Non-point Source Pollution Characteristic Analysis Of DuLiuJianhe River Basin In XiQing Based On SWAT Model

In recent years,the economic level of the Duliujianhe River Basin has developed rapidly,the process of urbanization has accelerated,and water pollution has become more and more serious.With the basic control of point source pollution,non-point source pollution has gradually become the main cause of water environmental pollution in the river basin.This study takes the Duliujianhe River Basin in Xiqing with poor water quality as the research object.The non-point source pollution load model is established by collecting DEM data,land use data,soil type data,meteorological data,hydrological and water quality data,and agricultural management measures in the basin to estimate the non-point pollution inflow load from 2016 to 2020,in order to provide an important scientific basis for the prevention and control of non-point source pollution in the Duliujianhe River Basin in Xiqing and the ecological environment protection of river water.According to the research results of this article,the following conclusions are obtained:（1）This article uses Cite Space and VOSviewer bibliometric software,with"non-point source pollution"and its synonyms as keywords,carries out a bibliometric analysis of relevant domestic and foreign literature,focusing on the non-point pollution load models,especially the development process,applicable watersheds,simulable content and research hotspots of the SWAT model have been sorted out and analyzed,and the research focus of this article has been determined-exploring the impact of land use data spatiotemporal changes on non-point source pollution in watersheds.（2）Based on the collected spatial and attribute data of the research basin,a non-point pollution load model for the Duliujianhe River Basin in Xiqing is constructed.The model was calibrated and validated by using the 2016-2020 measured data from the basin outlet to ensure its performance.The resolvable coefficient R²,Nash coefficient E_NS and relative error|RE|were used as model evaluation indicators.The output results show that the runoff rates of R²and E_NS are greater than 0.8 and relative error|RE|<15%during the calibration and verification periods;the R² and E_NSof ammonia nitrogen and total phosphorus are greater than 0.7 and relative error|RE|<30%during the calibration and verification periods.In summary,the SWAT model has a good simulation effect on the runoff and water quality of the research basin,and its output results can provide a basis for subsequent research and analysis.（3）The output of the model shows that in terms of time distribution,the annual average inflow loads of organic nitrogen,nitrate nitrogen,nitrite nitrogen,ammonium nitrogen,organic phosphorus and mineral phosphorus in Duliujianhe River Basin in Xiqing from 2016 to 2020 were 338.7t,11.05t,7.55t,163.3t,47.35t and 99.13t respectively;the output of pollution loads were positively correlated with precipitation,and them production and discharge were mainly concentrated in June to October.In terms of spatial distribution,pollutions were mainly concentrated on urban land in the northeastern part of the study basin.The total nitrogen loss per unit area is5.577-8.341 kg/ha,and the total phosphorus is 3.908-5.188 kg/ha.（4）It can be seen that agricultural land and urban land（including rural residential areas）have a greater contribution to the total amount of nitrogen and phosphorus pollution into the river,of which urban land（high density）was the largest,the contribution to organic nitrogen,nitrate nitrogen,organic phosphorus,particulate inorganic phosphorus and soluble inorganic phosphorus accounted for 61.66%,68.69%,58.29%,64.19%and 52.14%respectively.This paper extracts the four phases of land use data in 2000,2005,2010 and 2018,and they were set up to simulate and analyze the non-point pollution in the study basin.The results show that with the continuous increase of urban land area,the non-point pollution loads were also showing an increasing trend.Compared with the 2000 land use scenario,the load of organic nitrogen in the 2018 land use scenario increased by 66%,the organic phosphorus increased by 153%,the ammonium nitrogen increased by 137%,and mineral phosphorus increased by 61%.And they have also affected the spatial distribution of non-point nitrogen and phosphorus pollution.From 2000 to 2018,urban land gradually replaced agricultural land as the main source of non-point source pollution.The newly expanded urban land pollution is very prominent,the area of moderate to severe pollution has gradually increased.In this paper,the sub-catchments 3-6,21,and 30 with the highest nitrogen and phosphorus pollution load are designated as the key source areas of the study area,and the urban land types in the key source areas are changed to woodland,grassland and low-density residential areas,respectively.Bringing the land use data under the above three scenarios back to the model,the output results show that the non-point pollution loads under the three scenarios have been reduced,and the reduction effect is:woodland>grassland>low-density residential area.（5）This paper proposes a pollution control project for aquaculture polluti—constructed wetland construction.After literature review and field investigation,suitable artificial wetland restoration technologies and wetland plants were selected to return fishing to wetland on part of fish ponds to reduce the non-point pollution loads in the study basin.