Study On The Characteristics And Simulation Of Non-point Source Pollution In The Jinyunchuan River Basin

It has been realized that non-point source pollution is one of the most important causes of water pollution.Research on non-point source pollution in river basins plays a significant role in the improvement and protection of water environment.Jinyunchuan river is one of the most important rivers in Jinan City.After converging with Jinyangchuan river,Jinyunchuan river flows into Wohushan Reservoir,an important water source in Jinan.Therefore,the water quality of Jinyunchuan river directly affects the safety of drinking water in Jinan City.Taking Jinyunchuan basin as the study area,coefficient estimation method was used to estimate the non-point source pollution load of the basin,and the current water quality situation was analyzed and evaluated based on collecting water samples in the Jinyunchuan basin.Then the SWAT model was constructed and carried out parameter sensitivity analysis,model calibration and verification,and identified the critical source areas of non-point source pollution in the study area.The main findings are as follows:（1）Estimation of non-point source pollution load in the watershed.The coefficient method is used to estimate the pollution load generated by different non-point source pollution sources,including planting pollution,livestock and poultry breeding pollution,and rural domestic pollution.In 2021,the amount of TN and TP loss from planting pollution in Jinyunchuan river basin was 82.21 t and 20.35 t,and the total amount of pesticide and agricultural film used was 28537.03 kg.The amount of COD,TN,TP,and NH₃-N loss from livestock and poultry breeding pollution was 2.55 t,0.67 t,0.22 t,0.23 t.The amount of COD,TN,TP,and NH₃-N loss from rural domestic pollution was 84.41 t,9.75 t,2.29 t,3.54 t.（2）Analysis and evaluation of water quality.The monitoring and analysis of the Jinyunchuan river basin water quality 2021 from July to July 2022 showed that the water body was weakly alkaline.The indicators of DO,COD,NH₃-N were relatively good,while the indicator of TN was relatively poor.Some of the water quality indicators showed obvious seasonal changes in time distribution.The spatial distribution of lake water quality has little difference among seasons.From the perspective of spatial scale,most water quality indicators had small seasonal spatial distribution differences except for COD.TN was the main pollution factor affecting water quality.（3）Modeling and simulation of non-point source pollution.SWAT model was used to simulate non-point source pollution in the Jinyunchuan river basin.The results showed that the regular and validation periods of runoff rate were R²=0.91 and 0.88,while E_ns=0.88 and0.84.The regular and validation periods of TN rate were R²=0.82 and 0.84,while E_ns=0.76and 0.74.The regular and validation periods of TP rate were R²=0.85 and 0.82,while E_ns=0.82 and 0.78.（4）Analysis of the characteristics of non-point source pollution and identification of critical source areas in Jinyunchuan river basin.On the time scale,there were significant seasonal differences in nitrogen and phosphorus pollution loads,which were positively correlated with rainfall.The overall distribution trend of TN and TP loss intensity was higher in the north and south,while lower in the middle.Using the loss intensity index method to identify the key source areas of non-point source pollution in the study area,determining the critical source areas of non-point source pollution is the sub basins of 2,5,7,and 17,which account for 28.39%of the entire study area,the contribution rate of TN and TP load exceeds50%.Therefore,these sub basins were the main areas where nitrogen and phosphorus pollution loads were generated.