Assessing the Impacts of Land Use Patterns on Nitrogen and Phosphorus Exports in an Agricultural Watershed of the Lijiang River Basin

The nitrogen and phosphorus pollution in water is highly related to the land use pattern in watershed. The impacts of the land use patterns on total nitrogen (TN) and total phosphorus (TP) exports in an agricultural watershed of the Lijiang River Basin were studied using the Soil and Water Assessment Tool (SWAT). The SWAT performed well in simulating the runoff, TN and TP export. The correlation analysis showed that the forest land negatively affected the simulated TN and TP exports, while the orchard, cultivated land, and building land had positive effects. The results of classification and regression tree models showed that ED was the primary landscape factor affecting the TN and TP exports and followed by PLAND and LPI. Then the scenario simulation was conducted to analyze the effects of land use conversion on the TN and TP exports using the calibrated and validated SWAT. The results showed that the TN and TP exports significantly increased under the conversion of the other land use types into the building land, cultivated land, and orchards and the increasing rate decreased in order, while the rising forest and water body area reduced the TN and TP exports. Generally, the changing rates of TN exports under landuse conversion were higher than those of TP exports, except for the orchard conversion. This study revealed that the reasonable planning of land use could alleviate nitrogen and phosphorus pollution, which was helpful for aquatic ecosystem restoration.