SEDIMENT RESUSPENSION AND LIGHT CONDITIONS IN SOME SHALLOW DUTCH LAKES

The relationship between sediment resuspension and light conditions ha s been studied in three shallow Dutch lakes. In shallow eutrophic lake s, the contributions of algae and suspended sediments to light attenua tion are usually dominant. Wind induced resuspension of bottom sedimen t and sedimentation often determine the dynamics and the spatial varia bility of the suspended solids concentration and the light attenuation coefficient. A model is discussed relating the suspended solids conce ntration and light attenuation coefficient to the orbital velocity, in duced 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, Diffe rences in the specific vertical attenuation coefficient and in fall ve locities of sediment fractions, are related to differences in particle size as well as differences in composition. The contribution of (resu spended) 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 dynamic s especially these fractions are of interest. Heavier fractions can be disregarded. A model for the relationship between resuspension and li ght attenuation dynamics, based on this conclusion, has been tested su ccessfully for 2 shallow Dutch lakes.