Spatiotemporal variations of nitrogen and phosphorus deposition across China

Atmospheric deposition is an important pathway for the input of anthropogenic and natural nutrients to terrestrial and aquatic ecosystems. However, previous measurements focused mainly on hotspot locations, ignoring the fact that the deposition magnitudes of various nutrient species (e.g., nitrogen (N), phosphorus (P)) at a national scale should be investigated jointly. To better characterize national scale bulk deposition, precipitation samples were collected at 41 sites across China from September 2015 to August 2016 and September 2017 to August 2018. The bulk deposition fluxes of total nitrogen (TN) and total phosphorus (TP) over the network were 27.5 kg N ha-1 yr-1 and 0.92 kg P ha-1 yr-1, respectively. Contributions of NH4+, NO3-, and dissolved organic nitrogen (DON) to TN averaged 32%, 32%, and 36%, respectively. Significant spatial and seasonal variations in concentrations and deposition fluxes of all nutrient species were observed reflecting effects of local reactive nitrogen (Nr) and P emissions and rainfall amount. Major sources were energy resource consumption for NO3-, agricultural activities for NH4+, and a mixed contribution of both anthropogenic and natural sources for DON and TP. Atmospheric N and P deposition represent important external nutrient inputs to ecosystems and a high ratio of TN to TP (29.9) may induce relative P-limitation and further increase the risk of eutrophication. This work reveals a new map of atmospheric N and P deposition and identifies regions where emissions should be controlled to mitigate long-term impacts of atmospheric deposition over China.