The impact of contemporary changes in climate and land use/cover on tendencies in water flow, suspended sediment yield and erosion intensity in the northeastern part of the Don River basin, SW European Russia

Abstract

The basin of the Don River (the fifth longest river in Europe), located mainly in the forest-steppe and steppe landscape zones, is one of the most populated and agriculturally developed regions of the East European (Russian) Plain. Sheet, rill and gully erosion occurring chiefly in snowmelt period (March-April) and also in moderate-to-heavy-rainfalls season (chiefly May-to-September) is the main factor of present-day soil degradation within cultivated lands of this basin. Using monitoring hydrological data, it is shown, by the examples of the Khopyor River and the Medveditsa River flowing in the northeastern part of the Don River basin (SW European Russia), that suspended sediment yield of the rivers, as an objective and sufficiently accurate indicator of total erosion intensity in river basins, was reduced by 3.6-3.8 times between the 1960s-1970s and 2008-2015. This conclusion is consistent with change in sedimentation rates (using ¹³⁷Cs as a chronomarker) within one of the small catchments located in the basin of the upper reaches of the Medveditsa River. The noted dynamics in erosion intensity and suspended sediment yields took place against the background of a well-marked tendency (since the 1940s-1960s) of reduction in intra-annual unevenness of river water flow caused by a decrease in spring (snowmelt-induced, March-April) flood water flow, and by a more significant increase in water discharges during low-water-flow periods of year (winter (December-to-February) and river-ice-free period (mid-April-to-November)). These changes were accompanied by an increase in duration of spring (snowmelt-induced) flood flow with a reduction in its intensity, year-to-year anomalousness and contribution to total annual water flow of the rivers. The main reasons for all the changes noted over the last decades were climate change (a decrease in depth of soil freezing during snowmelt period caused by an increase in air temperature mainly in winter and spring months; an increase in winter thaws frequency) and human activity changes (mainly a reduction in cultivated land area, especially in the 1990s and early 2000s). The similar tendencies were identified over the last decades in other regions of the forest (south part), forest-steppe and steppe landscape zones of the East European Plain.

Keywords: Caesium-137; East European Plain; Flood; Sedimentation; Small catchment; Snowmelt runoff; Soil erosion; Soil freezing.