Using SWAP to Study the Changes in Nonpoint Source Pollution in Burhatong River Basin

Abstract

【Background】 Nonpoint source pollution can cause eutrophication and biodiversity loss in rivers and lakes. In China, nonpoint source pollution from agriculture has become an environmental concern and understanding its composition and spatial distribution in watershed is essential to improving its management and mitigating its detrimental impact. 【Objective】 The purpose of this paper is to study the impact of land usage on spatiotemporal change in nonpoint source pollution, and elucidate its relationship with watershed landscape. 【Method】 We took the Burhatong river basin as an example and used the distributed hydrological model SWAT to simulate dynamics of nonpoint source pollution induced by four land use changes from 1986 to 2016. The Fragstats 4.2 software was used to calculate the landscape pattern index of the sub-basins, and its relationship with nonpoint source pollution was analyzed using the CANOCO5.0 software. 【Result】 ①The determination coefficient and the Nash efficiency coefficient of the runoff and total phosphorus amount simulated by the SWAT in calibration and verification were all higher than 0.6. The model can thus be used to simulate water quality in the watershed. For the four land usage changes from1986 to 2016, the total annual phosphorus load simulated by the model was 74.04, 73.78, 82.50 and 128.31 tons, respectively. ②There is a close relationship between nonpoint source pollution and landscape pattern. In terms of landscape composition pattern, the total phosphorus load was negatively correlated to forest land, while positively correlated to farmland and construction land. In terms of landscape spatial pattern, the total phosphorus was positively correlated to fragmentation of forest land, while negatively correlated to fragmentation of farmland. Increasing materials flow between patches and enhancing patch aggregation can reduce nutrient loss, while increasing landscape heterogeneity and complexity increases pollution risk. 【Conclusion】 Nonpoint source pollution in the watershed of Burhatong basin has increased steadily, especially in the slopped areas in the north and agricultural and urban areas in the east. Reducing forest land fragmentation and controlling urban nonpoint source pollution can help mitigate its detrimental impact.

Keywords

• swap
• non-point source pollution
• total phosphorus
• redundancy analysis