Evaluating the impacts of inter-basin water transfer projects on ecosystem services in the Fenhe River Basin using the SWAT model

Inter-basin water transfer (IBWT) projects have been widely constructed to alleviate the pressure on water resources in water shortage basins. However, the ecological effects of IBWT projects have often been ignored. Based on the Soil and Water Assessment Tool (SWAT) model and a constructed total ecosystem services (TES) index, the impacts of IBWT projects on recipient basin ecosystem services were analyzed in this study. The results showed that the TES index was relatively stable from 2010 to 2020, but in the wet season it was 1.36 times that of the other months with high water yield and nutrient loads. Spatially, areas with high index values were mainly distributed in the sub-basins around the reservoirs. The IBWT projects had positive impacts on ecosystem services, and the TES index with IBWT projects was 5.98% higher than that without projects. Water yield and total nitrogen were the two most affected indexes, with increased of 5.65% and 5.41%, respectively, under the impacts of IBWT projects. Seasonally, the change rates of the TES index were less than 3% while the change rates of water yield and nitrogen load peaked at 8.23% and 53.42%, respectively, in March, owing to the large amount of water released from the reservoirs. Areas affected by the three evaluated IBWT projects accounted for 61%, 18%, and 11% of the watershed, respectively. Under the impact of each project, the TES index generally increased, whereas the impact decreased as the distance from the inflow location increased. Intense changes in ecosystem services occurred in sub-basin 23, the sub-basin closest to an IBWT project, with water yield, water flow, and local climate regulation increasing the largest.