Wet deposition and sources of inorganic nitrogen in the Three Gorges Reservoir Region, China.

Abstract

Precipitation samples were collected at five rural and one urban sites in the Three Gorges Reservoir Region (TGR), China from March 2014 to February 2016. The inorganic reactive nitrogen (Nr) contents were analysed to investigate their wet deposition flux, budget, and sources in the area. Annual Nr wet deposition varied from 7.1 to 23.4kgN ha-1 yr-1 over the six sites during the two-year study campaign. The six-site average Nr wet deposition flux was 17.1 and 11.7kgN ha-1 yr-1 in 2014 and 2015, respectively, with 71% from NH4+ and 29% from NO3-. Dry deposition flux was estimated using the inferential method, which combined the measured ambient concentrations and modelled dry deposition velocities. The total (dry+wet) Nr deposition fluxes were estimated to be 21.4kgN ha-1 yr-1 in 2014 and 16.0kgN ha-1 yr-1 in 2015at rural sites, and 31.4 and 25.3kgN ha-1 yr-1 at the urban site. Annual average volume weighted mean (VWM) concentrations in precipitation at all the six sites differed little for NO3- but up to a factor of 2.0 for NH4+ with the highest value at the urban site. Industrial emissions, agricultural emissions, soil dust, and biomass burning were identified as potential sources of the major inorganic ions in precipitation using factor analysis and correlation analysis. Conditional probability function (CPF) analysis indicated that the urban site was predominantly affected by industrial emissions from a power plant, cement manufactory, and salt chemical facility located ∼13km southeast of the sampling site.