An empirical model for sediment resuspension in shallow lakes

Suspended solids concentrations were measured at routine 2-3 week intervals and on additional windy days for at least one year in each of seven shallow (mean depth < 2 m) South Island, New Zealand lakes. Surface wave characteristics were estimated from water depths and local meteorological data using a shallow-water wave forecasting model for fetch-limited waves. Bottom shear stresses were computed from surface wave characteristics for the sampling stations and for a hypothetical lake-average station. The calculated shear stresses were, on average, much better predictors of suspended solids concentrations than alternative models using two different functions of wind speed, wave height(2)/depth or wavelength/depth. A combination of the sample station and lake average shear stresses provided slightly better predictions than the sample station values alone, suggesting that currents also contribute significantly to the concentration at a given point. Regressions of suspended solids on the combined function had r(2) values ranging from 0.47-0.73 in the seven lakes. The slopes of these regressions were negatively related to the settling velocity of the lowest quartile of the sediment, and to macrophyte biomass, in multiple regression (r(2) = 0.94, p < 0.01).