@article {4864, title = {Nitrogen fixation facilitates stream microbial mat biomass across the McMurdo Dry Valleys, Antarctica}, journal = {Biogeochemistry}, year = {2023}, month = {07/2023}, abstract = {

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

}, keywords = {LTER-MCM, biofilm, C, cyanobacteria, hyporheic zone, MCM LTER, mineralization, N, P biogeochemistry}, doi = {10.1007/s10533-023-01069-0}, url = {https://link.springer.com/article/10.1007/s10533-023-01069-0}, author = {Tyler J. Kohler and Singley, Joel G. and Wlostowski, Adam and Diane M. McKnight} } @article {4489, title = {Nutrient uptake in the supraglacial stream network of an Antarctic glacier}, journal = {Journal of Geophysical Research: Biogeosciences}, year = {2020}, month = {08/2020}, abstract = {

In polar regions, where many glaciers are cold-based (frozen to their beds), biological communities on the glacier surface can modulate and transform nutrients, controlling downstream delivery. However, it remains unclear whether supraglacial streams are nutrient sinks or sources and the rates of nutrient processing. In order to test this, we conducted tracer-injections in three supraglacial streams (62 to 123 m long) on Canada Glacier in the Taylor Valley, of the McMurdo Dry Valleys, Antarctica. We conducted a series of additions including: nitrate (N), N + phosphate (P), N+ P + glucose (C), and N+C. In two reaches, N-only additions resulted in N uptake. The third reach showed net N release during the N-only addition, but high N uptake in the N+P addition, indicating P-limitation or N+P co-limitation. Co-injecting C did not increase N-uptake. Additionally, in these systems at low N concentrations the streams can be a net source of nitrogen. We confirmed these findings using laboratory-based nutrient incubation experiments on sediment collected from stream channels on Canada Glacier and two other glaciers in the Taylor Valley. Together, these results suggest there is active biological processing of nutrients occurring in these supraglacial streams despite low sediment cover, high flow velocities and cold temperatures, modifying the input signals to proglacial streams. As glaciers world-wide undergo rapid change, these findings further our understanding of how melt generated on glacier surfaces set the initial nutrient signature for subglacial and downstream environments.

}, keywords = {LTER-MCM, McMurdo Dry Valleys, nitrogen, nutrient tracers, nutrient uptake, sediments, supraglacial streams}, doi = {10.1029/2020JG005679}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JG005679}, author = {Bergstrom, Anna J. and Michael N. Gooseff and Singley, Joel G. and Cohen, Matthew J. and Kathleen A. Welch} } @article {4164, title = {Nematodes in a polar desert reveal the relative role of biotic interactions in the coexistence of soil animals}, journal = {Communications Biology}, volume = {2}, year = {2019}, month = {02/2019}, abstract = {

Abiotic factors are major determinants of soil animal distributions and their dominant role is pronounced in extreme ecosystems, with biotic interactions seemingly playing a minor role. We modelled co-occurrence and distribution of the three nematode species that dominate the soil food web of the McMurdo Dry Valleys (Antarctica). Abiotic factors, other biotic groups, and autocorrelation all contributed to structuring nematode species distributions. However, after removing their effects, we found that the presence of the most abundant nematode species greatly, and negatively, affected the probability of detecting one of the other two species. We observed similar patterns in relative abundances for two out of three pairs of species. Harsh abiotic conditions alone are insufficient to explain contemporary nematode distributions whereas the role of negative biotic interactions has been largely underestimated in soil. The future challenge is to understand how the effects of global change on biotic interactions will alter species coexistence.

}, keywords = {LTER-MCM}, doi = {10.1038/s42003-018-0260-y}, url = {http://www.nature.com/articles/s42003-018-0260-y}, author = {Caruso, Tancredi and Hogg, Ian D. and Uffe N. Nielsen and Bottos, Eric M. and Charles K. Lee and D. W. Hopkins and Craig S Cary and John E. Barrett and Green, T. G. Allan and Storey, Bryan C. and Diana H. Wall and Byron Adams} } @article {4068, title = {Near-surface refractory black carbon observations in the atmosphere and snow in the McMurdo Dry Valleys, Antarctica and potential impacts of foehn winds}, journal = {Journal of Geophysical Research: Atmospheres}, volume = {123}, year = {2018}, month = {01/2018}, pages = {2877 - 2887}, abstract = {

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

}, keywords = {LTER-MCM}, doi = {10.1002/2017JD027696}, url = {http://doi.wiley.com/10.1002/2017JD027696}, author = {Khan, Alia L. and McMeeking, Gavin and Schwarz, Joshua P. and Xian, Peng and Kathleen A. Welch and W. Berry Lyons and Diane M. McKnight} } @article {4103, title = {Niche specialization of bacteria in permanently ice-covered lakes of the McMurdo Dry Valleys, Antarctica}, journal = {Environmental Microbiology}, volume = {19}, year = {2017}, month = {06/2017}, pages = {2258 - 2271}, abstract = {

Perennially ice-covered lakes in the McMurdo Dry Valleys, Antarctica, are chemically stratified with depth and have distinct biological gradients. Despite long-term research on these unique environments, data on the structure of the microbial communities in the water columns of these lakes are scarce. Here, we examined bacterial diversity in five ice-covered Antarctic lakes by 16S rRNA gene-based pyrosequencing. Distinct communities were present in each lake, reflecting the unique biogeochemical characteristics of these environments. Further, certain bacterial lineages were confined exclusively to specific depths within each lake. For example, candidate division WM88 occurred solely at a depth of 15 m in Lake Fryxell, whereas unknown lineages of\ Chlorobi\ were found only at a depth of 18 m in Lake Miers, and two distinct classes of\ Firmicutes\ inhabited East and West Lobe Bonney at depths of 30 m. Redundancy analysis revealed that community variation of bacterioplankton could be explained by the distinct conditions of each lake and depth; in particular, assemblages from layers beneath the chemocline had biogeochemical associations that differed from those in the upper layers. These patterns of community composition may represent bacterial adaptations to the extreme and unique biogeochemical gradients of ice-covered lakes in the McMurdo Dry Valleys.

}, keywords = {LTER-MCM}, doi = {10.1111/emi.2017.19.issue-610.1111/1462-2920.13721}, url = {https://onlinelibrary.wiley.com/doi/pdf/10.1111/1462-2920.13721}, author = {Kwon, Miye and Kim, Mincheol and Cristina D. Takacs-Vesbach and Lee, Jaejin and Hong, Soon Gyu and Kim, Sang Jong and John C. Priscu and Kim, Ok-Sun} } @mastersthesis {4067, title = {Nitrate Dynamics Under Unsteady and Intermittent Flow in an Antarctic Stream}, volume = {M.S.}, year = {2017}, school = {University of Colorado at Boulder}, type = {masters}, abstract = {

Low order streams are a primary vector and modulator for the transport of anthropogenically derived reactive nitrogen, especially as nitrate (NO3\–). A large proportion of low orders streams experience short-term unsteady and intermittent flow conditions, and the prevalence of these dynamics is likely to increase due to climate change and human management. While such hydrologic variability is recognized as an important first-order control on the transport of NO3\–, prior reliance on manual sampling has resulted in a disparity between our understanding physical and hydrochemical dynamics at short-timescales, such that a large gap exists in our understanding of how unsteady and intermittent sub-daily discharge affects instream NO3\– transport patterns. To address this challenge, I used in situ sensors to collect high-frequency (i.e., 15 minute) NO3\– concentration and discharge data in an ephemeral, oligotrophic glacial meltwater stream in the McMurdo Dry Valleys, Antarctica. I analyzed concentration-discharge relationships using a power-law framework to identify a flow threshold that governed NO3\– transport dynamics. I observed relative chemostasis of NO3\– during large magnitude diel flood pulsing events. This suggests that biological and physical processes controlling the transport and transformation of NO3\–, and N more generally, are likely to exhibit spatial and temporal variability at very short timescales in response to extreme hydrologic variability. Such spatiotemporal variability in N processing dynamics has not been included in prior conceptual models of N cycling in MDV streams. As such, I propose a conceptual model in which short-term flow pulsing and cessation shift sediment redox conditions and microbial processes such that the shallow hyporheic zone temporally becomes a net source and storage zone for a spatially distributed pool of NO3\–. The results of this approach will inform understanding of how highly variable hydrological conditions measured at very short timescales interacts with instream biogeochemical processes to control N transport.

}, keywords = {LTER-MCM}, url = {http://search.proquest.com/openview/88a6ce6614e2a0cfc757c8fd7a887504/1?pq-origsite=gscholar\&cbl=18750\&diss=y}, author = {Singley, Joel G.}, editor = {Eve-Lyn S. Hinckley} } @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} } @article {3959, title = {Nutrient treatments alter microbial mat colonization in two glacial meltwater streams from the McMurdo Dry Valleys, Antarctica}, journal = {FEMS Microbiology Ecology}, volume = {92}, year = {2016}, month = {03/2016}, pages = {fiw049}, abstract = {

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

}, keywords = {LTER-MCM}, doi = {10.1093/femsec/fiw049}, url = {http://femsec.oxfordjournals.org/lookup/doi/10.1093/femsec/fiw049}, author = {Tyler J. Kohler and David J. Van Horn and Darling, Joshua P. and Cristina D. Takacs-Vesbach and Diane M. McKnight}, editor = {Wagner, Dirk} } @article {3522, title = {Niche and metabolic principles explain patterns of diversity and distribution: theory and a case study with soil bacterial communities}, journal = {Proceedings of the Royal Society B: Biological Sciences}, volume = {282}, year = {2015}, month = {05/2015}, pages = {2630}, abstract = {

The causes of biodiversity patterns are controversial and elusive due to complex environmental variation, covarying changes in communities, and lack of baseline and null theories to differentiate straightforward causes from more complex mechanisms. To address these limitations, we developed general diversity theory integrating metabolic principles with niche-based community assembly. We evaluated this theory by investigating patterns in the diversity and distribution of soil bacteria taxa across four orders of magnitude variation in spatial scale on an Antarctic mountainside in low complexity, highly oligotrophic soils. Our theory predicts that lower temperatures should reduce taxon niche widths along environmental gradients due to decreasing growth rates, and the changing niche widths should lead to contrasting α- and β-diversity patterns. In accord with the predictions, α-diversity, niche widths and occupancies decreased while β-diversity increased with increasing elevation and decreasing temperature. The theory also successfully predicts a hump-shaped relationship between α-diversity and pH and a negative relationship between α-diversity and salinity. Thus, a few simple principles explained systematic microbial diversity variation along multiple gradients. Such general theory can be used to disentangle baseline effects from more complex effects of temperature and other variables on biodiversity patterns in a variety of ecosystems and organisms.

}, keywords = {LTER-MCM}, issn = {0962-8452}, doi = {10.1098/rspb.2014.2630}, url = {http://rspb.royalsocietypublishing.org/lookup/doi/10.1098/rspb.2014.2630}, author = {Okie, Jordan G. and David J. Van Horn and Storch, David and John E. Barrett and Michael N. Gooseff and Kopsova, Lenka and Cristina D. Takacs-Vesbach} } @article {1068, title = {Near-Surface Internal Melting - a Substantial Mass Loss on Antarctic Dry Valley Glaciers.}, journal = {Journal of Glaciology}, volume = {60}, year = {2014}, month = {04/2014}, pages = {361-374}, chapter = {361}, abstract = {The McMurdo Dry Valleys, southern Victoria Land, East Antarctica, are a polar desert, and melt from glacial ice is the primary source of water to streams, lakes and associated ecosystems. Previous work found that to adequately model glacier ablation and subsurface ice temperatures with a surface energy-balance model required including the transmission of solar radiation into the ice. Here we investigate the contribution of subsurface melt to the mass balance of (and runoff from) Dry Valley glaciers by including a drainage process in the model and applying the model to three glacier sites using 13years of hourly meteorological data. Model results for the smooth glacier surfaces common to many glaciers in the Dry Valleys showed that sublimation was typically the largest component of surface lowering, with rare episodes of surface melting, consistent with anecdotal field observations. Results also showed extensive internal melting 5-15 cm below the ice surface, the drainage of which accounted for 50\% of summer ablation. This is consistent with field observations of subsurface streams and formation of a weathering crust. We identify an annual cycle of weathering crust formation in summer and its removal during the 10 months of winter sublimation.}, keywords = {LTER-MCM}, doi = {10.3189/2014JoG13J095}, author = {Hoffman, M and Andrew G Fountain and Liston, G} } @article {1126, title = {Nematode communities of Byers Peninsula, Livingston Island, maritime Antarctica}, journal = {Antarctic Science}, volume = {23}, year = {2011}, month = {8/2011}, pages = {349 - 357}, keywords = {LTER-MCM}, doi = {10.1017/S0954102011000174}, author = {Uffe N. Nielsen and Diana H. Wall and Li, Grace and Toro, Manuel and Byron Adams and Ross A. Virginia} } @article {1167, title = {New insights into the origin and evolution of Lake Vida, McMurdo Dry Valleys, Antarctica {\textemdash} A noble gas study in ice and brines}, journal = {Earth and Planetary Science Letters}, volume = {289}, year = {2010}, month = {01/2010}, pages = {112 - 122}, keywords = {LTER-MCM}, doi = {10.1016/j.epsl.2009.10.034}, url = {http://www.sciencedirect.com/science/article/pii/S0012821X09006335}, author = {Jessica L. Malone and Clara M. Castro and Chris M. Hall and Peter T. Doran and Kenig, Fabien and Christopher P. McKay} } @inbook {1337, title = {The need for understanding how biodiversity and ecosystem functioning affect ecosystem services in soil and sediments}, booktitle = {Sustaining Biodiversity and Ecosystem Services in Soils Sediments}, year = {2004}, publisher = {Island Press}, organization = {Island Press}, keywords = {LTER-MCM}, author = {Diana H. Wall and Richard D. Bardgett and Covich, A and P.V.R. Snelgrove}, editor = {Diana H. Wall} } @inbook {1436, title = {Nematodes - Pervading The Earth and Linking All Life}, booktitle = {Nature and Human Society: The Quest for a Sustainable World}, year = {2000}, pages = {176-191}, publisher = {Committee for the Second Forum on Biodiversity, National Academy of Sciences and National Research Council}, organization = {Committee for the Second Forum on Biodiversity, National Academy of Sciences and National Research Council}, keywords = {LTER-MCM}, author = {Baldwin, J.G. and Nadler, S and Diana H. Wall}, editor = {Tania Williams and Peter H. Raven} } @article {1442, title = {Nuclear and mitochondrial DNA sequence diversity in the Antarctic nematode Scottnema lindsayae}, journal = {Journal of Nematology}, volume = {322}, year = {2000}, pages = {143-153}, keywords = {LTER-MCM}, author = {Courtright, E and Diana H. Wall and Ross A. Virginia and Vida, J and Frisse, L and Thomas, W} } @article {1518, title = {Natural abundance of carbon and nitrogen isotopes in potential sources of organic matter to soils of Taylor Valley, Antarctica}, journal = {Antarctic Journal of the United States - 1996 Review Issue (NSF 98-28)}, volume = {31}, year = {1998}, pages = {209-210}, keywords = {LTER-MCM}, author = {Melody B. Burkins and C. Page Chamberlain and Ross A. Virginia and Diana W. Freckman} } @article {1519, title = {Nitrogen fixation within permanent ice covers on lakes in the McMurdo Dry Valleys, Antarctica}, journal = {Antarctic Journal of the United States - 1996 Review Issue (NSF 98-28)}, volume = {31}, year = {1998}, pages = {218-220}, keywords = {LTER-MCM}, author = {Amanda M. Grue and Christian H. Fritsen and John C. Priscu} } @article {1623, title = {Natural Fluorescence and Quantum Yields in Vertically Stationary Phytoplankton from Perennially Ice-Covered Lakes}, journal = {Limnol. Oceanogr.}, volume = {39}, year = {1994}, pages = {1399-1410}, keywords = {LTER-MCM}, author = {Michael P. Lizotte and John C. Priscu} } @article {1624, title = {Nematode biodiversity and community structure in Antarctic Polar Desert Soils}, journal = {Bulletin of the Ecological Society of America}, volume = {75}, year = {1994}, pages = {186}, keywords = {LTER-MCM, Biggie}, author = {Powers, Laura E. and Diana W. Freckman and Ross A. Virginia} } @inbook {1625, title = {Nematode biodiversity and survival in Antarctic Dry Valley soils}, booktitle = {SCAR 6th Biology Symposium}, year = {1994}, address = {Venice, Italy}, keywords = {LTER-MCM}, author = {Diana W. Freckman and Ross A. Virginia and Powers, Laura E.} } @article {1641, title = {Nitrifying and denitrifying bacteria in Lake Bonney}, journal = {Antarctic Journal of the U.S.}, volume = {28}, year = {1993}, pages = {239-241}, keywords = {LTER-MCM}, author = {Bess B. Ward and Cockcroft, A.R. and John C. Priscu} } @article {1649, title = {Nematodes and soil properties in the Dry Valleys of southern Victoria Land, Antarctica}, journal = {Bulletin of the Ecological Society of America}, volume = {73}, year = {1992}, pages = {179}, keywords = {LTER-MCM}, author = {Diana W. Freckman and Ross A. Virginia} } @article {1650, title = {Nematodes in Antarctic Dry Valley soils: extraction and distribution}, journal = {Journal of Nematology}, volume = {24}, year = {1992}, pages = {591}, keywords = {LTER-MCM}, author = {Diana W. Freckman and Ross A. Virginia} } @article {1653, title = {Nematodes in the McMurdo Dry Valleys of Southern Victoria Land}, journal = {Antarctic Journal of the United States}, volume = {26}, year = {1991}, pages = {233-234}, keywords = {LTER-MCM}, doi = {LTER}, author = {Diana W. Freckman and Ross A. Virginia} } @article {1656, title = {Nematode Ecology of the McMurdo Dry Valley Ecosystems}, journal = {Antarctic Journal of the United States}, volume = {25}, year = {1990}, pages = {229-230}, keywords = {LTER-MCM}, doi = {LTER}, author = {Diana W. Freckman and Ross A. Virginia} }