Influence of sediment resuspension on the light conditions and algal growth in Lake Balaton

Abstract

Wind-induced sediment resuspension and its impact on the light conditions were intensively studied in three basins of Lake Balaton, a large shallow lake in Hungary, which is subject to eutrophication. The depth ranges between 2 and 5 m. Frequent observations were made of the wind, the water flows and waves, the suspended solids (ss) concentration, the Secchi disc depth and the light conditions. Four versions of the model were developed for describing the temporal changes in the ss concentration. Models of similar structures were applied for the extinction coefficient and the Secchi disc depth. Several methods were used for calibration. Identifiability and arbitrariness of the model structures have been studied. The extinction model was coupled to a known mass balance equation describing temporal changes in the algal biomass. Sensitivity analysis using hypothetical step-like wind inputs has shown a considerable change in the light limitation factor as compared to the case of steady state winds. Finally, the coupled extinction-algae biomass model was used in a Monte Carlo fashion when longer subsets were selected at random from past wind observations. Late summer conditions and parameters typical for the most eutrophic basin of Lake Balaton (where nutrients are no longer limiting) were selected. The analysis has demonstrated that, in harmony with the observations, the wind has a major impact on the short-term changes of algal biomass. The approach outlined can be utilized to improve the earlier ecosystem models applied for Lake Balaton. The methodology developed is transferable to other shallow lakes.