Sedimentary Footprint of the Eurasian Beaver (Castor fiber L.) in Small Rivers of European Russia in the Landscape–Climatic Context

In recent decades, the number of beavers both in Russia as a whole and its European part has increased significantly due to reintroduction, conservation measures, etc., which has partially resulted in changes in the water regime, especially of small rivers, erosion and sedimentation processes in them, and a partial transformation of riparian ecosystems. Based on the results of 2022–2024 field work and laboratory studies, spatiotemporal features of changes in the rate of sedimentation, grain-size distribution, and organic matter content in bottom sediments of beaver ponds in 15 small rivers of the southern forest, forest–steppe and steppe landscape–climatic zones of the Volga–Kama region of the East European Plain were revealed. It was found that the highest rates of sediment accumulation, the largest proportion of fine grain-size fractions (<0.01 mm), and the highest content of total organic matter in the bottom sediments of beaver ponds are observed in small rivers of the steppe zone, while the smallest indicators of the above are characteristic of small rivers in the southern forest zone. Moreover, the highest rates of sedimentation are observed in the ponds of the upper reaches of small rivers in the studied zones. The distribution of sedimentation rates in beaver ponds demonstrates distinct seasonal dynamics: the highest rates of sediment accumulation are observed during the spring flood caused by snowmelt, while lower rates occur during the summer–autumn low-water season with episodic rainfall flood events, especially during a prolonged absence of the latter. Using two rivers in the forest–steppe zone as an example, the rates of total sedimentation in beaver ponds were identified (1.3–14.7 cm per year), which correlate well with the rates of sedimentation in beaver ponds of small rivers in various lowland/upland regions of Europe.