Abstract. This article presents results from the long term-monitoring of gully headcut retreat rates (GHRR) between 1959 and 2015 in different parts of the Udmurt Republic and is based on the use of historical aerial photographs and field observations (measuring the distance from the gully head to a fixed reference point) ( Vanmaercke et al., 2016). It was determined that GHRR decreased from 2.4 to 0.3 m yr −1 during the 1959-1997 observation period and the 1998-2015 period, respectively. Measurements of GHRR were made once per year for most of the monitoring sites, and twice per year (after snow-melt in May, and after the rainy season, OctoberNovember) for gullies located in the eastern part of the study area that contain high proportions of arable land. 80 % of GHRR occurred during the snowmelt period (1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997), and decreased to 53 % since 1997. Spatial patterns of GHRR resulting from changing hydro-climatic factors for different regions of the Udmurt Republic, as a whole, were determined based on the analysis of long-term observations at 6 meteorological stations and 4 gauging stations. The main reason for decreasing GHRR appears to be due to reductions in winter frozen soil depth. The influence of stormwater runoff more clearly occurred within the east and north parts of the VyatkaKama interfluve, whereas higher correlations between GHRR and frozen soil depth were found for the western parts of the Republic. The most significant increases in GHRR appear to have occurred during the warm part of the year (June-July), after > 40 mm rainstorms.
For the first time, contemporary trends in water discharge, suspended sediment load, and the intensity of overall erosion in the river basins of the North Caucasus region, as one of Russia’s most agriculturally developed geographic areas, were identified. The study was carried out using monitoring data of the Federal Service for Hydrometeorology and Environmental Monitoring of the country for 21 rivers by comparing two periods: 1963–1980 and 2008–2017. According to the study’s results, trends of an increase in the mean annual water discharge (by 2–97%) and the essential reduction in its intra-annual variability have been found in most of the studied rivers. On the contrary, the trends of reduction in annual suspended sediment load and the intensity of erosion in the river basins were identified in most of the study region. Their most essential and statistically significant decreases (by 47–94%) were recorded within the Stavropol Upland, which several decades ago was considered one of the most erosion-dangerous territories of the entire country, as well as in some river basins of the central part of the Greater Caucasus’s northern slope (by 17–94%). The changes in climate (reducing the depth of soil freezing and meltwater runoff on the soil) and land use/cover (reduction of acreage and load (pressure) of agricultural machinery on the soil, reducing livestock on pastures, and the transfer of water from the neighboring, more full-flowing rivers) are considered the leading causes of the aforementioned trends. The findings will contribute to solving some economic and environmental problems of both the region and adjacent territories and water areas.
This paper is devoted to revealing and estimating the contemporary soil erosion rates trend within arable lands in the south of the forest zone of European Russia, based on the study of sedimentation rates at a small dry valley bottom with almost completely cultivated catchment slopes. The dry valley catchment (0.68 km2) is located in the south part of the Udmurt Republic (the mixed forests zone) within the Izh River basin. The bomb-derived and Chernobyl-derived radiocaesium–137 was used for dating valley bottom sediments in two time intervals: 1954(1963)–1986 and 1986–2016. To analyze the causes of change in sediment redistribution rates, morphological and morphometric analyzes of the valley, the results of year-to-year observations for gully heads retreat in the catchment vicinities, hydrometeorological observations of the Russian Hydrometeorological Survey network, and also aero- and satellite images across years were used. There was a noticeable decrease in the sedimentation rates of washed-out soil material from the catchment slopes at the valley bottom over the past 60 years: from 1.8–2.5 cm/year during 1954–1986 to 0.15–0.75 cm/year for 1986–2016. Hence, the sedimentation rates have decreased by 2.5–3 times as a minimum. This trend is consistent with a decline of the average retreat rates of gully headcuts within cultivated lands in the Udmurt Republic over the past 40 years — from 1.3 m/year in 1978–1997 to 0.3 m/year in 1998–2014. We suppose that the main reason for such significant reduction of erosion rates was a increase in protective crop coefficient associated with a increase in the proportion of perennial grasses since the late 1980s. Additional contribution to the erosion reduction was owing to a decrease in surface snowmelt water runoff within the catchment area since the early 2000s, associated with the reduction in soil freezing depth and general increase in air temperature during the winter and spring months in this region of the Russian Plain.
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