Interactions between abiotic and biotic variables strongly affects the light transmission in eutrophic, shallow lakes, and thus affects submerged vegetation. Seasonal changes in interactions can completely change the conditions and enable re-establishment for submerged vegetation. Aim of this thesis was to examine how interactions between phytoplankton, zooplankton and resuspended sediment influence light transmission during a critical phase for establishment of submerged vegetation. This was done by study the development of interactions in Lake Tåkern, southern Sweden, by sampling water variables during spring and summer of 2016. Additionally, a laboratory experiment was done to examine how zooplankton (Daphnia sp) is affected by high levels of turbidity.

Results of this study is: Phytoplankton biomass contributed to inhibit light transmission and contributed to resuspended sediment in April-June. For July-August, resuspended sediment consisted mostly of detritus material and inorganic solids, but phytoplankton still contributed in large extend to inhibit light transmission. Zooplankton density and biomass affected phytoplankton biomass by grazing. Zooplankton density in general did not seem to be affected by temporary high turbidity, but some Cladocerans were more sensitive to disturbances.

Light transmission in shallow, eutrophic lakes is affected by several variables. Other than the variables studied in this study, this years’ water levels were unusually low in L. Tåkern. This have contributed to re-establishment of submerged vegetation.