[Distribution and Source Analysis of Nitrate in Surface Waters of China]

The nitrate pollution of surface water has attracted worldwide attention, and it is not optimistic in China. To identify the distribution, sources, and transformation mechanisms of nitrate in China's surface waters, the nitrate data of 71 major rivers from 7 regions were systematically collected. The spatial distribution of nitrate concentrations in surface water was analyzed, and the main nitrate pollution sources were revealed based on nitrogen and oxygen isotopes of nitrate. The results show that approximately 7.83% of rivers in China exceeded the Chinese drinking water standard for nitrate (45 mg·L^-1). The concentrations of nitrate in Mudanjiang, Haihe River, and the estuary of Yangtze River was even more than 90 mg·L^-1, which indicates a serious pollution phenomenon. The isotopic compositions of surface water in China ranged from -23.5‰ to 26.99‰ for δ¹⁵N-NO₃ and from -12.7‰ to 83.5‰ for δ¹⁸O-NO₃. The main sources of nitrate are domestic sewage in Northeast, Central, and East China, while those are inorganic fertilizers and domestic sewage in Southwest and South China. The nitrate sources of surface water in Northwest and North China are complex, mainly from domestic sewage, inorganic fertilizer, and nitration of soil organic matter. Through correlation analysis, it is found that the nitrate concentrations of surface water have a positive relationship with population, wastewater discharge, agricultural nitrogen fertilizer application, and GDP per capita in China. It is urgent to solve the problem of pollution and prevent the further pollution of China's surface waters. The new "10-Point Water Plan" issued by the Chinese government solved the previous problems, but it will take decades to control and repair the polluted surface waters. In Northwest, North China, Southwest, and South China, not only the scale of sewage treatment plants in cities and counties should be increased but also the use of agricultural fertilizers should be controlled and managed by the government. Northeast, Central, and East China need to further control point source pollution and reduce the discharge of industrial wastewater and domestic sewage into rivers.