The three largest acid rain regions are Europe, North-America, and East Asia (especially subtropical China). Due to different natural and environmental conditions, surface water acidification was less severe in China than in Europe and North-America, although the water chemistry still changed considerably. When the emissions of sulfur and nitrogen started to decrease in China, the recovery of acidified surface waters was expected. The headwater stream sulfate and nitrate concentrations decreased. The decline rate of sulfur leaching in subtropical forest region was higher than that in temperate forest region, indicated the recovery was more rapid in subtropical forest region. However, the subtropical forest region retained largely sulfur under high sulfur deposition. The release of previously deposited sulfur stored in soil, delaying the recovery of the surface water chemistry, whereas the effect lasted at least 5 years. After the sulfur deposition declined from the peak value, the net sulfur release ratio remained high in 2010 even in the subregion of purplish soil with low sulfate adsorption capacity, and it had declined to zero until 2018. Meanwhile, the subregion of red and yellow soil with high sulfate adsorption capacity was sulfur sink all along, indicating that the sulfate reduction was still existed although the sulfur deposition declined, and counteracted the sulfate desorption. For nitrogen, there was a large sink in the catchment, retained approximately 80% of deposited nitrogen in the Sichuan Basin. The nitrogen leaching decreased slowly with the nitrogen deposition declined, except at the region where nitrogen deposition exceeds the critical threshold.

Surface water; Sulfur sink; Nitrogen sink; Acidification; Acid deposition; Emission abatement