Nutrient management offsets the effect of deoxygenation and warming on nitrous oxide emissions in a large US estuary

Abstract

Many estuaries experience eutrophication, deoxygenation and warming, with potential impacts on greenhouse gas emissions. However, the response of N 2 O production to these changes is poorly constrained. Here we applied nitrogen isotope tracer incubations to measure N 2 O production under experimentally manipulated changes in oxygen and temperature in the Chesapeake Bay—the largest estuary in the United States. N 2 O production more than doubled from nitrification and increased exponentially from denitrification when O 2 was decreased from >20 to <5 micromolar. Raising temperature from 15° to 35°C increased N 2 O production 2- to 10-fold. Developing a biogeochemical model by incorporating these responses, N 2 O emissions from the Chesapeake Bay were estimated to decrease from 157 to 140 Mg N year −1 from 1986 to 2016 and further to 124 Mg N year −1 in 2050. Although deoxygenation and warming stimulate N 2 O production, the modeled decrease in N 2 O emissions, attributed to decreased nutrient inputs, indicates the importance of nutrient management in curbing greenhouse gas emissions, potentially mitigating climate change.