Trace metal behavior in sediments of Jiulong River Estuary and implication for benthic exchange fluxes

Severe metal pollution due to industrial effluents releases has been documented in Jiulong River estuary, Southern China. However, integrated understanding of trace metal behavior in the sediment is lacking. In the present study, DGT (diffusive gradients in thin films) technique was employed together with sediment cores to study the porewater dynamics of trace metals as well as the benthic exchange fluxes from four sampling sites over three different months. The sedimentary environment showed distinct spatial and temporal variations due to effluent discharge and biological activities. Metal behavior was controlled by early diagenetic reactions below the interface, in suboxic layer and in deeper sediment. Precipitation as sulfides and adsorption onto Mn/Fe (hydr)oxides were important in scavenging trace metals. Estimated exchange fluxes at sediment-water interface in this estuary indicated that the overlying water was a major source for trace metals, whereas sediments could also be the source if surface remobilization (Mn/Fe reduction) dominated. Our results highlighted the impacts of both natural and anthropogenic processes on the source, fate and transformation of trace metals in this dynamic system.