Catch and release: Hyporheic retention and mineralization of N‐fixing Nostoc sustains downstream microbial mat biomass in two polar desert streams

• Published in: Limnology and Oceanography Letters
• Main Authors: Kohler, Tyler J., Stanish, Lee F., Liptzin, Daniel, Barrett, John E., McKnight, Diane M.
• Other Authors: Office of Polar Programs
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2018
• Subjects: polar desert
• Online Access: http://dx.doi.org/10.1002/lol2.10087; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Flol2.10087; https://onlinelibrary.wiley.com/doi/pdf/10.1002/lol2.10087; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/lol2.10087; http://api.wiley.com/onlinelibrary/chorus/v1/articles/10.1002%2Flol2.10087; https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.1002/lol2.10087

Abstract Much work has been performed to investigate controls on nitrogen (N) uptake in streams, yet the fate of assimilated N is comparatively poorly resolved. Here, we use in‐stream fixed N as an isotopic tracer to study the fate of assimilated N in glacial meltwater streams. We characterized δ 15 N 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 (δ 15 N ≅ 0‰), suggesting N‐fixation. Other mat types were depleted upstream, and became progressively enriched downstream (plateauing at δ 15 N ≅ 0‰), 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.