Abstract
Sea level rise will change inundation regimes in salt marshes, altering redox dynamics that control nitrification – a potential source of the potent greenhouse gas, nitrous oxide (N 2 O) – and denitrification, a major nitrogen (N) loss pathway in coastal ecosystems and both a source and sink of N 2 O. Measurements of net N 2 O fluxes alone yield little insight into the different effects of redox conditions on N 2 O production and consumption. We used in situ measurements of gross N 2 O fluxes across a salt marsh elevation gradient to determine how soil N 2 O emissions in coastal ecosystems may respond to future sea level rise. Soil redox declined as marsh elevation decreased, with lower soil nitrate and higher ferrous iron in the low marsh compared to the mid and high marshes ( P P 2 O fluxes differed significantly among marsh zones ( P = 0.009), averaging 9.8 ± 5.4 μ g N m −2 h −1 , −2.2 ± 0.9 μ g N m −2 h −1 , and 0.67 ± 0.57 μ g N m −2 h −1 in the low, mid, and high marshes, respectively. Both net N 2 O release and uptake were observed in the low and high marshes, but the mid‐marsh was consistently a net N 2 O sink. Gross N 2 O production was highest in the low marsh and lowest in the mid‐marsh ( P = 0.02), whereas gross N 2 O consumption did not differ among marsh zones. Thus, variability in gross N 2 O production rates drove the differences in net N 2 O flux among marsh zones. Our results suggest that future studies should focus on elucidating controls on the processes producing, rather than consuming, N 2 O in salt marshes to improve our predictions of changes in net N 2 O fluxes caused by future sea level rise.