An intense precipitation event causes a temperate forested drainage network to shift from <scp>N<sub>2</sub>O</scp> source to sink
Kelly S. Aho, Jennifer H. Fair, Jacob D. Hosen, Ethan D. Kyzivat, Laura Logozzo, L. Weber, Byungman Yoon, Jay P. Zarnetske, Peter A. Raymond
Abstract
Abstract Nitrous oxide (N 2 O) evasion from streams and rivers is a significant, yet highly uncertain, flux in nitrogen cycle models. Most global estimates of lotic N 2 O emission assume that evasion rates are proportional to inorganic nitrogen inputs to a stream or river. However, many field studies do not detect relationships between lotic N 2 O evasion and dissolved nitrogen concentration, highlighting the need for better understanding of process‐based controls on this flux. This study reports 4‐yr time series of p N 2 O and N 2 O evasion from eight nested streams and rivers and detects an abrupt change in N 2 O dynamics associated with an intense rainstorm. This rainstorm, and the associated hydrologic flood event, pushed forested reaches across the watershed from consistent N 2 O sources to prolonged N 2 O sinks. We attribute this shift to disturbance of incomplete denitrification in the stream network and surrounding watershed, although alternate hypotheses are also discussed. There was continued availability of nitrate ( ) for in‐stream processing, eliminating the possibility that ‐availability limited N 2 O production, and post‐storm N 2 O‐to‐nitrate ratios were lower than pre‐storm ratios suggesting that the large storm affected in‐situ nitrogen processing rates. The sustained period of post‐storm N 2 O undersaturation resulted in net negative evasion for five of the eight study sites in 2018, which mitigated emissions over the 4‐yr study. This nonlinear response in N 2 O dynamics illustrates the potential importance of storm events to control lotic N 2 O production and emissions.