Dynamic behavior of sediment resuspension and nutrients release in the shallow and wind-exposed Meiliang Bay of Lake Taihu

Abstract

Wind-induced sediment resuspension frequently occurs in Lake Taihu, a typical large shallow lake in China. Internal nutrients release accompanied by sediment resuspension is supposed to sustain the eutrophic status and algal boom persistence. In this study, high-frequency and synchronous in situ observation of the wind field, currents, waves, suspended sediments, and nutrients were collected to understand the dynamic behaviors of sediment and nutrients under multiple natural disturbances in Meiliang Bay, Lake Taihu. Results suggest that both wind speed and wind fetch length could effectively activate the sediment layer and trigger particles entrainment into the overlying water. Wind speed of 4 m/s with long wind fetch (between east and southeast wind direction) was the critical value for sediment resuspension. Furthermore, wind-induced wave shear stress and stochastic nature of turbulence at the water-sediment interface were the driving force for sediment resuspension. Specifically, incipient motion of sediment occurred when shear stress was ranging from 0.02 to 0.07 N/m2. Wind-induced sediment resuspension had significantly contributed to nutrients release of particulate N and P, whereas dissolved nutrients concentration was less affected. Internal nutrients release by wind could maintain a significant potential for obstinate eutrophication and algal bloom. This study has revealed the dynamic response of nutrients release to sediment resuspension and wind-induced hydrodynamics. Therefore, a better understanding of the mechanism of internal nutrients release will benefit the effective and sustainable management of the shallow and wind-exposed lakes.