Total phosphorus has become the primary pollutant in the Yangtze River basin. For the Yangtze River basin, total phosphorus pollution mainly comes from nonpoint source pollution, sewage treatment facility discharge, soil erosion, etc.

What is nonpoint source pollution? Nonpoint source pollution generally results from land runoff, precipitation, atmospheric deposition, drainage, seepage or hydrologic modification. It means that under the condition of rainfall, pollutants are washed by rain through the runoff process and sink into rivers, lakes, reservoirs and bays, etc., causing water pollution.

Nonpoint source water pollution may derive from many different sources with no specific solutions or changes to rectify the problem, making it difficult to regulate.

Urban and suburban areas are the main sources of nonpoint source pollution. The runoff washes sediment from roads in logged forest areas. It can also carry acid from abandoned mines and wash away pesticides and fertilizers from agricultural fields. Agricultural nonpoint source pollution can contaminate the soil and reduce the quality of agricultural products. Also, it can cause harm to water bodies and the atmosphere.

Urban road surfaces, such as asphalt and concrete, are waterproof. Any water that comes in contact with these surfaces is lost and absorbed by the surrounding environment. These surfaces make it easier for rainwater to carry pollutants into the surrounding soil.

To minimize the discharge of nonpoint source pollution, lay permeable tiles or permeable ground, increase the area of green space and vegetation cover, treat initial rainwater, etc. Develop targeted regulations for nonpoint source pollution, such as control of fertilizer and pesticide on farmland, and regulations for organic waste emission control and recycling, Peng Jianfeng, Professor of School of Environment, Tsinghua University, said.

Editor：Guo Lili