Spatial distribution and solubilization characteristics of metal(loid)s in riparian soils within reservoirs along the middle Jinsha River

The construction of large dams submerges riparian soils within reservoirs. However, little is known about the influence of water submergence on metal(loid) solubilization from polluted soils. In this study, the spatial distribution and solubilization characteristics of soil-associated metal(loid)s within reservoirs along the middle Jinsha River were evaluated. Concentrations of soil-associated metal(loid)s were determined and principal component analysis was performed to evaluate the metal(loid) spatial distribution. Then, metal(loid) chemical fractions of highly contaminated soils were analyzed. Finally, ex situ experiments of metal(loid) solubilization were conducted under the influence of changing pH, suspended solid concentration (SSC), and oxidation-reduction potential (ORP) conditions as well as successive drought-wetting cycles. Within the LY, AH, and LKK reservoirs, the soil-associated Ni and Cr originated from specific metal(loid) ores, and Cd and Cu remained from historical industrial pollution posed potential risks to water quality. Water submergence changed pH, SSC, and ORP conditions, which affected metal(loid) solubilization through dissolution-precipitation and sorption-desorption processes. The low SSC variables contributed to over 20% solubilization of total Cd, Cu, and As. Moreover, the neutral-alkaline conditions due to carbonate-dominated lithology limited metal(loid) release from soils. Finally, the decreased ORP promoted solubilization of metal(loid)s bound to Fe-Mn oxyhydroxides. Generally, the solubilization levels of metal(loid)s were dependent on the chemical fractions. Water submergence could induce potential solubilization of metal(loid)s, especially for Cd from historical industrial pollution. Thus, this study highlighted that the investigation on both spatial distribution and solubilization characteristics of metal(loid)s in riparian soils is important for future environmental management of reservoirs.