water Article Land-Use/-Cover Changes and Their Effect on Soil Erosion and River Suspended Sediment Load in Different Landscape Zones of European Russia during 1970–2017 Artyom V. Gusarov 1,2 1 Institute of Geology and Petroleum Technologies, Kazan Federal University, Kremlyovskaya Str. 18, 420008 Kazan, Russia; [email protected] 2 Federal and Regional Centre for Aerospace and Ground Monitoring of Objects and Natural Resources, Belgorod State National Research University, Pobedy Str. 85, 308015 Belgorod, Russia Abstract: Contemporary trends in cultivated land and their influence on soil/gully erosion and river suspended sediment load were analyzed by various landscape zones within the most populated and agriculturally developed part of European Russia, covering 2,222,390 km2. Based on official statistics from the Russian Federation and the former Soviet Union, this study showed that after the collapse of the Soviet Union in 1991, there was a steady downward trend in cultivated land throughout the study region. From 1970–1987 to 2005–2017, the region lost about 39% of its croplands. Moreover, the most significant relative reduction in cultivated land was noted in the forest zone (south taiga, mixed and broadleaf forests) and the dry steppes and the semi-desert of the Caspian Lowland—about 53% and 65%, respectively. These territories are with climatically risky agriculture and less fertile soils. There was also a widespread reduction in agricultural machinery on croplands and livestock on pastures of the region. A decrease in soil/gully erosion rates over the past decades was also Citation: Gusarov, A.V. revealed based on state hydrological monitoring data on river suspended sediment load as one of the Land-Use/-Cover Changes and Their indicators of the temporal variability of erosion intensity in river basins and the published results of Effect on Soil Erosion and River Suspended Sediment Load in some field research in various parts of the studied landscape zones. The most significant reduction in Different Landscape Zones of the intensity of erosion and the load of river suspended sediment was found in European Russia’s European Russia during 1970–2017. forest-steppe zone. This was presumably due to a favorable combination of the above changes in Water 2021, 13, 1631. https:// land cover/use and climate change. doi.org/10.3390/w13121631 Keywords: cultivated land; abandoned land; agricultural machinery; livestock; climate change; soil Academic Editor: Achim A. Beylich freezing; snowmelt runoff; river basin; sediment yield; forest-steppe; East European Plain Received: 31 March 2021 Accepted: 8 June 2021 Published: 10 June 2021 1. Introduction The East European, or Russian, Plain is one of the most extensive plains of the Earth’s Publisher’s Note: MDPI stays neutral landmass and the largest natural geographic region of Europe. The latitudinal zonation with regard to jurisdictional claims in published maps and institutional affil- of natural landscapes and their human transformation are well manifested in this region. iations. For centuries, fertile soils (mainly chernozems and grey forest soils) in the plain have been intensively cultivated. The expansion of cultivated land was accompanied by significant deforestation in the southern subzone of the forest landscape zone and forest-steppe zone. From the end of the seventeenth century to 1914, the territory of modern European Russia lost almost a third of its natural forests [1]. There were noticeable changes in Copyright: © 2021 by the author. the depth of soil freezing, soil filtration properties, and in the ratio between surface and Licensee MDPI, Basel, Switzerland. underground water runoff from hillslopes during the snowmelt period, mainly March This article is an open access article distributed under the terms and and April, and the warm season, mostly May to October, as a consequence of cultivation conditions of the Creative Commons and deforestation [1]. All these changes resulted in partial siltation and warm-season Attribution (CC BY) license (https:// drying of the regional network of creeks and small rivers, lakes, and ponds, in changes creativecommons.org/licenses/by/ in river water flow regimes, in accelerating water erosion and aeolian processes within 4.0/). interfluves [1–5]. In the forest and forest-steppe landscape zones, the maximum soil losses Water 2021, 13, 1631. https://doi.org/10.3390/w13121631 https://www.mdpi.com/journal/water Water 2021, 13, x FOR PEER REVIEW 2 of 30 Water 2021, 13, 1631 2 of 30 forest and forest-steppe landscape zones, the maximum soil losses occurred after the occurredagrarian reform after the in agrarianthe Russian reform Empire in the in 1861 Russian [6]. EmpireAccording in 1861to [7], [6 the]. According densest network to [7], theof gullies densest was network formed of in gullies the forest-steppe was formed zone in the owing forest-steppe to agricultural zone owingactivities. to agricultural A decrease activities.in the natural A decrease fertility in of the soils natural and fertilitya sharp ofincrease soils and in athe sharp volume increase of erosion in the volume products, of erosionespecially products, suspended especially sediment, suspended in rivers sediment, have also in occurred rivers have over also the occurred last centuries over the[3–5,7– last centuries12]. The combination[3–5,7–12]. The of all combination these negative of all processes these negative resulted processes in a noticeable resulted in deterioration a noticeable deteriorationof European Russia’s of European natural Russia’s environment natural environmentboth in the Russian both in theEmpire Russian and Empirelater, in and the later,Union in of the Soviet Union Socialist of Soviet Republics, Socialist the Republics, USSR or the Soviet USSR Union or Soviet [1,3,4]. Union [1,3,4]. After the collapsecollapse ofof thethe USSRUSSR inin 1991,1991, significantsignificant degradationdegradation ofof agricultureagriculture tooktook placeplace onon thethe plain plain within within the the modern modern Russian Russian Federation. Federation. It manifestedIt manifested itself itself mainly mainly in the in abandonmentthe abandonment of cultivated of cultivated land land (Figure (Figure1), reducing 1), reducing the fleetthe fleet of agricultural of agricultural machinery, machin- andery, and unprecedented unprecedented animal animal husbandry husbandry changes. changes. Regional Regional features features and and reasons reasons for for thethe noted changes in the post-Soviet space have been analyzed in numerous studies [[13–25].13–25]. ItIt isis alsoalso notednoted thatthat thethe practicepractice ofof cultivatedcultivated landland abandonmentabandonment in Europe as aa whole,whole, whichwhich beganbegan inin thethe 1950s,1950s, waswas mainlymainly owingowing toto technological,technological, socio-economic,socio-economic, political,political, demographic, andand climateclimate changeschanges [[26–33].26–33]. Figure 1.1. Change in the total area of cultivated land (F) inin thethe RussianRussian FederationFederation in 1970–2017.1970–2017. RSFSR—the Russian Soviet Federative Socialist Republic as the principalprincipal partpart ofof thethe formerformer USSRUSSR until December 1991; Fav—the average area of cultivated land; ∆F—relative change in Fav between until December 1991; F —the average area of cultivated land; DF—relative change in F be- 1970–1991 and 2005–2017av with p (Student’s t-test); R2—the coefficient of determination of a avsixth- tween 1970–1991 and 2005–2017 with p (Student’s t-test); R2—the coefficient of determination of a degree polynomial trend (1); 2—the years of the political and economic reform in the USSR, “Pere- sixth-degree polynomial trend (1); 2—the years of the political and economic reform in the USSR, stroika”. In the sixth-degree polynomial equation: Fi is the modeled F-value for the year yi. Note. “Perestroika”.According to the In thefive-year sixth-degree program polynomial for the develo equation:pmentF iofis the the socialist modeled plannedF-value economy for the year of the yi. Note.formerAccording USSR, the to total the five-year area of cultivated program for land the during development every five of the years socialist (…1971–1975, planned economy 1976–1980, of the1981–1985, former USSR,and 1986–1990) the total area remained of cultivated slightly land changed. during every five years ( ... 1971–1975, 1976–1980, 1981–1985, and 1986–1990) remained slightly changed. Despite the apparent progress in these studies, there is still insufficient research on the environmentalDespite the apparent impacts progress of land-use/-cover in these studies, changes there in is European still insufficient Russia research in recent on dec- the environmentalades. In particular, impacts this ofconcerns land-use/-cover the assessmen changest of inmodern European trends Russia in the in intensity recent decades. of soil In(i.e., particular, sheet and this rill) concerns and gully the erosion. assessment Centur ofies modern and even trends decades in the ago, intensity as mentioned of soil (i.e.,ear- sheetlier, erosion and rill) was and a severe gully erosion. problem Centuries in the region and. evenIt determined decadesago, the ecological as mentioned state earlier, of the erosionsoil and was surface a severe water problem bodies inand the was region. also Iton determinede of the factors the ecologicalaffecting food/environmental state of the soil and surfacesafety in water European bodies Russia. and was It alsois also one importan of the factorst to