The settling of resuspended lake sediment related to physicochemical properties of particles of different sizes: Implication for environmental remediation

Abstract

Sediment resuspension is an important way for shallow lake internal pollution to interact with the overlying water column, and the pollution risks are reasonably related to the retention of resuspended sediment particles in overlying water. In the current study, the settling of resuspended sediment particles was comprehensively investigated under different disturbances using five urban lake sediments. The results show that the particle size distributions of resuspended sediment from different lakes exhibited similar variations during settling with disturbance, although varied settling times were observed under static conditions. During settling with and without disturbance, sediment particle sizes were mainly within 8–63 μm at the initial stage, and were < 8 μm in the later stages of settling. Based on these settling characteristics, the sediment particle size was divided into sand (> 63 μm), silt (8–63 μm), and very fine silt and clay (< 8 μm) fractions. Kinetic analysis suggested that sediment settling for different particle sizes could be well described by the first- and second-order kinetic equations, especially when settling was disturbed (r2 = 0.727–0.999). The retention of resuspended sediment could be enhanced as particle sizes decreased and disturbance intensities increased. Furthermore, a water elutriation method was successfully optimized, with separation efficiencies of 56.1%–83%, to separate sediment particles into the defined three particle size fractions. The chemical compositions of sediment were found to change with different particle sizes. Typically, calcium tended to form large-size sediment, while the total contents of aluminum, iron, magnesium, and manganese showed significantly negative correlations with sediment particle sizes (p < 0.01) and tended to distribute in small-size particles (e.g., < 8 μm). Overall, the sediment particle size related settling dynamics and physicochemical properties suggested the necessity on determining the pollution of resuspended sediment at different particle sizes for restoration of shallow lakes.