ABSTRACT
It is generally accepted that both climatic fluctuations and changes of land use patterns can exert substantial influence on spatial and temporal characteristics of sediment redistribution in a fluvial system. However, in most cases it is extremely difficult to distinguish natural signals from anthropogenic impacts as well as to obtain reliable quantitative characteristics. In this study an attempt has been made to evaluate such contributions by reconstructing temporal and spatial variability of fluvial sediment budgets for small river basins with small reservoirs at their outlets and different land use histories. As important and efficient sediment interceptors, small reservoirs in agricultural areas are used as sources of valuable information on catchment scale erosion and sediment delivery (Verstraeten & Poesen 2001). In addition, reservoirs are also important as sinks of sediment-associated pollutants (Golosov et al. 2012) and organic carbon (Cole et al. 2007).
Small reservoirs located in dry valleys or on small streams and rivers are typical and important components of human-altered landscapes of the European Russia agricultural belt. Initially their widespread introduction in 19th Century was mainly aimed at interception of peak runoff for local water supply and (on perennial streams) providing continuous hydropower supply for water mills. At present such small reservoirs are utilized in diverse ways from local water supply for crops and livestock to local fishery and recreation.
Two small river basins located in the Seim River basin (Kursk Region, Western European Russia) have been investigated in this study. Selection of the case study sites considered in this study was based on representativeness of local topography, catchment morphometry (area, valley network structure), soil cover, land use and crop rotations. Several independent techniques including radioisotope tracers, soil surveys, geomorphic mapping, remote sensing data analysis and soil erosion modeling have been employed for evaluating sediment budgets for the studied basins. Detailed microstratigraphic separation of the reservoir infill sediment was based on sediment core descriptions and 137Cs depth distribution analysis Results of the investigations clearly show that the importance of catchment-scale land use changes for the reservoir sediment delivery and sedimentation depends largely upon the catchment area, sediment transfer distance, presence and efficiency of intermittent sediment sinks. Temporal dynamics of the latter also needs to be evaluated. The most general tendency observed is decreasing sediment delivery into reservoirs and increasing redisposition within small dry tributary valleys. Sediment budget and reservoir sedimentation variability of the two studied basins over the last decades have been largely controlled by natural tendency of decreasing spring snowmelt runoff and increasing frequency of heavy summer rainstorms accompanied with land use changes associated with collapse of the socialist-type economy, general economic disorder of 1990s – early 2000s and gradual recovery of industry and agriculture approximately since 2005.
