Effects of water and sediment discharge regulation on sediment environment in the Yellow River Estuary and adjacent waters

Based on geochemical properties of sediment observed in Yellow River Estuary during the water and sediment discharge regulation (WSDR) project period, 2020, the changes of the content and distribution characteristics of major sediment factors in the surface sediment were analyzed, and ecological risk assessment and pollution source analysis were conducted on heavy metals. The results showed that the contents of silt and sand were higher than that of clay, and the content of silt increases, while the content of sand and clay decreases during WSDR project; The sulfide content did not change significantly during WSDR process, while the organic carbon content increased significantly in the middle and later stages; The WSDR project leads to an increase of the contents of Cd, Cu, and Zn, while the contents of other heavy metals did not change; Cadmium was determined as the principal ecological risk factor, and its contribution ratio was the highest among six studied elements. Cd pollution in the middle and later stages was more severe than early stages which was affected by WSDR project. Pearson correlation coefficient between environmental factors showed that sediment grain size and organic carbon were two important factors in the distribution of heavy metal of cadmium、copper and zinc; other heavy metals had no obvious correlation with grain size, which may be caused by comprehensive factors. The analysis of pollution sources indicated that Cd, Pb, Cu, As, and Zn mainly come from composite pollution sources such as natural weathering, terrestrial river input, and fossil fuel extraction such as oil and gas; Hg mainly come from atmospheric sedimentation pollution and was not significantly affected by WSDR project.