%0 Journal Article %J Limnology and Oceanography Letters %D 2018 %T Catch and release: Hyporheic retention and mineralization of N-fixing Nostoc sustains downstream microbial mat biomass in two polar desert streams %A Tyler J. Kohler %A Lee F. Stanish %A Liptzin, D. %A John E. Barrett %A Diane M. McKnight %X

 

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

 

%B Limnology and Oceanography Letters %V 3 %P 357 - 364 %8 07/2018 %G eng %U https://aslopubs.onlinelibrary.wiley.com/doi/abs/10.1002/lol2.10087 %N 4 %! Limnol. Oceanogr. %R 10.1002/lol2.10087 %0 Journal Article %J Ecosystems %D 2015 %T Long-Term Hydrologic Control of Microbial Mat Abundance in McMurdo Dry Valley Streams, Antarctica. %A Tyler J. Kohler %A Lee F. Stanish %A Stenven Crisp %A Koch, J. %A Liptzin, D. %A Baeseman, J. %A Diane M. McKnight %X

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

%B Ecosystems %V 18 %P 310-327 %8 03/2015 %G eng %U http://link.springer.com/article/10.1007%2Fs10021-014-9829-6 %N 2 %& 310