Nitrogen emission and deposition budget in an agricultural catchment in subtropical central China.

The study of emissions and depositions of atmospheric reactive nitrogen species (Ns) in a region is important to uncover the sources and sinks of atmospheric Ns in the region. In this study, atmospheric total Ns depositions including both wet-only and dry deposition were monitored simultaneously across major land-use types in a 105 km catchment called Jinjing River Catchment (JRC) in subtropical central China from 2015 to 2016. Based on activity data and emission factors for the main Ns emission sources, ammonia (NH) and nitrogen oxides (NO) emission inventories for the catchment were also compiled. The estimated total Ns deposition in JRC was 35.9 kg N ha yr, with approximately 49.7 % attributed to reduced compounds (NH), and 40.5 % attributed to oxidized (NO). The total Ns emission rate in JRC was 80.4 kg N ha yr, with 61.5 and 18.9 kg N ha yr from NH and NO emissions, respectively. Livestock excretion and fertilization were the two main contributing emission sources for NH, while vehicle sources contributed the bulk of NO emissions. The net atmospheric budgets of Ns in paddy field, forest, and tea field were +3.7, -36.1, and +23.8 kg N ha yr, respectively. At the catchment scale, the net atmospheric budget of Ns was +47.7 kg N ha yr, with +43.7 kg N ha yr of NH and +4.0 kg N ha yr of NO indicating that the subtropical catchment was net sources of atmospheric Ns. Considering that excessive atmospheric N emissions and deposition may cause adverse effects on the environment, effects should be conducted to mitigate the Ns emissions from agriculture and transportation, and increasing the area of forest is good for reducing the net positive budget of atmospheric Ns in the subtropical catchments in China.