Spatial distribution of heavy metal contaminants: The effects of water-sediment regulation in the Henan section of the Yellow River

Water-sediment regulation (WSR) affects sediment transport in the middle and lower reaches of the Yellow River through periodic interception of sediment by dams and alteration of downstream flow rates, which leads to redistribution and recycling of elements. In this study, based on the evaluation of seven heavy metals (V, Cr, Ni, Co, Cu, Zn, and Cd) in water, sediment and suspended particulate matter (SPM) in the Henan section of the Yellow River, the effects of WSR on the redistribution and risk of release of metals to the downstream aquatic environment were investigated, and the range of impact and pollution sources were determined. Dissolved metals were well below guideline values for water quality, but Cd, Cr, and Cu were enriched in the sediments, especially in the reservoir, and the pollution load index (PLI) results indicated that the contamination in the study area remained very low. The level of contamination was decreased, and metals migrated downstream after WSR. The chemical speciation of metals indicates that anthropogenic input of metals occurs in upstream tributaries, and the risk of release of metals in the sediments increases after WSR, but the spatial distribution of the risk is more homogeneous. The distribution coefficient explains the distribution pattern of pollution, where SPM carries pollutants to the downstream while formed surface sediments through natural deposition during the sand-discharge stage. Based on geological and field investigations, upstream gold mining and downstream riverbank cultivation activities in the study area are potential sources of Cu and Cd pollution. These findings are crucial to the better understanding of patterns of metal release from artificial impoundments in river systems and provide a theoretical basis for ecological development in the Yellow River Basin.