梯级水库联合运行下河流水质时空变化特征研究OA

In this study,we explored the spatiotemporal variation of river water quality and potential driv-ing factors under the joint operation of four cascaded reservoirs(Wudongde,Baihetan,Xiluodu,and Xiangjiaba reservoirs)in the lower reaches of Jinsha River.We aimed to fill the research gap in the long-term evolution of water quality under the four-reservoir joint operation scenario and provide scientific sup-port for watershed water quality management and the ecological operation of reservoirs.The study was based on monthly water quality data from 22 monitoring sections in the lower Jinsha River from 2016 to 2023.Multivariate statistical methods including the Mann-Kendall trend test,principal component analy-sis(PCA),Kruskal-Wallis H test and Dunn's test were adopted to systematically evaluate the variation of key water quality indicators,including pH,DO,CODMn,TP,NH3-N and TN.Key results are as follows:(1)The overall water quality in the lower Jinsha River is improving.The proportion of sites meeting Grade Ⅰ water quality standards increased from 44.67%during the two-reservoir operation period(2016-2019)to 78.07%during the four-reservoir joint operation period(2022-2023),and no sites with water quality worse than Grade Ⅲ.The mean value of the water quality index(WQI)rose from 96.31 to 98.77.(2)Temporally,the concentrations of CODMn and TP generally decreased,while TN concentration increased significantly.(3)Spatially,TN concentration and pH gradually increased from upstream to downstream,but the NH3-N concentration decreased.CODMn and TP concentrations tended to stabilize in the downstream Xiangjiaba reservoir and protected river reach.(4)Significant differences in water quality were observed among different regulatory periods.TN and TP concentrations during impoundment and flood season were generally higher than those during drawdown.While altering hydrological regimes,cas-caded reservoirs have also reshaped the spatiotemporal pattern of water quality,with particularly remark-able changes in nitrogen and phosphorus.We recommend strengthening control of agricultural non-point source(NPS)nitrogen pollution in the watershed and intensifying management of nitrogen and phospho-rus inputs during impoundment and flood season to reduce the risk of eutrophication.