Inorganic nitrogen wet deposition in eastern China: Comparison of different land use-based monitoring sites in north and south regions

Abstract

China is one of the global hotspots of atmospheric nitrogen (N) deposition. This is especially true for eastern China, an economically developed and densely populated area, which emits large quantities of anthropogenic reactive N species to the air and experiences high levels of atmospheric N deposition. Few studies, however, have examined spatial variations of N deposition across different ecosystems in northern and southern regions of eastern China. Using the traditional rain gauge (SDM6A) method, we conducted a three-year (2011-2013) study to quantify wet N deposition fluxes at twelve sites (six northern and six southern monitoring sites, covering urban, rural and background land use types) in China. The annual volume-weighted mean (VWM) concentrations of NH4+-N, NO3--N and total inorganic N (TIN) atmonitoring sites were in the ranges of 0.62-2.76, 0.54-2.50 and 1.25-4.92 mg N·L-1, and averaged 1.4, 1.5 and 2.9 mg N·L-1, respectively. Northern sites showed higher concentrations of N species in precipitation than southern sites. Annual deposition fluxes of NH4+-N, NO3--N and TIN were in the ranges of 7.0-18.3, 6.9-18.9 and 14.9-32.6 kg N·hm-2·a-1, averaging 11.5, 12.2 and 23.7 kg N·hm-2·a-1, respectively. There were significant differences in total N deposition fluxes among different land use types in the north, showing the decreasing order of urban sites (26.3±6.4 kg N·hm-2·a-1)> rural sites (21.8±3.5 kg N·hm-2·a-1)> background (15.5±1.3 kg N·hm-2·a-1). Total N deposition fluxes at urban, rural and background sites in the south were (26.8±2.7), (25.5±2.9) and (20.5±2.4) kg N·hm-2·a-1, respectively, showing no significant spatial variation. While urban sites did not show obvious regional differences, total N wet deposition fluxes at rural and background sites in the south were significantly higher than those at corresponding sites in the north. Our results revealed that both south and north regions of eastern China (including background areas) are receiving high levels of wet N deposition and associated ecological and environmental risks should be considered.