The relationship between sediment resuspension and light conditions has been studied in three shallow Dutch lakes. In shallow eutrophic lakes, the contributions of algae and suspended sediments to light attenuation are usually dominant. Wind induced resuspension of bottom sediment and sedimentation often determine the dynamics and the spatial variability of the suspended solids concentration and the light attenuation coefficient. A model is discussed relating the suspended solids concentration and light attenuation coefficient to the orbital velocity, induced by waves, and to the fall velocity of solids. Using experimental data, the relationships between fall velocity, organic matter content and the specific vertical attenuation coefficient are analyzed. Differences in the specific vertical attenuation coefficient and in fall velocities of sediment fractions, are related to differences in particle size as well as differences in composition. The contribution of (resuspended) particles to the suspended solids concentration and to light attenuation is primarily due to slow settling sediment fractions which are rich in organic matter. So in modelling light attenuation dynamics especially these fractions are of interest. Heavier fractions can be disregarded. A model for the relationship between resuspension and light attenuation dynamics, based on this conclusion, has been tested successfully for 2 shallow Dutch lakes.

No abstract

No abstract

In lake Marken (Markermeer), a shallow lake in the Netherlands, sediment transport and suspended solids concentration are dominated by wind induced resuspension of sediment. The suspended solids concentration in the lake determines the attenuation oflight. A 2-dimensional sediment transport model, STRESS-2d, was used to estimate the spacial distribution of the silt content for periods with different wind conditions. The model was calibrated using measured values of the fall velocity distributions of sediment, freshly deposited material and suspended solids. The specific light attenuation coefficient of the various sediment classes was also measured and used in the light attenuation model, CLEAR, together with simulation results from the STRESS-2d model, to simulate the light attenuation variations in time and space. By comparison of the simulation results for different scenarios, the influence of regional planning features on the sediment balance and the light attenuation can quantified. A provisional example of this method is presented.