Helsinki 2008

Sediment resuspension, the return of the bottom material into the water column, is an impor-tant process that can have various effects on a lake ecosystem. Resuspension – caused by wind-induced wave disturbance, currents, turbulent fluctuations and bioturbation – affects water quality characteristics such as turbidity, light conditions, and concentrations of sus-pended solids (SS) and nutrients. Resuspension-mediated increase in turbidity may favour the dominance of phytoplankton over macrophytes. The predator-prey interactions contributing to the trophic state of a lake may also be influenced by increasing turbidity. Directly, the trophic state of a lake can be influenced by the effect of sediment resuspension on nutrient cycling. Resuspension enhances especially the cycling of phosphorus by bringing the sedimentary nu-trients back into the water column and may thereby induce switches between phosphorus and nitrogen limitation. The contribution of sediment resuspension to gross sedimentation, turbidity, and concen-tration of SS and nutrients was studied in a small, deep lake as well as in a multibasin lake with deep and shallow areas. The effect of ice cover on sediment resuspension and thereby on phosphorus concentrations was also studied. The rates of gross sedimentation and resuspen