[Water Quality Evaluation and Spatial-temporal Distribution Characteristics of the East Route of the South-to-North Water Diversion Project in Jiangsu Province Based on WQI].

The east route of the South-to-North Water Diversion Project in Jiangsu Province was used as an example to investigate the characteristics of changes in water quality in the area affected by significant water diversion projects. Based on the comprehensive assessment method of the water quality index （WQI）, the M-K trend test, and the geographic information system （GIS）, the spatial and temporal variation characteristics of water quality in the 13 national assessment sections of the east route of the South-to-North Water Diversion Project in Jiangsu Province were evaluated and analyzed from 2013 to 2022. The results showed that the water quality assessment grades in the study area were mainly "medium" and "good." The overall mean value was 74.03, indicating "good" water quality. DO, BOD₅, and NH₄⁺-N were the primary indicators of changes in river water quality in the region. Over time, the water quality in the basin had significantly improved from 2013 to 2022. However, there was a rebound in 2021, but this phenomenon was effectively controlled in 2022. Water quality was better during the non-flood season compared to that during the flood season. From a spatial perspective, the water quality in the southern part of the region was superior to that in the north. Furthermore, the rate of improvement was faster in the south. This could be attributed to factors such as precipitation, population density, and the scale of agricultural and livestock activities. However, the water quality of the S11 （Sanduoxi Bridge） section was generally lower than that of other sections and should be given further attention.