Resuspension in regulating sedimentation dynamics in Lake Vesijärvi.

Abstract

The role of resuspension in sedimentation dynamics and internal phosphorus (P) loading was investigated in the Enonselka basin of Lake Vesijarvi, southern Finland. The gross sedimentation rate was measured at three sampling sites, where sedimentation traps were placed 2 m above the bottom (the depth of 28 m, 18 m and 7m) and at the two deepest sites also in the metalimnion (11 m depth). The total settling flux did not follow either the phytoplankton biomass development in the lake or the bacterial mineralization rate in the settled material. The gross sedimentation rate was much higher in the hypolimnion than in the metalimnion, indicating that resuspension increased the settling flux. This conclusion is supported by the fact that when the gross sedimentation rate increased, the C and N concentrations of settled material resembled those of bottom sediment. The proportion of resuspended material, estimated by three different methods, averaged 56-99 % of the gross sedimentation rate during the study periods. Contrary to the common assumption, the Enonselka basin provides an example of successful restoration by biomanipulation in lakes with high resuspension.