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

Many estuaries experience eutrophication, deoxygenation and warming, with potential impacts on greenhouse gas emissions. However, the response of NO production to these changes is poorly constrained. Here we applied nitrogen isotope tracer incubations to measure NO production under experimentally manipulated changes in oxygen and temperature in the Chesapeake Bay-the largest estuary in the United States. NO production more than doubled from nitrification and increased exponentially from denitrification when O was decreased from >20 to <5 micromolar. Raising temperature from 15° to 35°C increased NO production 2- to 10-fold. Developing a biogeochemical model by incorporating these responses, NO emissions from the Chesapeake Bay were estimated to decrease from 157 to 140 Mg N year from 1986 to 2016 and further to 124 Mg N year in 2050. Although deoxygenation and warming stimulate NO production, the modeled decrease in NO emissions, attributed to decreased nutrient inputs, indicates the importance of nutrient management in curbing greenhouse gas emissions, potentially mitigating climate change.