Enhanced nitrogen deposition over China

摘要

China is experiencing intense air pollution caused in large part by anthropogenic emissions of reactive nitrogen. These emissions result in the deposition of atmospheric nitrogen (N) in terrestrial and aquatic ecosystems, with implications for human and ecosystem health, greenhouse gas balances and biological diversity. However, information on the magnitude and environmental impact of N deposition in China is limited. Here we use nationwide data sets on bulk N deposition, plant foliar N and crop N uptake (from long-term unfertilized soils) to evaluate N deposition dynamics and their effect on ecosystems across China between 1980 and 2010. We find that the average annual bulk deposition of N increased by approximately 8 kilograms of nitrogen per hectare (P< 0.001) between the 1980s (13.2 kilograms of nitrogen per hectare) and the 2000s (21.1 kilograms of nitrogen per hectare). Nitrogen deposition rates in the industrialized and agriculturally intensified regions of China are as high as the peak levels of deposition in northwestern Europe in the 1980s~6, before the introduction of mitigation measures. Nitrogen from ammonium (NH_4~+) is the dominant form of N in bulk deposition, but the rate of increase is largest for deposition of N from nitrate (NO_3~-), in agreement with decreased ratios of NH_3 to NO_x.emissions since 1980. We also find that the impact of N deposition on Chinese ecosystems includes significantly increased plant foliar N concentrations in natural and semi-natural (that is, non-agricultural) ecosystems and increased crop N uptake from long-term-unfertilized croplands. China and other economies are facing a continuing challenge to reduce emissions of reactive nitrogen, N deposition and their negative effects on human health and the environment.%大气氮排放自工业革命以来已有实质性增加，由此所造成的氮沉积对人类和生态系统健康会产生有害影响。但我们对当今发展最快的经济体中国的氮沉降的严重程度和环境后果却知之甚少。这篇论文报告，氮的年平均大体积沉积从上个世纪80年代到21世纪前十年增加了每公顷8公斤氮。在大体积沉积中，氦的主要形式为铵，而硝酸盐沉积的增长速度最大。氮沉积也增加了半自然生态系统中植物叶子的氮浓度，导致长期没有施肥的农田中作物氮吸收量升高。