Artificial water regulation and natural flood processes control heavy metal concentrations and transport in the Yellow River, China.

Based on heavy metals daily observation at the Lijin station during water-sediment regulation (WSR) event and three natural floods in 2020, we examined the effects of different flood events on heavy metal in lower Yellow River, China. The results revealed that due to different water and sediment sources and processes influencing heavy metals dynamics, the dissolved Cr, Zn As and particulate heavy metals during natural flood events were higher than those during WSR event. Dissolved heavy metals increased during water regulation and decreased during sediment regulation. Using positive matrix factorization (PMF) model, we found that sources of dissolved heavy metals during WSR event were mainly from agricultural practices, rock and soil weathering, and industrial pollution. During flood events, particulate heavy metals' concentrations varied due to dilution, human activities, and reservoir influences, with industrial and agricultural sources significantly impacting Cu, Zn, As, and Pb levels.