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Coupled Cycles of Dissolved Oxygen and Nitrous Oxide in Rivers along a Trophic Gradient in Southern Ontario, Canada
Author(s) -
Rosamond Madeline S.,
Thuss Simon J.,
Schiff Sherry L.,
Elgood Richard J.
Publication year - 2011
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2010.0009
Subject(s) - diel vertical migration , nitrous oxide , cycling , trophic level , environmental chemistry , environmental science , denitrification , nitrogen , ecosystem , water column , nitrite , chemistry , ecology , atmospheric sciences , hydrology (agriculture) , nitrate , biology , geology , geotechnical engineering , archaeology , organic chemistry , history
Diel (24‐h) cycling of dissolved O 2 (DO) in rivers is well documented, but evidence for coupled diel changes in DO and nitrogen cycling has only been demonstrated in hypereutrophic systems where DO approaches zero at night. Here, we show diel changes in N 2 O and DO concentration at several sites across a trophic gradient. Nitrous oxide concentration increased at night at all but one site in spring and summer, even when gas exchange was rapid and minimum water column DO was well above hypoxic conditions. Diel N 2 O curves were not mirror images of DO curves and were not symmetrical about the mean. Although inter‐ and intrasite variation was high, N 2 O peaked around the time of lowest DO at most of the sites. These results suggest that N 2 O must be measured several times per diel period to characterize curve shape and timing. Nitrous oxide concentration was not significantly correlated with NO 3 − concentration, contrary to studies in agricultural streams and to the current United Nations Intergovernmental Panel for Climate Change protocols for N 2 O emission estimation. The strong negative correlation between N 2 O concentration and daily minimum DO concentration suggested that N 2 O production was limited by DO. This is consistent with N 2 O produced by nitrite reduction. The ubiquity of diel N 2 O cycling suggests that most DO and N 2 O sampling strategies used in rivers are insufficient to capture natural variability. Ecosystem‐level effects of microbial processes, such as denitrification, are sensitive to small changes in redox conditions in the water column even in low‐nutrient oxic rivers, suggesting diel cycling of redox‐sensitive compounds may exist in many aquatic systems.