Effects of acid deposition control in China: a review based on responses of subtropical forests

Highlights

● S and N leaching from forest soils declined due to recent decreases in anthropogenic S and N emissions in China.

● Streamwater chemistry recovery was delayed by at least 5 years after peak S and N deposition.

● N₂O–N emission are particularly high in (sub)tropical forests and may amount to 8% of total N deposition from the atmosphere.

● N₂O emissions from forest soils declined with reduction in N deposition.

Abstract

For many decades, acid deposition used to pose a significant regional air pollution challenge in China. After substantial emission control of anthropogenically derived sulfur and nitrogen containing gasses, both sulfur and nitrogen deposition, as well as the acid rain-affected area, have significantly decreased compared to their peak levels. Forests, particularly in the humid subtropics, are sensitive to acid deposition, as evidenced by soil acidification, sulfate and nitrate leaching in stream water, and elevated soil nitrous oxide emission. Reduction in the total deposition of sulfur and nitrogen, caused a significant decline in sulfate and nitrate leaching from subtropical forest and subsequently in sulfate and nitrate concentrations in stream water, although there was about a 5-year delay. This delay may be attributed to the desorption of accumulated sulfate and continued elevated mineralization of accumulated nitrogen pools. Emissions of nitrous oxide, a potent greenhouse gas, also declined in nitrogen-saturated subtropical forest soils, as soil water nitrate concentration decreased. Therefore, subtropical forests in China suffering from elevated acid deposition have begun to recover. Yet, the current levels of sulfur and nitrogen deposition continue to exceed the critical loads, i.e., the assigned threshold levels in accordance with emission control policies, in more than 10% of the country’s land area, respectively, indicating remaining risks of acidification and eutrophication. Thus, further emission reductions are urgently needed, also because they will help achieving goals related to air quality and nitrous oxide emissions.

Keywords

Acidification / Critical load / Nitrous oxide / Surface water chemistry / Recovery

Lei Duan is a Professor in the School of Environment at Tsinghua University. He received a B.S. and a Ph.D. from Tsinghua University, both in Environmental Engineering. He joined Tsinghua University as a lecturer in 2000, then promoted to an associated professor in 2003. In 2010 he became a full professor. His research interests include the effects of air pollution on ecosystem, emission characteristics of air pollutants, and biogeochemical processes of sulfur, nitrogen, and mercury in terrestrial ecosystems. He has published over 230 journal papers, which have been cited for more than 11,500 times with an H-index of 50 (WOS). He has received 2 National Science and Technology Progress Awards of China. He was the member of Scientific Program Committee of the 8th–10th International Acid Rain Conference

Jan Mulder is a Professor in Soil Science and Biogeochemistry at the Department of Environmental Sciences and Natural Resource Management (MINA), Norwegian University of Life Sciences (NMBU). He is a soil chemist by training, with a Ph.D. degree from Wageningen University (The Netherlands). His Ph.D. focused on acid rain, soil acidification and the mobility of soil aluminum. After that he has worked primarily on the biogeochemistry of carbon, nitrogen and metals in terrestrial ecosystems, including forests, grasslands and agro-ecosysems. Most recently dr. Mulder focused on N₂O research in nitrogen-saturated forests of Southwest China and on the potential of biochar in climate change mitigation and adaptation of smallholder agriculture in sub-Saharan Africa. Professor Mulder is member of the Norwegian Academy of Science and appointed Distinguished Visiting Professor at the School of Environment, Tsinghua University. He has about 175 peer reviewed publications (ISI Web of Science) and an H-index of 53. He has been associate editor of Biogeochemistry and of the European Journal of Soil Science

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Acknowledgements

The authors are grateful for the financial support from the National Key Research and Development Project (No. 2022YFC3700600), the National Natural Science Foundation of China (Nos. 42303061 and 42277204), the Norwegian Directorate for Higher Education and Skills (HK-DIR, projects UTF-2016-long-term/10089 and UTF-2020/10180), and the Young Talent Fund of Association for Science and Technology in Shaanxi, China (20230704).

Conflict of Interests

Jan Mulder is an editorial board member of Frontiers of Environmental Science & Engineering. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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