Response of redox zoning and microbial community structure in riverbed sediments to the riverbed scouring during bank filtration

Abstract

Riverbed sediments are an important zone and interface for the interaction of surface water and groundwater; hence, biochemical processes in the riverbed sediments are critical to maintain the ecology of the system and water quality. Riverbed sediment scouring can substantially alter the hydrodynamic conditions of river water infiltration and redox conditions at the surface–groundwater interface, which in turn affects the biochemical processes. Currently, in-depth understanding of the distribution characteristics of the microbial community structure in riverbed sediments, especially their response to riverbed scouring, is lacking. This study revealed the temporal and spatial changes in redox indicators in the Liaohe riverbed sediment and discussed the response of the microbial community to the influence of riverbed scouring. The results showed that during the investigation period (September to November 2020), the riverbed sediments in the river reach were generally in a state of scouring in the low water stage, and the scour depth was 4–9 cm. The redox zone in the nearshore area moved up by 5.5–23 cm, and moved down by 0.1–10 cm in the intermediate transition area and the center of riverbed, and the maximum overlapping depth of the redox zone could reach 50 cm. The relative abundance of dominant bacteria species had a good correlation with the intensity of geochemical reactions, decreasing in low-water levels close to the center of the riverbed, which further indicated the weakening of the reduction rate. Influenced by riverbed scouring, the species of denitrifying bacteria in the surface layer increased, multiple dominant bacteria of iron, manganese and sulfate often coexist in deep riverbed sediments, and were slightly different in the low water level. The results provide a better understanding of the chemical composition of the pore water in the riverbed sediments, which are of great significance for maintaining the ecological safety of river water.