Quantification of Effects of Natural Geographical Factors and Landscape Patterns on Non-point Source Pollution in Watershed Based on Geodetector: Burhatong River Basin, Northeast China as An Example

Changes in natural geographic features and landscape patterns directly influence the hydrology and non-point source pollution processes in the watershed; however, to slow down non-point source pollution, it is necessary to distinguish their effects. But the non-point source pollution process is interactional as a result of multiple factors, and the collinearity between multiple independent variables limits our ability of reason diagnosis. Thus, taking the Burhatong River Basin, Northeast China as an example, the methods of hydrological simulation, geographic detectors, and redundancy analysis have been combined to determine the impact of natural geographic features and landscape patterns on non-point source pollution in the watershed. The Soil & Water Assessment Tool (SWAT) has been adopted to simulate the spatial and temporal distribution characteristics of total nitrogen and total phosphorus in the watershed. The results show that the proportions of agricultural land and forest area and the location-weighted landscape contrast index (LWLI) are the main indicators influencing the rivers total nitrogen and total phosphorus. The interaction of these indicators with natural geographic features and landscape configuration indicators also significantly influences the changes in total nitrogen (TN) and total phosphorus (TP). Natural geographical features and landscape patterns have different comprehensive effects on non-point source pollution in the dry and wet seasons. TN and TP loads are affected mainly by the change in landscape pattern, especially in the wet season. Although the ecological restoration program has improved forest coverage, the purification effect of increased forest coverage on the water quality in the watershed may be offset by the negative impact of increased forest fragmentation. The high concentration and complexity of farmland patches increase the risk of non-point source pollution spread to a certain extent.