Accumulation and migration of particulate trace metals by artificial flood event of the Yellow River: From Xiaolangdi reservoir to estuary

Reservoir construction increasingly alters the natural transport of riverine water and sediment to the sea, including the trace metals and other pollutants. In 2018, an intensive flood event and 412 million tons of sediment were released from the Xiaolangdi dam during the water-sediment regulation of Yellow River, one of the world's largest sediment releases. During the artificial flood event, the surface sediments in Xiaolangdi Reservoir (XLD) and the Yellow River estuary, suspended sediments at Lijin Station were collected. The concentration and speciation of particulate Cr, Ni, Cu, Zn, Cd and Pb, as well as the major geochemical composition were analyzed, to characterize the behaviors of the metals from the reservoir to estuary mixing zone, and elucidate the controlling mechanisms. The results showed that for exogenous phases, Cr, Ni, Cu and Zn were likely bound to the Fe-Mn oxides, whereas Pb and Cd were mainly adsorbed in the carbonates. The trace metals in XLD were stably combined with fine-grained bottom sediments at high concentrations before dam release. During the delivery from reservoir to downstream channel, the binding of Cr, Ni and Cu with Fe-Mn oxides was markedly enhanced. Pb and Cu showed obvious migration from carbonates to Fe-Mn oxides, and Cd and Pb were even released into the water. The accumulation and migration of trace metals were controlled by the adsorption of fine-grained components, especially Fe-Mn oxides and carbonates, and influenced by the oxidizing processes. After entering the estuary, the trace metals were greatly scavenged by reservoir-sourced fine particles, tended to bound to organic matter affected by the reducing environment. Our results suggest that dam

Automated summary

Reservoir construction has a significant impact on the natural transport of riverine water and sediment, as well as trace metals and pollutants. This study found that the migration and accumulation of trace metals were influenced by the adsorption of fine-grained sediments and oxidative processes. In the estuary, the trace metals were scavenged by reservoir-sourced fine particles and affected by the reducing environment.