Characteristics Of Non-point Source Pollution Load And Its Influence On Water Quality In Ciyao River Basin

During the 13 th Five-Year Plan period,the prevention and control of water pollution in Shanxi Province has achieved remarkable results,and the quality of river water environment has improved significantly.While the point source pollution has been effectively controlled,the problem of non-point source pollution in the basin has become prominent and received more attention.In this paper,the Ciyao River,the first tributary of Fenhe River in Shanxi Province,is taken as the research object.In order to solve the problem of water environmental pollution in the basin,the PLOAD model is used to study the load quantification of non-point source pollution in the basin,and the critical source areas and key pollution sources of non-point source pollution are identified.Combined with the water quality monitoring data of the basin,the reasons for the change of water quality index pollution concentration in different periods of the basin are analyzed,and the characteristics of water quality pollution in the region are identified.The best management measures of non-point source pollution(BMPs)are introduced.The environmental benefits of various measures are evaluated by PLOAD model.Targeted control strategies are proposed for the prevention and control of water environmental pollution in the region.(1)The digital elevation model,land use type,average concentration of runoff pollutants(EMC)and other data of Ciyao River Basin were collected to construct the PLOAD model of non-point source pollution.According to the surface coating and terrain characteristics,the quantitative analysis of non-point source pollution load of key indicators of water quality pollution in the basin was carried out in different regions,and the critical source areas and key pollution sources of non-point source pollution were identified.The results showed that the non-point source pollution load of Ciyao River Basin was 667.72 t/a for total nitrogen,235.42t/a for ammonia nitrogen,103.54 t/a for total phosphorus,and 8839.37 t/a for chemical oxygen demand.The pollution load intensity was total nitrogen 0.623 t/(km2·a),ammonia nitrogen0.220 t/(km2·a),total phosphorus 0.097 t/(km2·a),chemical oxygen demand 8.253 t/(km2·a).The critical source areas of non-point source pollution are mainly distributed in the middle reaches of urban areas where 12 #,13 #,16 #,24 # sub-basins are located and downstream agricultural areas where 27 #,28 #,30 #,32 # sub-basins are dominated.Cultivated land and urban land are the main land types for pollutant output in the basin.(2)In the non-flood season and flood season,the water quality of Ciyao River Basin was sampled and analyzed.The basic water quality index analysis,nitrogen index analysis,phosphorus distribution analysis,chemical oxygen demand index analysis,heavy metal pollution distribution analysis and soil status analysis of the basin were carried out.Combined with the EMC value of the model output,the reasons for the differences in water quality in different periods were analyzed.The results showed that the pollution of each index in Ciyao River Basin was different.The pollution of total nitrogen and nitrate nitrogen in non-flood season was heavier,but the pollution in flood season was weakened.The pollution of ammonia nitrogen,total phosphorus and chemical oxygen demand in non-flood season is relatively light,but the pollution in flood season is aggravated.(3)The scenario analysis method was used to analyze the BMPs of non-point source pollution.Taking the critical source areas identified in the basin as the research area,different BMPs scenarios were analyzed,and the PLOAD model was used to evaluate the environmental benefits under different measures scenarios.The results showed that the best reduction effect of total nitrogen,ammonia nitrogen and total phosphorus pollution was farmland fertilization management measures,and the reduction rates were 12.41%,11.28% and 10.36%,respectively,indicating that controlling agricultural non-point source pollution in the basin can effectively control the loss of nitrogen and phosphorus.The management measures of human and animal feces have the best effect on the reduction of COD pollution,with the reduction rate of 12.68%,indicating that the reduction of COD should focus on the pollution control in urban and rural areas.