Atmospheric wet deposition of sulfur and nitrogen in Jiuzhaigou National Nature Reserve, Sichuan Province, China

In the last two decades, remarkable ecological changes have been observed in Jiuzhaigou National Nature Reserve (JNNR). Some of these changes might be related to excessive deposition of sulfur (S) and nitrogen (N), but the relationship has not been quantified due to lack of monitoring data, particularly S and N deposition data. In this study, we investigated the concentrations, fluxes, and sources of S and N wet deposition in JNNR from April 2010 to May 2011. The results show that SO₄^2-, NO₃^-, and NH₄⁺ concentrations in the wet deposition were 39.4-170.5, 6.2-34.8, and 0.2-61.2μeqL^-1, with annual Volume-Weighted Mean (VWM) concentrations of 70.5, 12.7, and 13.4μeqL^-1, respectively. Annual wet deposition fluxes of SO₄^2-, NO₃^-, and NH₄⁺ were 8.06, 1.29, and 1.39kgS(N)ha^-1, respectively, accounting for about 90% of annual atmospheric inputs of these species at the monitoring site. The results of Positive Matrix Factorization (PMF) analysis show that fossil fuel combustion, agriculture, and aged sea salt contributed to 99% and 83% of annual wet deposition fluxes of SO₄^2- and NO₃^-, respectively. Agriculture alone contributed to 89% of annual wet deposition flux of NH₄⁺. Although wet deposition in JNNR was polluted by anthropogenic acids, the acidity was largely neutralized by the Ca²⁺ from crust and 81% of wet deposition samples had a pH higher than 6.00. However, acid rain mainly caused by SO₄^2- continued to occur in the wet season, when ambient alkaline dust concentration was lower. Since anthropogenic emissions have elevated S and N deposition and caused acid rain in JNNR, further studies are needed to better quantify the regional sources and ecological effects of S and N deposition for JNNR.