Sediment resuspension in a shallow lake with muddy substrates: St Lucia, South Africa

Abstract

Wind-driven sediment resuspension affects the physical and biological environment of the water column in shallow estuarine lakes. This study investigated the relationship between wind-driven waves and suspended sediment concentration (SSC) using the 33km2 South Lake basin of Lake St Lucia, South Africa as a case study. Five wave poles measuring significant wave height and turbidity were deployed over an aggregate period of twenty days at distributed locations where sediment substrate compositions varied from muddy to sandy and depths ranged from 0.7m to 2.1m. The resulting turbidity dynamics were used to test a simple depth-averaged model of suspended sediment concentrations. The model performed best in the muddy regions of the lake and was able to simulate the resuspension dynamics more accurately than the settling dynamics. Peak suspended sediment concentration levels were best captured for the deeper muddy locations. The model provides a means to make spatially explicit predictions of suspended sediment concentrations that can be used to understand the forcing mechanisms for primary producer growth and distribution or to improve sediment budget calculations.