The influence of stratification on the amount and distribution of different settling particles in Lake Erken

Settling particles, especially settling organic particles, are important for the cycling of nutrients and contaminants because of their high adsorptive capacities. Therefore, the amount, distribution, and sources of settling particles were studied in Lake Erken, a moderately deep (mean depth 9 m, maximum depth 21 m) dimictic lake in central Sweden. The amount of settling particles was up to 45 times higher in hypolimnetic sedimentation traps than in epilimnetic traps during stratification (mean 7.0, median 5.2). However, immediately after the end of stratification, settling particles were almost evenly distributed in the water column. The same sedimentation pattern was observed for resuspended particles, whereas the flux of primary particles reaching the hypolimnion was not affected by stratification. These results indicate that during stratification, resuspended particles in Lake Erken originate in the hypolimnion where they remain. Because surface waves cannot cause sediment resuspension in the moderately deep hypolimnion of Lake Erken, internal seiches are suggested to be responsible for the high amount of settling particulate matter in the hypolimnion during stratification.