Climate factors affect N2O emissions by influencing the migration and transformation of nonpoint source nitrogen in an agricultural watershed

Precipitation can affect the residence time of nitrogen compounds, and temperature can influence nitrogen transformation in soil. Therefore, we hypothesized that climate factors can affect the emissions of N2O, an important greenhouse gas produced via nitrogen transformation, by influencing the migration and transformation of nonpoint source nitrogen in soil. To test this hypothesis and quantify the effect of climate factors on N2O emissions, the SWAT model and the modified SWAT-N2O coupler were used to study the effect of climate factors on the migration and transformation of nonpoint source nitrogen and N2O emissions in an agricultural watershed from 2009 to 2018. Temperature affected N2O emissions more significant than precipitation, and N2O emissions increased with temperature and reached a plateau when the average monthly temperature was 23.0 degrees C. The N2O emissions first increased rapidly with precipitation due to the increase in moisture. However, when the average monthly precipitation reached 78.8 mm, the N2O emissions began to decrease because the residence time of nitrogen compounds in soil were reduced due to fast removal via runoff, which inhibits N2O emissions. Under the context of climate change with three scenarios (RCP2.6, RCP4.5, RCP8.5), temperature would increase gradually while precipitation would not change significantly from 2021 to 2080, as a result, the changes would increase N2O emissions by 6.7%, 32.3%, and 70.7%, respectively. This study quantifies the feedback of N2O emissions to climate change in croplands, providing a scientific basis for climate change mitigation and agricultural management.

Automated summary

This study used the SWAT model and modified SWAT-N2O coupler to investigate the impact of climate factors on the migration, transformation, and emissions of nonpoint source nitrogen and N2O in an agricultural watershed. The findings show that temperature has a more significant effect on N2O emissions compared to precipitation, with N2O emissions increasing with temperature. Additionally, precipitation initially enhances N2O emissions due to increased moisture, but emissions decrease when precipitation exceeds a certain threshold. Under different climate change scenarios, increasing temperatures will lead to a rise in N2O emissions.