Bulk phosphorous deposition at four typical land use sites in Southwest China

Whilst ongoing increases in the deposition of atmospheric nitrogen (N) in China have attracted a lot of attention, to date there has been little research on phosphorus (P) deposition. In this study, we quantified inorganic P (PO₄^3-), dissolved organic P (DOP) and total P (TP) in bulk deposition at four sites in the Sichuan Basin, Southwest China. Chengdu (CD), Shifang (SF), Yanting (YT), and Gongga (GG). They represent the land use categories urban, suburban, agricultural and forest, respectively, during 2008-2018 at CD and YT, 2015-2018 at SF, and 2007-2014 at GG. Annual average TP concentrations (deposition rates) were 0.07 (0.61), 0.49 (3.22), 0.17 (1.07) and 0.01 (0.20) mg L^-1 (kg ha^-1 yr^-1), at CD, SF, YT and GG, respectively. The TP concentrations at YT and GG showed significant increasing trends over the years, with very little change at CD and a decline at SF because of the implementation of environmental control measures. Average PO₄^3- to DOP ratios were 0.65, 0.95, 0.82 and 0.81 at CD, SF, YT and GG, respectively, indicating that DOP accounts for a higher proportion at the urban site, and dominated by combustion sources. Bulk P deposition showed higher deposition rates in summer and lower in winter. These results highlight the importance of long term monitoring in detecting spatial and temporal changing trends of the chemical composition, so as to implement effective policies to eliminate air pollution, especially for Southwest China, where there is limited research on atmospheric P deposition.