Lutra 46(2)_Gorshkov_2003

Is it possible to use beaver building activity to reduce lake sedimentation?

Erosion processes and lake sedimentation are among the major environmental problems in Tatarstan Republic. Ploughed soils from the agricultural lands are easily washed away from the fields during flooding, and carried through rivers and relief depressions to lakes and bogs, which then fill with the sediment. Raifa Lake is an example of such lake degradation. Due to erosion from agricultural lands upstream from the lake its length has decreased from 6 to 1.3 km since 1650, its maximum depth has decreased from 36 to 19 m, and its area has decreased from 150 to 32 ha. The possibility of “harnessing” beavers (Castor fiber) to stop sedimentation by building dams is of great interest. We hoped that dams constructed by beavers would reduce the volume of solid particles that flow into Raifa Lake. With this objective in mind, we reintroduced 21 beavers between 1996 and 2000 on the Sumka River, which runs through Raifa Lake. Investigation was done during the annual flooding periods of 1999-2001 when 115 water samples were taken. The main factor that affects sedimentation is the volume of water that can be stopped by beaver ponds. During the flooding period of 2001, 4,250 tons of solid particles were stopped by three beaver dams in the settlement on Sumka River amounting to a cumulative area of 5.2 ha. Sediment mass per litre of water decreased by 53% (from 0.49 to 0.26 g/l) after water had passed the cascade of three dams.