Load quantification and effect evaluation of urban non-point source pollution in the Licun River based on SWAT model

With the gradual control of point source pollution, the impact of urban nonpoint source pollution on river water quality is becoming more prominent. Regarding the current problem that nonpoint source pollution loads in urban basins are difficult to quantify and the impact on water quality is difficult to analyze, the Licun River basin in Qingdao was selected as the research object. Through the field survey and surface accumulation sampling analysis of the basin, the evaluation model of urban nonpoint source pollution was constructed by revising the land type data of the basin and the urban database of the SWAT model. The results showed that concentration of nitrate in precipitation was most sensitive to the simulation of nitrogen loading; organic P in baseflow was most sensitive to the simulation of phosphorus loading. The Nash- Sutcliffe efficiency coefficient (E-NS) and the coefficients of determination (R-2) of the SWAT model for runoff, TP, and TN in the simulation validation period meet the model requirements,indicating a good model fit. In addition, the spatial and temporal distribution characteristics of urban nonpoint source pollution of TN and TP in 2021 were analyzed. In July, rainfall-runoff from the Licun River basin was the most polluted.

Automated summary

By conducting field surveys and surface accumulation sampling analysis in the Licun River basin in Qingdao, the evaluation model of urban nonpoint source pollution was constructed by revising the land type data and the urban database of the SWAT model. The results showed that nitrate concentration in precipitation was most sensitive to nitrogen loading simulation, and organic P in baseflow was most sensitive to phosphorus loading simulation. The model fit was good, meeting the requirements for runoff, TP, and TN. Additionally, the spatial and temporal distribution characteristics of urban nonpoint source pollution of TN and TP in 2021 were analyzed, with the most polluted month being July in the Licun River basin.