The Impact of Hydraulic Hubs on the Spatial Variation of Water Quality in the Middle Reaches of the Hanjiang River and an Analysis of the Driving Factors

The Hanjiang River occupies a very important position in China's water resource allocation and is a typical dam-influenced river in China. To monitor the water quality and heavy metal content of the river, and to investigate the influence of water hubs on the changes of both, sampling sites were set up in October 2020 upstream, before, and below the dams of three typical water hubs in the middle reaches of the Hanjiang River for analysis and investigation. The results showed that the concentrations of TP, TN, NH4-N, and Fe exceeded the standard; the concentrations of conventional water quality indicators changed significantly (P < 0.01) along and before and after the dams, and generally showed an increasing trend before and after the Wangfuzhou and Cuijiaying water conservancy hubs; the concentrations of Cr differed after the dams (P < 0.05); the distribution of TP in the vertical direction was significantly different (P < 0.05), the bottom layer concentration before the dam is 2–3 times higher than the surface and middle layer concentration; Fe concentration in the water conservancy hub before the accumulation of the bottom layer, the rest of the heavy metal concentrations in the horizontal and vertical distribution are not significantly different (P > 0.05).