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Anthropogenic emissions of nitrogen- (N) and sulfur (S)-containing pollutants have declined across China in recent years. However, the responses of N and S depositions and dynamics in soil remain unclear in subtropical forests. In this study, the wet and throughfall depositions of dissolved inorganic N (DIN) and SO42− were continuously monitored in a mildly polluted subtropical forest in Southeast China in 2017 and 2018. Moreover, these solutes in soil water along the soil profile were monitored in 2018. Throughfall deposition of DIN and S decreased by 59% and 53% in recent 3 years, respectively, which can be majorly attributed to the decreases in wet depositions of NO3− and SO42−. Meanwhile, NH4+ deposition remained relatively stable at this site. Even though N deposition in 2018 was below the N saturation threshold for subtropical forests, significant N leaching still occurred. Excess export of N occurred in the upper soil layer (0–15 cm), reaching 6.86 ± 1.54 kg N/ha/yr, while the deeper soil (15–30 cm) was net sink of N as 8.29 ± 1.71 kg N/ha/yr. Similarly, S was excessively exported from the upper soil with net flux of 14.7 ± 3.15 kg S/ha/yr, while up to 6.37 ± 3.18 kg S/ha/yr of S was retained in the deeper soil. The significant N and S leaching under declined depositions suggested that this site possibly underwent a transition state, recovering from historically high acid deposition. Furthermore, the rainfall intensity remarkably regulated leaching and retention of SO42− and DIN at this site. The impacts of climate changes on N and S dynamics require further long-term monitoring in subtropical forests. [ABSTRACT FROM AUTHOR]

Acidic deposition used to cause severe surface water acidification in Europe and the North America, but no damage of surface water acidification was reported under continuous heavy acid deposition in China. We present the first detailed study on regional surface water acidification in southern and northeastern China based on a survey of 255 forested headwater streams, which were investigated during 2010–2015 to explore the status and mechanism of surface water acidification. South China has a subtropical climate with high acid deposition, whereas northeast China is located in a cold temperature zone with relatively low acid deposition. High pH and acid neutralizing capacity (ANC) were observed for almost all of the streams, indicating that surface water acidification may not be a serious regional issue in China both at present and in the future. In northeast China, where soil types are similar in low weathering rate to those in Northern Europe and North America, the ANC of surface waters was lower than that in South China, indicating a higher acid-sensitivity of the surface water. In comparison, the high pH and ANC of streams in southwest China resulted from high soil weathering and atmospheric calcium (Ca) deposition, despite elevated atmospheric acid inputs due to the high sulfur (S) and nitrogen (N) deposition. Comparison of stream nitrate (NO 3 − ) and sulfate (SO 4 2 − ) concentrations with modeled N and S deposition showed significant N and possible S sinks in the catchments in south China, probably due to denitrification of NO 3 − in groundwater discharge zone and SO 4 2 − adsorption by acid soils respectively, which may also buffer the acidifying effect of S and N depositions. It seems that considerable NO 3 − leaching to stream waters does not occur in China unless N deposition is higher than 1.8 keq·ha − 1 ·yr − 1 (2.50 g N·m − 2 ·yr − 1 ) (or greater values in certain regions). [ABSTRACT FROM AUTHOR]