurdo Dry Valleys (MDV) on the basis of mapping darkened pixels in high-resolution commercial satellite imagery, the timescale over which water tracks and wetlands form and the duration of these biogeochemically active environments remain unknown. Here, we determine the start date and end dates and the duration of wetted soils at ten sites located across the MDV using a combination of in situ soil sensors and two complementary remote imaging platforms (Planet and WorldView) to understand the hydroclimatic processes that drive water track and wetland formation. Our remote sensing employs a terrain correction workflow that removes the contribution of differential direct illumination and small-scale shadowing on pixel brightness, reducing false positives (soils identified as wetted when in fact they are shadowed or darkened as a consequence of high phase angle). Our findings extend the water track and wetland hydroperiod by over a month, showing darkening occurring from November to March, suggesting hydrological contributions from ground ice thaw, snowmelt, and salt deliquescence and soil brine growth.

}, keywords = {LTER-MCM, Antarctica, hydroperiod, remote sensing, water track, wetland}, issn = {1523-0430}, doi = {10.1080/15230430.2022.2123858}, url = {https://www.tandfonline.com/doi/full/10.1080/15230430.2022.2123858}, author = {Kuentz, Lily C. and Joseph S. Levy and Salvatore, Mark R.} } @article {4585, title = {Antarctic water tracks: Microbial community responses to variation in soil moisture, pH, and salinity}, journal = {Frontiers in Microbiology}, volume = {12}, year = {2021}, month = {01/2021}, abstract = {

Ice-free soils in the McMurdo Dry Valleys select for taxa able to cope with challenging environmental conditions, including extreme chemical water activity gradients, freeze-thaw cycling, desiccation, and solar radiation regimes. The low biotic complexity of Dry Valley soils makes them well suited to investigate environmental and spatial influences on bacterial community structure. Water tracks are annually wetted habitats in the cold-arid soils of Antarctica that form briefly each summer with moisture sourced from snow melt, ground ice thaw, and atmospheric deposition via deliquescence and vapor flow into brines. Compared to neighboring arid soils, water tracks are highly saline and relatively moist habitats. They represent a considerable area (\∼5\–10 km2) of the Dry Valley terrestrial ecosystem, an area that is expected to increase with ongoing climate change. The goal of this study was to determine how variation in the environmental conditions of water tracks influences the composition and diversity of microbial communities. We found significant differences in microbial community composition between on- and off-water track samples, and across two distinct locations. Of the tested environmental variables, soil salinity was the best predictor of community composition, with members of the Bacteroidetes phylum being relatively more abundant at higher salinities and the Actinobacteria phylum showing the opposite pattern. There was also a significant, inverse relationship between salinity and bacterial diversity. Our results suggest water track formation significantly alters dry soil microbial communities, likely influencing subsequent ecosystem functioning. We highlight how Dry Valley water tracks could be a useful model system for understanding the potential habitability of transiently wetted environments found on the surface of Mars.

}, keywords = {LTER-MCM, Antarctica, extremophiles, Mars analog, microbial ecology, water tracks}, doi = {10.3389/fmicb.2021.616730}, url = {https://www.frontiersin.org/articles/10.3389/fmicb.2021.616730}, author = {George, Scott F. and Noah Fierer and Joseph S. Levy and Byron Adams} } @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 {4576, title = {Diatoms define a novel freshwater biogeography of the Antarctic}, journal = {Ecography}, volume = {44}, year = {2021}, month = {01/2021}, pages = {1-13}, abstract = {

Terrestrial biota in the Antarctic are more globally distinct and highly structured biogeographically than previously believed, but information on biogeographic patterns and endemism in freshwater communities is largely lacking. We studied biogeographic patterns of Antarctic freshwater diatoms based on the analysis of species occurrences in a dataset of 439 lakes spread across the Antarctic realm. Highly distinct diatom floras, both in terms of composition and richness, characterize Continental Antarctica, Maritime Antarctica and the sub-Antarctic islands, with marked biogeographic provincialism in each region. A total of 44\% of all species is estimated to be endemic to the Antarctic, and most of them are confined to a single biogeographic region. The level of endemism significantly increases with increasing latitude and geographic isolation. Our results have implications for conservation planning, and suggest that successful dispersal of freshwater diatoms to and within the Antarctic is limited, fostering the evolution of highly endemic diatom floras.

}, keywords = {LTER-MCM, Antarctica, biogeography, diatoms, endemism, freshwater, lake}, doi = {10.1111/ecog.05374}, url = {https://onlinelibrary.wiley.com/doi/10.1111/ecog.05374}, author = {Elie Verleyen and Bart Van de Vijver and Tytgat, Bjorn and Pinseel, Eveline and Hodgson, Dominic A. and Kopalov{\'a}, Kate{\v r}ina and Steven L. Chown and Van Ranst, Eric and Imura, Satoshi and Kudoh, Sakae and Van Nieuwenhuyze, Wim and Sabbe, Koen and Vyverman, Wim} } @article {4636, title = {Exploring the boundaries of microbial habitability in soil}, journal = {Journal of Geophysical Research: Biogeosciences}, volume = {126}, year = {2021}, month = {06/2021}, abstract = {

Microbes are widely assumed to be capable of colonizing even the most challenging terrestrial surface environments on Earth given enough time. We would not expect to find surface soils uninhabited by microbes as soils typically harbor diverse microbial communities and viable microbes have been detected in soils exposed to even the most inhospitable conditions. However, if uninhabited soils do exist, we might expect to find them in Antarctica. We analyzed 204 ice-free soils collected from across a remote valley in the Transantarctic Mountains (84\–85\°S, 174\–177\°W) and were able to identify a potential limit of microbial habitability. While most of the soils we tested contained diverse microbial communities, with fungi being particularly ubiquitous, microbes could not be detected in many of the driest, higher elevation soils\—results that were confirmed using cultivation-dependent, cultivation-independent, and metabolic assays. While we cannot confirm that this subset of soils is completely sterile and devoid of microbial life, our results suggest that microbial life is severely restricted in the coldest, driest, and saltiest Antarctic soils. Constant exposure to these conditions for thousands of years has limited microbial communities so that their presence and activity is below detectable limits using a variety of standard methods. Such soils are unlikely to be unique to the studied region with this work supporting previous hypotheses that microbial habitability is constrained by near-continuous exposure to cold, dry, and salty conditions, establishing the environmental conditions that limit microbial life in terrestrial surface soils.

}, keywords = {LTER-MCM, Antarctica, astrobiology, bacteria, extremophiles, fungi, soils}, issn = {2169-8953}, doi = {10.1029/2020JG006052}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JG006052}, author = {Dragone, Nicholas B. and Melisa A. Diaz and Hogg, Ian D. and W. Berry Lyons and W. Andrew Jackson and Diana H. Wall and Adams, Byron J. and Noah Fierer} } @mastersthesis {4588, title = {Hydrologic response to foehn winds in the McMurdo Dry Valleys, Southern Victoria Land, Antarctica}, volume = {M.S.}, year = {2021}, month = {2020}, school = {University of Colorado Boulder}, type = {masters}, address = {Boulder, CO}, abstract = {

In the McMurdo Dry Valleys (MDVs), foehn winds are a principal vector of landscape connectivity that facilitate movement of materials between glaciers, streams, soils, lakes and other parts of the ecosystem. While previous publications show that turbulent, warm and dry foehn winds indirectly relate to an increase in lake level rise via an increase in degree days above freezing (DDAF), the direct quantified impact of foehn winds to streamflow and lake level rise remains unclear. The MDVs are the largest ice-free region of Antarctica, which experience minimal precipitation. Valley bottoms contain permanently ice-covered closed basin lakes filled with meltwater from outlet glaciers via stream channels. In Taylor Valley, several meteorological stations and lake monitoring stations record average measurements of weather conditions and lake conditions on 15 to 20-minute intervals. In this thesis, the meteorological definition of foehn winds is refined and hydrologic response to foehn winds is evaluated. During the austral summer streamflow season (November - February), foehn winds are predicted to increase meltwater generation and closed-basin lake level rise. Past publications have shown that foehn wind events contribute to lake ice sublimation year-round, whereas melt does not typically occur in nonsummer months. Analysis of non-summer lake ice ablation utilizing recent lake stage and ablation data is also explored herein. Although a significant correlation was not found, summer foehn winds appear to promote above average daily lake level rise given sufficient air temperatures. Daily average lake level rise is greater for longer periods (i.e., 4-day average daily rise \> 3-day average daily rise, etc.) indicating that there is at least a 4-day post-foehn impact on lake level rise during the summer. Lake ice ablation in non-summer months is shown to have a significant relationship with increasing foehn wind occurrence and wind-run. Because foehn winds are expected to increase with global warming, these hydrologic relationships aid in predicting the future of the McMurdo Dry Valley ecosystem in a warming world.

}, keywords = {LTER-MCM, Antarctica, foehn, foehn winds, hydrologic, katabatic, McMurdo, wind}, url = {https://www.proquest.com/docview/2488126937}, author = {Beane, Samuel J. and Michael N. Gooseff} } @book {4946, title = {The McMurdo Dry Valleys of Antarctica: A geological, environmental, and ecological analog to the Martian surface and near surface}, year = {2021}, publisher = {Elsevier}, organization = {Elsevier}, abstract = {

The surface of Mars is universally thought to have experienced widespread cold and dry environmental conditions for at least the last half of its geologic history, with more modern studies suggesting relatively cold and dry conditions early in its geologic history as well. However, the paucity of liquid water and mean annual temperatures well below the freezing point of water do not necessarily mean a complete cessation of all water-related geologic activity at the Martian surface. Over the past several decades, investigations in the McMurdo Dry Valleys (MDV) of Antarctica have revealed a dynamic geological, environmental, and ecological system resulting from locally optimized conditions operating over repeated, albeit brief, intervals during summer months. In this chapter, we compare the hyper-arid and hypo-thermal environments of the MDV and the modern Martian surface and discuss three unique enigmas that demonstrate how the Antarctic is a valuable analog to better understand processes on Mars.

}, keywords = {LTER-MCM, Antarctica, astrobiology, climate, geology, geomorphology, Mars}, isbn = {9780128202456}, doi = {10.1016/B978-0-12-820245-6.00011-2}, url = {https://www.sciencedirect.com/science/article/pii/B9780128202456000112}, author = {Salvatore, Mark R. and Joseph S. Levy} } @article {4645, title = {Phagotrophic protists and their associates: Evidence for preferential grazing in an abiotically driven soil ecosystem}, journal = {Microorganisms}, volume = {9}, year = {2021}, month = {08/2021}, pages = {1555}, abstract = {

The complex relationship between ecosystem function and soil food web structure is governed by species interactions, many of which remain unmapped. Phagotrophic protists structure soil food webs by grazing the microbiome, yet their involvement in intraguild competition, susceptibility to predator diversity, and grazing preferences are only vaguely known. These species-dependent interactions are contextualized by adjacent biotic and abiotic processes, and thus obfuscated by typically high soil biodiversity. Such questions may be investigated in the McMurdo Dry Valleys (MDV) of Antarctica because the physical environment strongly filters biodiversity and simplifies the influence of abiotic factors. To detect the potential interactions in the MDV, we analyzed the co-occurrence among shotgun metagenome sequences for associations suggestive of intraguild competition, predation, and preferential grazing. In order to control for confounding abiotic drivers, we tested co-occurrence patterns against various climatic and edaphic factors. Non-random co-occurrence between phagotrophic protists and other soil fauna was biotically driven, but we found no support for competition or predation. However, protists predominately associated with Proteobacteria and avoided Actinobacteria, suggesting grazing preferences were modulated by bacterial cell-wall structure and growth rate. Our study provides a critical starting-point for mapping protist interactions in native soils and highlights key trends for future targeted molecular and culture-based approaches.

}, keywords = {LTER-MCM, Antarctica, co-occurrence networks, McMurdo Dry Valleys, Rhogostoma sp., Sandona sp., soil food webs, variation partitioning}, doi = {10.3390/microorganisms9081555}, url = {https://www.mdpi.com/2076-2607/9/8/1555}, author = {Thompson, Andrew R. and Roth-Monz{\'o}n, Andrea J. and Aanderud, Zachary T. and Adams, Byron J.} } @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} } @phdthesis {4692, title = {Stream corridor connectivity controls on nitrogen cycling}, volume = {PhD}, year = {2021}, month = {05/2021}, school = {University of Colorado Boulder}, type = {Doctoral}, address = {Boulder, CO, USA}, abstract = {

As water flows downstream, it is transported to and from environments that surround the visible stream. Along with surface water, these laterally and vertically connected environments comprise the stream corridor. Stream corridor connectivity influences many ecosystem services, including retention of excess nutrients. The subsurface area where stream water and groundwater mixes\—the hyporheic zone\—represents one of the most biogeochemically active parts of stream corridors.

The goal of my research is to advance understanding of how connectivity between different parts of a stream corridor controls the availability and retention of nitrogen (N), a nutrient that can limit primary productivity (low-N) and negatively impact water quality (excess N). First, I developed and applied a new machine learning method to objectively characterize the extent and variability of hyporheic exchange in terms of statistically unique functional zones using geophysical data. In applying this method to a benchmark dataset, I found that hyporheic extent does not scale uniformly with streamflow and that changes in the heterogeneity of connectivity differ over small (\<10 m) distances. Next, I leveraged the relative simplicity of ephemeral streams of the McMurdo Dry Valleys (MDVs), Antarctica, to isolate stream corridor processes that influence the fate of N. Through intensive field sampling campaigns, I found that the hyporheic zone can be a persistent source of N even in this low nutrient environment. Next, I combined historic sample data and remote sensing analysis to estimate how much N is stored in an MDV stream corridor. My results indicate that up to 103 times more N is stored in this system than is exported each year, with most of this storage in the shallow (\< 10 cm) hyporheic zone. Lastly, I examined 25 years of data for 10 streams to assess how stream corridor processes control concentration-discharge relationships. I found that in the absence of hillslope connectivity, stream corridor processes alone can maintain chemostasis \– relatively small concentration changes with large fluctuations in streamflow \– of both geogenic solutes and primary nutrients. My analysis also revealed that solutes subject to greater control by biological processes exhibit more variability within chemostatic relationships than weathering solutes that are only minimally influenced by biota.

Altogether, this research advances understanding of processes that are difficult to measure or are often overlooked in typical studies of temperate stream corridors. My findings provide insight into the surprising ways in which N is mobilized, transformed, and retained due to stream corridor connectivity in intermittent stream systems with few N inputs.

}, keywords = {LTER-MCM, Antarctica, hyporheic zone, nitrogen cycling, streams}, url = {https://www.proquest.com/docview/2572593127}, author = {Singley, Joel G.}, editor = {Eve-Lyn S. Hinckley and Michael N. Gooseff} } @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} } @thesis {4443, title = {Analysis of acid-leachable barium, copper, iron, lead, \& zinc concentrations in Taylor Valley, Antarctic stream sediments}, volume = {B.S.}, year = {2020}, month = {05/2020}, school = {The Ohio State University}, type = {bachelors}, address = {Columbus, OH}, abstract = {

The purpose of this study is to assess the concentrations of Barium (Ba), Copper (Cu), Iron (Fe), Lead (Pb), and Zinc (Zn) in sediment samples obtained from the Wales and Commonwealth streams located in Taylor Valley, Antarctica. These samples were collected at seven sample sites (three in Wales Glacier and four in Commonwealth Glacier) in 0 to 2 cm, 2 to 4 cm, 4 to 6 cm, and 6 to 8 cm depth increments which resulted in 28 total samples. After the collection process, these samples underwent a volumetric 1:5 sediment: 10\% HCl leach for 48 hours, filtration through 4-\µm pore-size, cellulose acetate membrane filters, and inductively coupled plasma mass spectrometry (ICP-MS) analyses in the Trace Element Research Laboratory at The Ohio State University. Upon completion of the analyses, results showed that the Wales samples had a higher average concentration of every metal element overall and at each depth increment when compared to the Commonwealth samples. In addition to the weak-acid leachate metal analyses, a second aliquot of one sediment profile from each stream was analyzed at Villanova University for the 210Pb activity via gamma spectroscopy. This was done to estimate the sedimentation rates at each of these sites. From the sedimentation rates, sedimentation fluxes were calculated for each element for each sediment profile at each of these sites. The data demonstrated that Fe is the most abundant element while Pb is the least abundant. Lastly, upon examination of results, it was found that the concentrations of these metals are often higher in samples collected closer to the surface. These findings suggest these streams, and their sources, have had little, if any, impact by anthropogenic input of metals, and that metal fluxes to the sediments are low.

}, keywords = {LTER-MCM, acid-leachable metal, Antarctica, geochemistry, McMurdo Dry Valleys, polar sediments, sedimentation rate}, url = {http://hdl.handle.net/1811/91772}, author = {Piergallini, Brianna and W. Berry Lyons} } @article {4395, title = {Energetic and environmental constraints on the community structure of benthic microbial mats in Lake Fryxell, Antarctica}, journal = {FEMS Microbiology Ecology}, volume = {96}, year = {2020}, month = {02/2020}, abstract = {

Ecological communities are regulated by the flow of energy through environments. Energy flow is typically limited by access to photosynthetically active radiation (PAR) and oxygen concentration (O2). The microbial mats growing on the bottom of Lake Fryxell, Antarctica, have well-defined environmental gradients in PAR and (O2). We analyzed the metagenomes of layers from these microbial mats to test the extent to which access to oxygen and light controls community structure. We found variation in the diversity and relative abundances of Archaea, Bacteria and Eukaryotes across three (O2) and PAR conditions: high (O2) and maximum PAR, variable (O2) with lower maximum PAR, and low (O2) and maximum PAR. We found distinct communities structured by the optimization of energy use on a millimeter-scale across these conditions. In mat layers where (O2) was saturated, PAR structured the community. In contrast, (O2) positively correlated with diversity and affected the distribution of dominant populations across the three habitats, suggesting that meter-scale diversity is structured by energy availability. Microbial communities changed across covarying gradients of PAR and (O2). The comprehensive metagenomic analysis suggests that the benthic microbial communities in Lake Fryxell are structured by energy flow across both meter- and millimeter-scales.

}, keywords = {LTER-MCM, Antarctica, energy, Lake Fryxell, microbial mat, Oxygen, Photosynthetically Active Radiation}, doi = {10.1093/femsec/fiz207}, url = {https://academic.oup.com/femsec/article/96/2/fiz207/5697196}, author = {Dillon, Megan L. and Ian Hawes and Jungblut, Anne D. and Mackey, Tyler J. and Eisen, Jonathan A. and Peter T. Doran and Sumner, Dawn Y.} } @article {4516, title = {Estimating microbial mat biomass in the McMurdo Dry Valleys, Antarctica using satellite imagery and ground surveys}, journal = {Polar Biology}, year = {2020}, month = {09/2020}, abstract = {

Cyanobacterial mat communities are the main drivers of primary productivity in the McMurdo Dry Valleys, Antarctica. These microbial communities form laminar mats on desert pavement surfaces adjacent to glacial meltwater streams, ponds, and lakes. The low-density nature of these communities and their patchy distribution make assessments of distribution, biomass, and productivity challenging. We used satellite imagery coupled with in situ surveying, imaging, and sampling to systematically estimate microbial mat biomass in selected wetland regions in Taylor Valley, Antarctica. On January 19th, 2018, the WorldView-2 multispectral satellite acquired an image of our study areas, where we surveyed and sampled seven 100 m2 plots of microbial mats for percent ground cover, ash-free dry mass (AFDM), and pigment content (chlorophyll-a, carotenoids, and scytonemin). Multispectral analyses revealed spectral signatures consistent with photosynthetic activity (relatively strong reflection at near-infrared wavelengths and relatively strong absorption at visible wavelengths), with average normalized difference vegetation index (NDVI) values of 0.09 to 0.28. Strong correlations of microbial mat ground cover (R2\ =\ 0.84), biomass (R2\ =\ 0.74), chlorophyll-a content (R2\ =\ 0.65), and scytonemin content (R2\ =\ 0.98) with logit transformed NDVI values demonstrate that satellite imagery can detect both the presence of microbial mats and their key biological properties. Using the NDVI\—biomass correlation we developed, we estimate carbon (C) stocks of 21,715 kg (14.7 g C m\−2) in the Canada Glacier Antarctic Specially Protected Area, with an upper and lower limit of 74,871 and 6312 kg of C, respectively.

}, keywords = {LTER-MCM, Antarctica, microbial mat, multispectral imagery, NDVI, Nostocales, remote sensing}, doi = {10.1007/s00300-020-02742-y}, url = {https://link.springer.com/article/10.1007\%2Fs00300-020-02742-y}, author = {Power, Sarah N. and Salvatore, Mark R. and Eric R. Sokol and Lee F. Stanish and John E. Barrett} } @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 {4487, title = {Glycerol is an osmoprotectant in two Antarctic Chlamydomonas species from an ice-covered saline lake and is synthesized by an unusual bidomain enzyme}, journal = {Frontiers in Plant Science}, volume = {11}, year = {2020}, month = {08/2020}, abstract = {

Glycerol, a compatible solute, has previously been found to act as an osmoprotectant in some marine Chlamydomonas species and several species of Dunaliella from hypersaline ponds. Recently, Chlamydomonas reinhardtii and Dunaliella salina were shown to make glycerol with an unusual bidomain enzyme, which appears to be unique to algae, that contains a phosphoserine phosphatase and glycerol-3-phosphate dehydrogenase. Here we report that two psychrophilic species of Chlamydomonas (C. spp. UWO241 and ICE-MDV) from Lake Bonney, Antarctica also produce high levels of glycerol to survive in the lake\’s saline waters. Glycerol concentration increased linearly with salinity and at 1.3 M NaCl, exceeded 400 mM in C. sp. UWO241, the more salt-tolerant strain. We also show that both species expressed several isoforms of the bidomain enzyme. An analysis of one of the isoforms of C. sp. UWO241 showed that it was strongly upregulated by NaCl and is thus the likely source of glycerol. These results reveal another adaptation of the Lake Bonney Chlamydomonas species that allow them to survive in an extreme polar environment.

}, keywords = {LTER-MCM, Antarctica, Chlamydomonas, glycerol synthesis, glycerol-3-phosphate dehydrogenase, Lake Bonney, phosphoserine phosphatase}, doi = {10.3389/fpls.2020.01259}, url = {https://www.frontiersin.org/articles/10.3389/fpls.2020.01259/full}, author = {Raymond, James A. and Rachael M. Morgan-Kiss and Stahl-Rommel, Sarah} } @article {4439, title = {The rise of technocratic environmentalism: the United States, Antarctica, and the globalisation of the environmental impact statement}, journal = {Journal of Historical Geography}, year = {2020}, month = {05/2020}, abstract = {

Environmental impact statements (EISs), and the related environmental impact assessments (EIAs) which precede them, have become central elements of environmental management, governance, and policy worldwide since their introduction in the United States in 1970. Assessing environmental impact has a particular force and centrality within modern Antarctic environmental management and governance too. This article investigates the ways in which the United States used EISs and EIAs in Antarctica between 1970 and 1982 \– during their first decade of existence in US law and during a geopolitically and scientifically vibrant decade in Antarctic affairs \– as a way of illuminating the broader conceptual and historical aspects of this central, though understudied, environmental governance tool and framework. We historicise and draw attention to the EIS \– individually, as a regulatory genre, and as a genre that articulates regional, global and planetary environments \– as highly influential and powerful documents demanding attention from environmental historians and historical geographers. We argue that the prominence of EISs in Antarctica arose because they appealed to top-down, process-oriented approaches favoured in Antarctic governance \– a technocratic environmentalism \– and because of their spatial elements, particularly their tendency to upscaling.

}, keywords = {LTER-MCM, Antarctica, Conservation, Environmental impact statements, Environmental protection, National Environmental Policy Act (NEPA)}, doi = {10.1016/j.jhg.2020.03.004}, url = {https://www.sciencedirect.com/science/article/abs/pii/S030574882030027X}, author = {Antonello, Alessandro and Howkins, Adrian} } @article {4490, title = {Shotgun metagenomics reveal a diverse assemblage of protists in a model Antarctic soil ecosystem}, journal = {Environmental Microbiology}, year = {2020}, month = {08/2020}, abstract = {

The soils of the McMurdo Dry Valleys (MDV) of Antarctica are established models for understanding fundamental processes in soil ecosystem functioning (e.g. ecological tipping points, community structuring, and nutrient cycling) because the extreme physical environment drastically reduces biodiversity and ecological complexity. Understanding the functioning of MDV soils requires in-depth knowledge of the diversity of MDV soil species. Protists, which contribute significantly to soil ecosystem functioning worldwide, remain poorly characterized in the MDV. To better assess the diversity of MDV protists, we performed shotgun metagenomics on 18 sites representing a variety of landscape features and edaphic variables. Our results show MDV soil protists are diverse at both the genus (155 of 281 eukaryote genera) and family (120) levels, but comprise only 6\% of eukaryotic reads. Protists are structured by moisture, total N, and distance from the local coast, and possess limited richness in arid (\<5\% moisture) and at high elevation sites, known drivers of communities in the MDV. High relative diversity and broad distribution of protists in our study promotes these organisms as key members of MDV soil microbiomes and the MDV as a useful system for understanding the contribution of soil protists to the structure of soil microbiomes.

}, keywords = {LTER-MCM, Antarctica, extremophiles, functional groups, metagenomics, protozoa, soil microbiology}, doi = {10.1111/1462-2920.15198}, url = {https://sfamjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1462-2920.15198}, author = {Thompson, Andrew R. and Geisen, Stefan and Byron Adams} } @article {4154, title = {The Antarctic psychrophiles Chlamydomonas spp. UWO241 and ICE-MDV exhibit differential restructuring of photosystem I in response to iron}, journal = {Photosynthesis Research}, volume = {9}, year = {2019}, month = {02/2019}, abstract = {

Chlamydomonas sp. UWO241 is a psychrophilic alga isolated from the deep photic zone of a perennially ice-covered Antarctic lake (east lobe Lake Bonney, ELB). Past studies have shown that C. sp. UWO241 exhibits constitutive downregulation of photosystem I (PSI) and high rates of PSI-associated cyclic electron flow (CEF). Iron levels in ELB are in the nanomolar range leading us to hypothesize that the unusual PSI phenotype of C. sp. UWO241 could be a response to chronic Fe-deficiency. We studied the impact of Fe availability in C. sp. UWO241, a mesophile, C. reinhardtii SAG11-32c, as well as a psychrophile isolated from the shallow photic zone of ELB, Chlamydomonas sp. ICE-MDV. Under Fe-deficiency, PsaA abundance and levels of photooxidizable P700 (ΔA820/A820) were reduced in both psychrophiles relative to the mesophile. Upon increasing Fe, C. sp. ICE-MDV and C. reinhardtii exhibited restoration of PSI function, while C. sp. UWO241 exhibited only moderate changes in PSI activity and lacked almost all LHCI proteins. Relative to Fe-excess conditions (200 μM Fe2+), C. sp. UWO241 grown in 18 μM Fe2+ exhibited downregulation of light harvesting and photosystem core proteins, as well as upregulation of a bestrophin-like anion channel protein and two CEF-associated proteins (NdsS, PGL1). Key enzymes of starch synthesis and shikimate biosynthesis were also upregulated. We conclude that in response to variable Fe availability, the psychrophile C. sp. UWO241 exhibits physiological plasticity which includes restructuring of the photo-chemical apparatus, increased PSI-associated CEF, and shifts in downstream carbon metabolism toward storage carbon and secondary stress metabolites.

}, keywords = {LTER-MCM, Antarctica, Cyclic electron flow, Iron, Photosystem I, Psychrophile}, issn = {0166-8595}, doi = {10.1007/s11120-019-00621-0}, url = {https://link.springer.com/article/10.1007/s11120-019-00621-0}, author = {Cook, Greg and Teufel, Amber and Kalra, Isha and Li, Wei and Wang, Xin and John C. Priscu and Rachael M. Morgan-Kiss} } @article {4188, title = {The geochemistry of glacial deposits in Taylor Valley, Antarctica: Comparison to upper continental crustal abundances}, journal = {Applied Geochemistry}, year = {2019}, month = {05/2019}, abstract = {

Wet-based glacial deposits have been used traditionally as an analog for upper continental crust (UCC) abundances. To provide more information on the validity of using glacial deposits from wet-based glaciers, samples deposited by the dry-based polar glaciers located in Taylor Valley, Antarctica, were collected. Stream channel sediments, comprised of igneous, metamorphic, and sedimentary rocks initially deposited as glacial tills by polar glaciers, were analyzed by XRF, ICP-MS, and SEM. Based on the Chemical Index of Alteration values and A\–CN\–K ternary diagram, there are low levels of chemical weathering in these tills. Additionally, major and trace element geochemical data are compared to the average UCC values. The observed discrepancies between the mean UCC and Antarctic samples develop from the existence of mafic components, most likely the McMurdo Volcanic Group and Ferrar Dolerite, being present in the Taylor Valley tills. Even though the mafic material typically comprises 3\–7\% of the till, the volcanic rocks have a significant influence on the tills\’ bulk geochemistry. The existence of this mafic fraction in the dry-based glacial tills results from the reduced rate of weathering, as compared to wet-based glaciers. Geochemical analyses of the dry-based glacial tills in polar deserts, such as those found in Taylor Valley, may provide a better representative composition of the original material than wet-based glaciers and need to be incorporated into upper continental crust calculations.

}, keywords = {LTER-MCM, Antarctica, geochemistry, glacial deposits, polar dry-based glaciers, Taylor Valley}, doi = {10.1016/j.apgeochem.2019.05.006}, url = {https://www.sciencedirect.com/science/article/pii/S0883292719301246}, author = {Carolyn Dowling and Sue Welch and W. Berry Lyons} } @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 {4837, title = {Meteorological connectivity from regions of high biodiversity within the McMurdo Dry Valleys of Antarctica}, journal = {Journal of Applied Meteorology and Climatology}, volume = {58}, year = {2019}, month = {11/2019}, pages = {2437 - 2452}, abstract = {

Meteorological connectivity between biological hot spots of the McMurdo Dry Valleys (MDVs) of Antarctica is thought to play a role in species distribution and abundance through the aeolian transport of bioaerosols. Understanding the potential role of such meteorological connectivity requires an understanding of near-surface wind flow within and between valley airsheds. To address this, we applied Lagrangian wind trajectory modeling to mesoscale (spatial resolution of ~1 km) weather model output to predict connectivity pathways, focusing on regions of high biodiversity. Our models produce maps of a likelihood metric of wind connectivity that demonstrate the synoptic and mesoscale dependence of connections between local, near-local, and nonlocal areas on wind transport, modulated by synoptic weather and topographic forcing. These connectivity areas can have spatial trends modulated by the synoptic weather patterns and locally induced topographically forced winds. This method is transferrable to other regions of Antarctica for broader terrestrial, coastal, and offshore ecological connectivity research. Also, our analysis and methods can inform better placement of aeolian dust and bioaerosol samplers in the McMurdo Dry Valleys, provide preliminary guidelines behind the meteorological controls of sediment transport and smaller particle distribution, and present quantifiable knowledge informing new hypotheses around the potential of wind acting as a physical driver for biological connectivity in the MDVs.

}, keywords = {LTER-MCM, Antarctica, atmosphere, biosphere-atmosphere interaction, mesoscale models, mesoscale processes, numerical analysis/modeling}, issn = {1558-8424}, doi = {10.1175/JAMC-D-18-0336.1}, url = {https://journals.ametsoc.org/view/journals/apme/58/11/jamc-d-18-0336.1.xml}, author = {Katurji, Marwan and Khan, Basit and Sprenger, Michael A. and Datta, Rajasweta and Joy, Kurt and Zawar-Reza, Peyman and Ian Hawes} } @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 {4105, title = {Dissolved Trace and Minor Elements in Cryoconite Holes and Supraglacial Streams, Canada Glacier, Antarctica}, journal = {Frontiers in Earth Science}, volume = {6}, year = {2018}, month = {04/2018}, abstract = {

We present a synthesis of the trace element chemistry in melt on the surface Canada Glacier, Taylor Valley, McMurdo Dry Valleys (MDV), Antarctica (\∼78{\textopenbullet}S). The MDV is largely ice-free. Low accumulation rates, strong winds, and proximity to the valley floor make these glaciers dusty in comparison to their inland counterparts. This study examines both supraglacial melt streams and cryoconite holes. Supraglacial streams on the lower Canada Glacier have median dissolved (\<0.4\ μm) concentrations of Fe, Mn, As, Cu, and V of 71.5, 75.5, 3.7, 4.6, and 4.3 nM. All dissolved Cd concentrations and the vast majority of Pb values are below our analytical detection (i.e., 0.4 and 0.06 nM). Chemical behavior did not follow similar trends for eastern and western draining waters. Heterogeneity likely reflects distinctions eolian deposition, rock:water ratios, and hydrologic connectivity. Future increases in wind-delivered sediment will likely drive dynamic responses in melt chemistry. For elements above detection limits, dissolved concentrations in glacier surface melt are within an order of magnitude of concentrations observed in proglacial streams (i.e., flowing on the valley floor). The Fe enrichment of cryoconite water relative to N, P, or Si exceeds enrichment observed in marine phytoplankton. This suggests that the glacier surface is an important source of Fe to downstream ecosystems.

}, keywords = {LTER-MCM, Antarctica, cryoconite holes, glacier melt chemistry, supraglacial streams, trace elements}, doi = {10.3389/feart.2018.00031}, url = {http://journal.frontiersin.org/article/10.3389/feart.2018.00031/full}, author = {Sarah Fortner and W. Berry Lyons} } @article {4155, title = {Photoecology of the Antarctic cyanobacterium Leptolyngbya sp. BC1307 brought to light through community analysis, comparative genomics and in vitro photophysiology}, journal = {Molecular Ecology}, volume = {27}, year = {2018}, month = {11/2018}, pages = {5279 - 5293}, abstract = {

Cyanobacteria are important photoautotrophs in extreme environments such as the McMurdo Dry Valleys, Antarctica. Terrestrial Antarctic cyanobacteria experience constant darkness during the winter and constant light during the summer which influences the ability of these organisms to fix carbon over the course of an annual cycle. Here, we present a unique approach combining community structure, genomic and photophysiological analyses to understand adaptation to Antarctic light regimes in the cyanobacterium Leptolyngbya sp. BC1307. We show that Leptolyngbya sp. BC1307 belongs to a clade of cyanobacteria that inhabits near-surface environments in the McMurdo Dry Valleys. Genomic analyses reveal that, unlike close relatives, Leptolyngbya sp. BC1307 lacks the genes necessary for production of the pigment phycoerythrin and is incapable of complimentary chromatic acclimation, while containing several genes responsible for known photoprotective pigments. Photophysiology experiments confirmed Leptolyngbya sp. BC1307 to be tolerant of short-term exposure to high levels of photosynthetically active radiation, while sustained exposure reduced its capacity for photoprotection. As such, Leptolyngbya sp. BC1307 likely exploits low-light microenvironments within cyanobacterial mats in the McMurdo Dry Valleys.

}, keywords = {LTER-MCM, Antarctica, cyanobacteria, genomics, photoecology, photophysiology}, doi = {10.1111/mec.14953}, url = {https://onlinelibrary.wiley.com/doi/full/10.1111/mec.14953}, author = {Chrismas, Nathan A. M. and Williamson, Christopher J. and Yallop, Marian L. and Alexandre M. Anesio and S{\'a}nchez-Baracaldo, Patricia} } @article {4020, title = {Glaciers in equilibrium, McMurdo Dry Valleys, Antarctica}, journal = {Journal of Glaciology}, volume = {62}, year = {2016}, month = {07/2016}, pages = {976 - 989}, abstract = {

The McMurdo Dry Valleys are a cold, dry polar desert and the alpine glaciers therein exhibit small annual and seasonal mass balances, often \<\±0.06 m w.e. Typically, winter is the accumulation season, but significant snow storms can occur any time of year occasionally making summer the accumulation season. The yearly equilibrium line altitude is poorly correlated with mass balance because the elevation gradient of mass balance on each glacier can change dramatically from year to year. Most likely, winds redistribute the light snowfall disrupting the normal gradient of increasing mass balance with elevation. Reconstructed cumulative mass balance shows that the glaciers have lost \<2 m w.e. over the past half century and area changes show minimal retreat. In most cases these changes are less than the uncertainty and the glaciers are considered in equilibrium. Since 2000, however, the glaciers have lost mass despite relatively stable summer air temperatures suggesting a different mechanism in play. Whether this trend is a harbinger of future changes or a temporary excursion is unclear.

}, keywords = {LTER-MCM, Antarctica, glaciers, mass balance}, issn = {0022-1430}, doi = {10.1017/jog.2016.86}, url = {https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143016000861}, author = {Andrew G Fountain and Hassan J. Basagic and Niebuhr, Spencer} } @phdthesis {4167, title = {Influence of abiotic drivers (light and nutrients) on photobiology and diversity of Antarctic lake phytoplankton communities}, volume = {Ph.D.}, year = {2016}, month = {2016}, school = {Miami University}, type = {doctoral}, address = {Oxford, OH}, abstract = {

Arctic, Antarctic, and alpine ecosystems are recognized as sensors and sentinels of global climate change. As a consequence of their high sensitivity to minor climatic perturbations, permanently ice-covered lakes located in the McMurdo Dry Valleys (MCM), Antarctica, represent end members in the global network of inland bodies of water. Episodic climatic events in the form of increased summer glacial melt result in inputs of organic sediment and nutrients from glacial streams to these closed basins. By better understanding how Antarctic lake communities respond to mimicked climate change, we can more accurately predict how they will react to further temperature changes in the future. We began by investigating the influence of inorganic nitrogen and phosphorus availability on planktonic communities residing in the oligotrophic upper waters of two chemically distinct MCM lakes (Lakes Bonney and Fryxell) which differ in their external inputs as well as water column N:P stoichiometry. Although microbial community responses varied between the lakes and were nutrient-dependent, stimulation of phytoplankton biomass and productivity across all treatments was strongly linked with increased abundance of a single phytoplankton phylum (Chlorophyta). Despite stimulation of phytoplankton growth, primary and bacterial productivity were largely uncoupled across all enrichments. We suggest that climate-associated shifts in phytoplankton diversity influence the bacterial community structure by altering the availability and composition of autochthonous carbon for heterotrophic production. To monitor the physiological adaptations that occur over time and depth, we then transplanted two dominant phytoplankton, Chlamydomonas sp. ICE- MDV and Isochrysis sp. MDV back into the Lake Bonney water column. Our results demonstrated that both organisms are specialists for surviving specific depths of the water column and are capable of acclimating to their native environment within a short period of time, and that the chlorophyte Chlamydomonas sp. ICE-MDV most likely makes this adjustment via photoacclimation and accumulating chlorophyll-a per cell. The final study presented here investigated whether or not the dominant chlorophyte, Chlamydomonas sp. ICE-MDV has retained the ability to respond to a diel 12-hour day/night cycle. Although light levels in MCM lakes remain low during the austral summers, daily irradiation varies by as much as tenfold during the course of the day, resulting in a circadian-like light cycle for organisms residing there. With decreased ice coverage on the lakes due to climate change and increased melt, it is likely that these light variations will become amplified over time. This study tested for the presence of a circadian rhythm under various light quality, light quantity, and temperature conditions and demonstrated that although a diel rhythm was maintained in terms of growth and several photochemical parameters, a true circadian rhythm was not identified. Although it is predicted that photosynthetic communities in polar regions will be more responsive to climate warming and episodic events, the complexity of these systems provides numerous challenges to understanding how these organism will adapt in the future.

}, keywords = {LTER-MCM, Antarctica, bacterial production, Chlamydomonas sp ICE MDV, Chlorophyll fluorescence, circadian rhythm, climate change, McMurdo Dry Valleys, nutrient amendment, photobiology, Primary production}, url = {http://rave.ohiolink.edu/etdc/view?acc_num=miami1468411564}, author = {Teufel, Amber G. and Rachael M. Morgan-Kiss} } @mastersthesis {4096, title = {Noble Gas Radioisotope Constraints on Water Residence Time and Solvent Sources in Lake Bonney}, volume = {M.S.}, year = {2016}, school = {University of Illinois}, type = {masters}, address = {Chicago, IL}, abstract = {

A noble gas radionuclide analysis of perennially ice covered West Lake Bonney was performed in order to determine water residence time and ice cover timing. Bulk gas samples were collected at four depths in the lake. Krypton and argon gases were selectively isolated from the bulk gas and measurements of 81Kr, 85Kr and 39Ar were made. Radiokrypton and radioargon analyses yielded lower limit ages of 78 to 285 years, significantly younger than expected based on previous dating efforts. It was determined that these new data do not invalidate previous work, but instead offer new insight into the timing of the most recent episode of direct communication between the atmosphere and West Lake Bonney waters.

}, keywords = {LTER-MCM, Antarctica, noble gas, radioargon, radiokrypton, residence time}, url = {http://hdl.handle.net/10027/21570}, author = {Cronin, Kyle D. and Peter T. Doran} } @mastersthesis {4192, title = {The impacts of thermokarst activity on a stream in the McMurdo Dry Valleys}, volume = {M.S.}, year = {2015}, month = {2015}, pages = {70}, school = {University of Colorado}, type = {masters}, address = {Boulder, CO}, abstract = {

The McMurdo Dry Valleys (MDV) of Antarctica are a unique ice-free landscape that is host to vibrant ecosystems despite the harsh environment (\<10 cm water equivalent/yr, -20\°C mean air temperature). Aquatic ecosystems in the MDV are dependent on the ephemeral glacial runoff streams which feed the closed basin perennially ice covered lakes. The upland zones of the Dry Valleys have been shown to have some of the slowest ground surface change rates in the world. However, recent observations in the coastal valley transition zones suggest that this area may be nearing a threshold of rapid landscape change.

One of the recent observations that supports this idea is the discovery of extensive thermokarst degradation (permafrost thaw features) along the banks of Crescent Stream in Taylor Valley. In 2012, a large stretch of the West Branch of Crescent Stream was found to have significant thermokarst bank failures, while the adjacent East Branch was found to be unaffected. The thermokarst impacts within this setting are important to understand because of the disturbances that massive sediment loading can impose on downstream biological communities.

Annually repeated terrestrial LiDAR scans (3) were compared to determine the rates of ground surface change due to thermokarst degradation. It was found that the areal extent of the thermokarst was decreasing, however the average linear rates of retreat remained constant. Field measurements including, pebble counts, fine sediment counts, and sieve samples were analyzed to determine the effects of the thermokarst on the stream bed material. It was found that the West Branch and the reach downstream of the confluence were consistently finer than the unaffected East Branch. This suggests that the finer bed material is due to the thermokarst bank degradation. Stream power was calculated for multiple reaches to be used as a metric for the mobilization of the streambed material. It was found that both branches infrequently experience flows substantial enough to mobilize the bed material. Even the finer bed material of the impacted West Branch reach required flows that had a 5 \% chance of exceedance for mobilization of the bed. These findings suggest the West Branch of Crescent Stream and the biota supported by this branch of the stream, continue to adjust to the sediment introduced from the thermokarst bank degradation.

}, keywords = {LTER-MCM, Antarctica, Dry valleys, earth sciences, stream, thermokarst}, url = {https://search.proquest.com/docview/1717582573}, author = {Sudman, Zachary and Michael N. Gooseff} } @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} } @phdthesis {4097, title = {Geophysics, Water Balance, and History of Thick Perennial Ice Covers on Antarctic Lakes}, volume = {Ph.D.}, year = {2014}, school = {University of Illinois}, type = {doctoral}, address = {Chicago, IL}, abstract = {

Antarctic lakes are studied as sentinels of future change, for paleolimnological records contained in the sediments, and as habitats for the simple food webs that can exist in inhospitable environments. Understanding how lakes are formed and are sustained in response to landscape and climate conditions is critical in addressing the aforementioned research themes. This thesis is governed by the overarching hypothesis that an understanding of hydrologic and sediment transport processes associated with lake ice formation and preservation can be used to reveal past climatic changes, and further our awareness of current changes in climate and water balance in the McMurdo Dry Valleys of Antarctica. The first chapter focuses on water loss from closed basin lakes in Taylor Valley, Antarctica, and presents updated estimates of sublimation and ablation rates from long-term empirical measurements. The second and third chapters address the formation of Lake Vida, Antarctica. The former investigates the accretion of a 27 m ice cover, and considers the origin of thick sediment layers in the ice cover, and the latter uses two geophysical methods to quantify the extent and volume of the brine network in the subsurface beneath the lake. The results presented herein advance the study of hydrogeology in continuous permafrost, provide additional evidence for fluctuating climate states in the McMurdo Dry Valleys throughout the mid to late Holocene, and provide a case study for the preservation of water in a cold, desert environment analogous to neighboring planets.

}, keywords = {LTER-MCM, Antarctica, brine, lake ice, McMurdo Dry Valleys, polar lakes, sublimation}, url = {http://hdl.handle.net/10027/19407}, author = {Hilary A. Dugan}, editor = {Peter T. Doran} } @phdthesis {4367, title = {The application of stable isotopes, δ11B, δ18O, and δD, in geochemical and hydrological investigations}, volume = {Ph.D.}, year = {2013}, school = {Ohio State University}, type = {doctoral}, address = {Columbus, OH}, abstract = {

My dissertation research utilizes stable isotopes as tracers of water and solute sources to study specific geochemical (solute origin) and hydrological (glacier meltwater source across a season comparing water contributions from hyporheic zone and/or glacier melt and residence time of precipitation within a managed water supply) problems within McMurdo Dry Valleys (MCM), Antarctica, and Central Ohio, USA. In Chapter II, δ11B isotopic and dissolved B measurements are used to infer the origin of B within MCM aquatic system. Boron stable isotopic values span the range of +12.3\‰ to +51.4\‰, varying from glacier meltwater streams to the hypolimnion of a highly evaporated hypersaline lake. These data demonstrate that the major sources of B are chemical weathering of alumniosilicates within the stream channels, and a marine source, either currently introduced by marine-derived aerosols or from ancient seawater. In-lake processes create a more positive δ11B through adsorption or mineral precipitation. The glacier meltwater streams, Lakes Fryxell, Hoare, and upper waters of Lake Joyce display a mixture of these two sources, with Lake Joyce bottom waters primarily of marine origin. Lakes Bonney and Vanda and Blood Falls brine are interpreted as having a marine-like source changed by in-lake processes to result in a more positive δ11B, while Don Juan Pond displays a more terrestrial influence. In Chapter III, δ18O and δD are used to trace water source variation via hyporheic zone or glacier melt within two MCM streams over an entire melt season. The isotopic variation of these streams was more negative at the beginning of the season and more positive later. D-excess measurements were used to infer mixing between hyporheic storage and glacier meltwater. It was supported that Von Guerard Stream has a large, widespread hyporheic zone that changes with time and discharge amounts. The chemistry of Andersen Creek also displayed hyporheic zone influence at certain times of the year. This work adds important new information on the role of hyperheic zone-stream interactions, and supports the short term, more physically based, descriptions of hyporheic dynamics explained in the past decade. Chapter IV describes water flow and travel time within a human managed watershed-reservoir system by measuring the δ18O and δD of the precipitation source to the reservoirs and finally to the distribution system, the tap. Generally, the tap waters experienced little lag time in the managed system, having a residence time of about two months. Tap and reservoir waters preserved the precipitation signal with the reservoir morphology acting as an important control. These water supply reservoirs functioned more like a river system with a faster throughput of water and larger variations in chemical parameters. Other water supply reservoirs have a greater capacity with a larger amount of water supply usage through a more lacustrine environment, which displays more constant solute concentrations and longer flow-through times. This work provides a basic understanding of a regional water supply system in central Ohio, reservoir isotopic dynamics, and Ohio precipitation sources.

}, keywords = {LTER-MCM, Antarctica, boron isotopes, hyporheic zone, McMurdo Dry Valleys, Ohio precipitation source, oxygen-18 and deuterium isotopes, saline lake}, url = { http://rave.ohiolink.edu/etdc/view?acc_num=osu1386000037}, author = {Leslie, D.L. and W. Berry Lyons} } @mastersthesis {4093, title = {Resource Legacies and Priming Regulate Microbial Communities in Antarctica{\textquoteright}s Dry Valleys}, volume = {M.S.}, year = {2013}, school = {Brigham Young University}, type = {masters}, address = {Provo, UT}, abstract = {

Multiple mechanisms control bacterial community structure but two in particular, the \"legacy\" of past environmental conditions, and the \"priming\" of bacteria to respond to seasonal or reoccurring fluctuations in resources, have the potential to determine both bacterial communities, as well as, temporal shifts in active bacterial taxa. To begin to evaluate the legacy effects of resources on microbial communities, we added four limiting resources annually (i.e., water only; C-mannitol + water; N-NH4NO3 + water; and C, N + water) and measured shifts in bacterial community composition after seven years in a cold desert ecosystem in the McMurdo Dry Valleys, Antarctica. Further, to investigate the ecological significance of priming, we conducted a series of stable isotope probing experiments (i.e., 18O-DNA SIP with 18O-labeled water, 13C-DNA SIP with 13C-labeled mannitol, 15N-DNA with 15N- NH4NO3, and a combined C and N SIP) and characterized the responding (i.e., isotopically labeled) and seed bank (i.e., unlabeled) bacterial communities. We performed each of the SIPs in soil microcosms corresponding to a single resource manipulation (e.g., 13C-labeled mannitol in C addition soils). We hypothesized that all long-term additions of nutrients and water will lead to a distinct bacterial community\—a legacy effect due to the nutrient and water impoverished state of Antarctica soils. We also hypothesized that the stronger the legacy effects demonstrated by a specific community the more adapted or primed bacterial species will be to take advantage of the resource and respond. As hypothesized, resource additions created distinct bacterial legacy but to different degrees among the treatments. The extent of the resource legacy effects was greatest in the CN, intermediate in water and N, and lowest in C communities relative to the control communities, suggesting that C induced changes in communities were intensified by tandem N additions and that water alone created a more distinct legacy than water and C additions combined. Contrary to our hypothesis, the stronger the legacy effects, the less adapted or primed the community was to take advantage of resource additions. For example, the CN treatment that induced the greatest effect on bacterial communities had the lowest number of species (20.9\%) in common between the responding and seed bank communities. This inverse relationship may be due to only two species (i.e., Arthrobacter, Actinobacteria and Massilia, Betaproteobacteria) really being primed to take advantage of CN and these species constituting over 75\% of the seed bank community. Water, N, and C additions had similar levels of priming with 38.4\%, 41.4\%, and 36.3\% of the responding species being present in the seed bank community, respectively. But of these three treatments, only the priming with water resulted in a unique responding community, suggesting that water, a universal bacterial resource, was enough to prime bacteria. Furthermore, water generates the most diverse responding community of all the resources with stemming from all of the fourteen dominant phyla. We did find patterns of ecological coherence among the responders, especially in the major responders (i.e., responders that increased in relative recovery by at least ten-fold). These responders were predominantly found in only three phyla (i.e., Actinobacteria, Bacteriodetes, and Gammaproteobacteria) regardless of resource addition. Alternatively minor responders (i.e., responders that increased in relative recovery at least two-fold) were contained in fourteen different phyla with specific taxa stimulated by CN (i.e., Betaproteobacteria) and N and water (i.e., Deltaproteobacteria). Further, resource additions elicited responses from 37\% of bacterial species with species specializing on a specific resource (e.g., Chloroflexi) or being a generalist (e.g., Planctomycetes and Gammaproteobacteria). Our results offer the first direct links between legacy and priming effects on bacterial community composition and demonstrate that these mechanisms are not always complimentary leading to the formation of similar communities but may both be essential to maintain the high levels of bacterial diversity. Further, all resources produced elicited responders that were either specialists of generalists demonstrating that even bacteria in the extreme environment of Antarctica respond to pulses of resources.

}, keywords = {LTER-MCM, 454 pyrosequencing, Antarctica, bacteria, microbial ecology, soil, soil ecology, stable isotope probing, target metagenomics}, url = {http://hdl.lib.byu.edu/1877/etd6229}, author = {Saurey, Sabrina D.}, editor = {Aanderud, Zachary T.} } @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} } @mastersthesis {4163, title = {Hydrologic controls of nutrient fluxes in glacial meltwater streams at inter-annual, seasonal, and daily timescales in the McMurdo Dry Valleys, Antarctica}, volume = {M.S.}, year = {2011}, school = {Pennsylvania State University}, type = {masters}, abstract = {

In the McMurdo Dry Valleys of Antarctica, glaciers are hydrologically linked to closed-basin lakes at the valley floor by glacial meltwater streams. Streams flow through porous, well-defined channels with extensive chemically active hyporheic zones. Temporally varying dynamics of meltwater generation and sub-stream thaw depth are thought to control the potential for the hyporheic zone and benthic communities to influence transport of nutrients and dissolved ions downstream. Using the McMurdo LTER database, patterns in stream discharge, electrical conductivity (both with 15-minute sampling intervals), and solute chemistry (weekly sampling intervals) were examined on eight MDV streams from 1990-2008. Discharge and electrical conductivity values were highly variable among streams. Discharge values were highly dependent upon glacial source area, but meteorological and topographical complexities create large variability at all time scales. The longer streams were found to have much higher electrical conductivity values than the shorter streams, suggesting that there are more opportunities for hyporheic weathering reactions along longer stream reaches. Weekly sampled water solutes from each stream\&$\#$39;s entire record were plotted against the discharge recorded at the time when the sample was taken. Silicate concentrations displayed a decreasing logarithmic relationship, while nutrient concentrations had no apparent relationship. This suggests that with the exception to bioreactive solutes, the majority of hyporheic interactions could possibly be characterized by electrical conductivity and discharge. To attain information on in-stream nutrient dynamics and nutrient fluxes, glacial source water at the upper reach of Green Creek and stream outlet water at the lower reach of Green Creek were sampled hourly for two separate diel periods during the 2008-09 austral summer. Both dates were in late January under two distinct flow conditions (~0.5 L/s and ~10 L/s). Under low flow conditions, nutrient cycling was found to be uptake dominated. High flow conditions showed both uptake and regeneration with much higher nutrient loads, but as in the low flow conditions, no apparent temporal trends were found. Nutrient concentrations could not be predicted using the two parameters of discharge and electrical conductivity with in-stream nutrient dynamics likely too complicated at the sub-daily scale.

}, keywords = {LTER-MCM, Antarctica, biogeochemistry, chemical weathering, discharge, electrical conductivity, glacial melt, glaciers, hydrology, hyporheic, MCM LTER, McMurdo Dry Valleys, nutrient fluxes, nutrients, polar desert, solute chemistry, stream chemistry, streamflow, water chemistry}, url = {https://etda.libraries.psu.edu/catalog/11568}, author = {Weaver, Mitchell R. and Michael N. Gooseff} } @mastersthesis {4366, title = {Aeolian sediments of the McMurdo Dry Valleys, Antarctica}, volume = {M.S.}, year = {2010}, school = {Ohio State University}, type = {masters}, address = {Columbus, OH}, abstract = {

The role of dust has become a topic of increasing interest in the interface between climate and geological/ecological sciences. Dust emitted from major sources, the majority of which are desert regions in the Northern Hemisphere, is transported via suspension in global wind systems and incorporated into the biogeochemical cycles of the ecosystems where it is ultimately deposited. While emissions within the McMurdo Dry Valleys (MDV) region of Antarctica are small compared to other source regions, the redistribution of new, reactive material by wind may be important to sustaining life in the ecosystem.


The interaction of the dry, warm foehn winds and the cool, moist coastal breezes \“recycles\” soil particles throughout the landscape. The bulk of sediment movement occurs during foehn events in the winter that redistribute material throughout the MDV. To understand the source and transfer of this material samples were collected early in the austral summer (November 2008) prior to the initiation of extensive ice melt from glacial and lake surfaces, aeolian landforms, and elevated sediment traps. These were preserved and processed for grain size distribution and major element composition at the sand and silt particle sizes. Major elemental oxide analysis indicated that the silt and sand size particles are of different composition: SiO2 values for silt range from 50 to 59\% by weight and for sand range from 59 to 74\%. When compared to the elemental oxide composition four rock types present in the MDV, the composition of the silt indicates a mixing influenced mostly by the igneous rock types (Ferrar Dolerite and McMurdo Volcanic basanite) and sand a mixing influenced largely by the sedimentary rocks (Beacon Sandstone and the metasedimentary Basement Complex). This could imply a local source of the aeolian material that is corroborated by low CIA values at both particle sizes (44-57\%) indicating low degrees of chemical weathering. In addition, comparison of 87Sr/86Sr and 143Nd/144Nd to values published for the major MDV rock types and ice core dust to values analyzed in 3 silt size glacier sample and one bulk glacier sample also indicates a local source of sediments and that it is not likely to be transferred inland.


During the melt season, the aeolian material is actively solubilized where it interacts with water, releasing solutes and vital bioavailable nutrients throughout the aquatic system. Differences in the chemistry of supra- and proglacial streams as well as lake surface waters may be derived from the deposition and dissolution of these aeolian sediments. To simulate these conditions, a two-step leaching method using deionized water to represent glacial melt in field conditions was employed and leachates analyzed for major ion and nutrient constituents. Leachates represent a small degree (\<0.7\%) of dissolution of major elements, and are solubilized to a greater extent from samples closer to the coast or with increased silt content. The composition of the leachates reflects the dissolution of the major salts found in the MDV. Leach 1 (cold water) indicates that Na- and Cl-bearing salt phases are dissolved to a greater extent than seen in Leach 2 (freeze-thaw). Conversely, Leach 2 compositions indicate that carbonate mineral dissolution and Mg-bearing silicate weathering are proceeding to a greater extent than in Leach 1.


Inorganic N:P ratios follow the same patterns of nutrient limitations based on the Redfield Ratio found by Priscu (1995) in the terminal lakes of the Taylor Valley: N-limited in the Fryxell and Hoare basins (east) and P-limited in the Bonney basin (west). This is also consistent with the age of the tills in the area, as found by Gudding (2003). The concentration of soluble Fe in the leachates is about the same as soluble inorganic P, and thus is not a limiting nutrient in the leachates. Comparison of total dissolved N and P to their inorganic counterparts reveals increased organic nutrients in the glacier and lake leachates that may indicate the influence of biota. Nutrient fluxes based on known sediment fluxes from elevated sediment traps deployed throughout the MDV and the composition of these leachates range from 0.34-330 g a-1 for N, 0.02-8.3 g a-1 for P, and 0.03-8.6 g a-1 for Fe. These are at least two orders of magnitude less than calculated loads from streams to the lakes in the Taylor Valley and, thus, should be considered underestimations or minima.


This work provides the first investigation into the composition and source of aeolian transported materials in the MDV, as well of what is potentially solubilized from it during the austral summer melt season. In addition, it will contribute to the understanding of the interplay between aeolian and aquatic processes in the MDV and further the understanding of this unique ecosystem.

}, keywords = {LTER-MCM, aeolian transport, Antarctica, dust, experimental leaching, geochemistry, McMurdo Dry Valleys, sediment provenance, weathering}, url = {http://rave.ohiolink.edu/etdc/view?acc_num=osu1290524862}, author = {Deuerling, Kelly M. and W. Berry Lyons} } @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 {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} }