Lake Ekoln
Lake Ekoln is situated at the mouth of the river Fyrisån about 10 km south of Uppsala, and is the largest basin in the northeastern part of Lake Mälaren. The core-to-core correlation in this lake is based on radiographs of more than 100 cores sampled during the period 1970 - 1990.
Partly overlapping radiographs of core 735 from a depth of 32 m in the outer part of the bay Granebergsviken in Lake Ekoln. Date of coring 1982-01-26. The chronology is based on correlations with radiographs of cores, sampled earlier in about the same area. The oldest of these X-rayed cores was sampled in 1970. For location, see the map below.
Bathymetric chart of Lake Ekoln with 2 m contour interval. Modified after Axelsson and Håkanson 1972 (UNGI Rapport Nr 14).
Lake Ekoln ( within the sections marked on the map above) has a mean depth of 19 m and a median depth of 22 m. The lake area amounts to 18.6 km2 and the water volume to 0.356 km3. The nominal residence time of the water is between 5 and 6 months.
Bottom-placed sediment traps has also been used for meauring sediment accumulation at selected station in Lake Ekoln. The measurements showed that the rate of sedimentation in the deeper basin parts was higher during the autumn, though the inflow of sediment from the feeding rivers was rather insignificant, than during the spring, when the main part of the annual sediment inflow took place. This was due to the autumn storms, that caused erosion, resuspension and transportation of sediment from shallower and steeper to deeper and flatter bottom parts.
Sediment discharge (pentad-media) at the mouth of the river Fyrisån and mean values of sediment accumulation in bottom-placed sediment traps during 5 measuring periods at a depth of about 20 m, 550 m in front of the mouth of the river Fyrisån in the bay Granebergsviken in Lake Ekoln (station no. 0202). Modified after Axelsson 1980 (UNGI Rapport Nr 52.
The calculated sediment inflow is mainly based on data of water discharge and suspended-sediment concentration, published by Kvarnäs (Kvarnäs, H., 1978: Dynamiska studier i Vänern och Ekoln. SNV, PM 1030). As shown by the diagram the rate of sedimentation was high during the autumn of 1971 though the inflow of sediment was insignificant. This was probably due to erosion, resuspension and transportation of sediment from the shallower parts of the river mouth area and the bay to the deeper parts.
The sediment-redistribution and the secondary transportation of sediment out from river-mouth areas is often underestimated but probably of great importance for the sediment accumulation within the deeper basin parts.
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