Original paper

Sedimentation and resuspension dynamics in Lake Vesijärvi (Finland): comparison of temporal and spatial variations of sediment fluxes in deep and shallow areas

Tammeorg, Olga; Niemistö, Juha; Horppila, Jukka; Haldna, Marina; Kangur, Külli

Abstract

The aim of this study was to elucidate temporal and spatial variations in sediment fluxes in the Enonselkä basin of Lake Vesijärvi, where traps covering deep and shallow areas of the lake were deployed. Moreover, the study was designed to compare sediment fluxes from deep and shallow areas. The findings show that both the gross sedimentation rate and the resuspension rate were significantly higher in the stratifying region (> 20 m depth) than in the shallower parts of the lake. Resuspension was of major significance in controlling sedimentation dynamics in the Enonselkä basin, an area where recent challenges to lake management have been encountered. The results of the study indicate that the rate of sediment resuspension followed the same pattern as gross sedimentation during the open water period, and this differed significantly between sampling dates; that is, notably higher values for resuspension were observed in June and September, when the average rates were measured as 21.5 and 32.1 g dw m−2 d−1, respectively. The bottom processes were found to be related to wind and convective mixing. Moreover, high rates of resuspension were associated with the large pool of organic material accumulated during strong phytoplankton blooms. The load of suspended solids derived from the shallower areas (218 t d−1) was twice that from the deeper areas (110 t d−1). The exchange processes across the sediment-water interface in the shallow areas are of overriding importance in controlling sediment fluxes and the water quality in Lake Vesijärvi.

Keywords

sediment resuspensiongross sedimentationtemporal and spatial variationsdeep and shallow areasstratifying lakewater turbidity