Open AccessCatch and release: Hyporheic retention and mineralization of N‐fixing Nostoc sustains downstream microbial mat biomass in two polar desert streams
Author(s) -
Kohler Tyler J.,
Stanish Lee F.,
Liptzin Daniel,
Barrett John E.,
McKnight Diane M.
Publication year - 2018
Publication title -
limnology and oceanography letters
Language(s) - English
Resource type - Journals
ISSN - 2378-2242
DOI - 10.1002/lol2.10087
Subject(s) - organic matter , mineralization (soil science) , streams , hyporheic zone , environmental chemistry , nutrient , environmental science , meltwater , nostoc , glacier , ecology , chemistry , cyanobacteria , biology , soil water , bacteria , computer network , paleontology , computer science , genetics
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.