Behaviour and quantitative source analysis of heavy metals in pore water profiles at the Inlet of Dongting lake from the Xiangjiang river

The risk of heavy metal (HM) release from sediments is increased by strong hydraulic gradients and intricate water-sediment exchange processes at river-lake junctions. In this paper, taking the inlet of Dongting Lake from the Xiangjiang River as an example, the spatial distribution, diffusive flux, toxicity, and quantitative sources of heavy metals (Fe, Mn, Cr, Ni, Cu, Zn, As, Cd, and Pb) in pore water profiles were investigated. The study results show that the concentration of HMs in the pore water is higher than that in the overlying water. Except for Ni, the average concentrations of the remaining HMs in the pore water exceeded the standards. The concentrations of HMs generally increased with depth, and HMs in the river group fluctuated more in the vertical direction than in the river-lake mixed group. The APCS-MLR model resolved that the sources of HMs in pore water can be categorized into three main groups, namely, "mixed sources" under the joint control of industry and agriculture, natural sources, and mining sources, which contributed 46.83%, 34.15%, and 19.02%, respectively. Diffusive fluxes indicate that sediments are a direct source of HMs in overlying waters. According to the Nemerow Index (NI), the effects of Cd and Pb are primarily responsible for the significant impact of pore water quality conditions in the study area. Therefore, environmental protection strategies in the study area should focus on Cd and Pb pollution.