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Understanding pathways of dissimilatory and assimilatory dissolved inorganic nitrogen uptake in streams
Author(s) -
Ribot M.,
von Schiller D.,
Martí E.
Publication year - 2017
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.1002/lno.10493
Subject(s) - environmental chemistry , nitrogen cycle , nitrate , streams , context (archaeology) , ecosystem , ammonium , nitrification , denitrification , nitrogen , chemistry , biogeochemical cycle , ecology , biology , computer network , paleontology , organic chemistry , computer science
Dissolved inorganic nitrogen (DIN) in streams is mostly available as two different species: nitrate (NO 3 −) and ammonium (NH 4 +). These two DIN species undergo specific dissimilatory uptake pathways and show distinct preference during biological assimilation. These differences ultimately dictate how DIN is cycled within streams and its further export to downstream ecosystems. Here, we provide a synthesis analysis of the uptake ofNO 3 −andNH 4 +at the reach scale and on the contribution of dissimilatory and assimilatory uptake pathways. We combined 15 N‐tracer experiments in a single stream with compiled results ofNO 3 −andNH 4 +uptake from the literature. As expected, streams were more efficient in processingNH 4 +thanNO 3 −at the reach scale. These results were partially explained by the fact that, on average, dissimilatoryNO 3 −uptake (i.e., denitrification and DNRA) had a low incidence on totalNO 3 −uptake, whereas dissimilatoryNH 4 +uptake (i.e., nitrification) contributed to a high proportion of totalNH 4 +uptake thereby increasing in‐streamNO 3 −concentration. Furthermore, assimilatory uptake by in‐stream biotic compartments dominated the total uptake of the two DIN species and was generaly higher forNH 4 +than forNO 3 −. Overall, results from this study indicate that assimilatory uptake by biotic compartments rather than permanent removal dominates totalNO 3 −uptake in streams. In contrast, both assimilatory and dissimilatory uptake can contribute similarly to totalNH 4 +uptake. Our findings have strong implications for a better understanding of N cycling within the context of widespread increases in DIN concentration and changes in theNO 3 − : NH 4 +ratio driven by human activities.