Influence of salinity and sediment resuspension on macrophyte germination in coastal lakes

The vegetation as well as diaspore banks were investigated in two coastal lakes on the German Baltic Coast. The distribution of vegetation and diaspores was analysed at two depths (0.5, 1.5 m) on transects. Seedling densities and germination rates of the diaspore banks were determined in a laboratory study that investigated dependencies on salinity and sediment resuspension. The vegetation study yielded five taxa in both lakes: 3 angiosperm taxa and 2 charophytes. In contrast to the poorly developed vegetation, the diaspore bank was represented by 12 taxa(-groups). The germination experiments showed five taxa. Chara contraria A. Br. ex Kütz. was the dominant species. The seedling density of this species was significantly lower at the highest salinity after sediment resuspension in one of the two lakes. The second lake showed a significantly lower seedling density at the highest salinity only for one water depth before sediment resuspension. After sediment resuspension within a salinity level, the seedling density and germination rate were as high as prior to this disturbance. Sediment resuspension can buffer the recolonisation from the sediment diaspore bank of Chara contraria after drawdown.