Influences of riverbed siltation on redox zonation during bank filtration: a case study of Liao River, Northeast China

The upper part of riverbed sediment is one of the key interfaces between surface water and groundwater, and biogeochemical process in this interface has a profound influence on the chemistry of infiltrated water. The lithology and permeability of bed sediment is mainly controlled by variation in river hydrodynamic conditions. However, there have been few studies of the effect of riverbed siltation on the hydrochemistry and redox reactions of infiltrated water due to the high variability in these processes and challenges associated with sampling. This study selected and examined a river channel near a site of riverbank filtration by drilling on the floating platform and conducting microelectrode testing and high-resolution sampling. The hydrodynamic and chemical characteristics of pore water in and lithologic characteristics of riverbed sediment, the siltation, and redox zone were examined and compared. Differences in hydrodynamic conditions changed the lithology of riverbed sediment, consequently affecting redox reactions during the process of river water infiltration. Variations in siltation changed the residence time of pore water and organic matter content, which ultimately resulted in differences in extension range and intensity of redox reactions. This study provides a valuable reference for understanding the effect of riverbed siltation on water quality of riverbank infiltration.