Drivers, trends and impacts of nitrogen deposition in China

Abstract

Since 1980, there have been substantial changes in reactive nitrogen (Nr) deposition in China, with implications for nutrient pollution, ecosystem health and the sustainability of food systems. This Review synthesizes evidence from national monitoring networks and modelling studies to elucidate the drivers and profound ecological consequences of these changes. Nr deposition increased to a maximum of 16.4 Tg N yr−1 in 2010–2012. Thereafter, stringent industrial nitrogen oxide (NOx) emission controls led to a 14% decline in total Nr deposition by 2020, to 13.3 Tg N yr−1, primarily through a 34% reduction in oxidized nitrogen. Reduced nitrogen from agriculture now dominates Nr deposition, constituting 60–70% of the total deposition. This dominance of reduced nitrogen has resulted in severe ecological impacts, including widespread soil acidification, freshwater eutrophication and biodiversity loss. As of 2020, ~15% of China’s land area is experiencing Nr deposition exceeding critical loads for eutrophication. Future climate change, particularly warming and intensified precipitation extremes, is projected to further reduce ecosystem resilience, thereby increasing the terrestrial area in which Nr deposition exceeds critical loads for eutrophication. China would need to achieve reductions in ammonia and NOx deposition of 56–76% and 53–60%, respectively, to match average Nr deposition levels in the USA and Western Europe. Thus, integrating agricultural ammonia management into wider climate and air quality policies is a priority to ensure ecosystem protection and long-term environmental sustainability in China. Reactive nitrogen deposition in China has changed markedly since 1980 owing to variations in emissions from industry and agriculture, with consequences for ecosystems, food systems and pollution control. This Review synthesizes deposition trends, emission and meteorological drivers, ecological impacts and management strategies for sustainable nitrogen mitigation in China.