THE USE OF KETTLE HOLES FOR RECONSTRUCTING FORMER SOIL COVER IN DIFFERENT TYPES OF LAND USE Bogus ł awa Kruczkowska

The aim of the study was to identify and examine main directions of soil patterns, typology, SOC (Soil Organic Carbon) and Nt (Total Nitrogen) content in the topsoil changes that have occurred in kettle holes as an effect of soil erosion and anthropogenic denudation. Varied in the type of land use, three closed basins located in young glacial landscape in north-western Poland were investigated. According to the type of land use, the total area of soils with untransformed or moderately transformed morphology is different. Significant modifications have been taking place not only in mineral soils, which are located on slopes, but especially in soils of the bottom of sedimentary basins. In fact, most of primary soil properties and morphology have been replaced by new characteristics. The most intensive modifications of soil morphology and soil chemical properties occurs within croplands. Total area of colluvial soils can be treated as indicator of soil erosion processes intensity.


Introduction
Closed basins are numerous, but particularly small land forms, which occur mainly within young glacial landscape not only in Poland.The contemporary soil cover of closed basins in north-western Poland formed in the course of pedological processes after the last melting of the ice sheet in the Late Pleistocene period, within the range of the Pomeranian phase of the last Weischselian/Würm glaciation.
The term 'former soil cover' refers to soils which were developed completely after the last glaciation in Poland and non-transformed or slightly transformed by anthropogenic factors.In fact it is difficult to find natural soils, in view of pervasive human impact.Additionally the former soils should be developed from parent material, which had never been converted by soil-forming processes.It is almost impossible to recognize, because glacial deposits could be partly pediments.After Geographia Polonica 2016, 89, 3, pp. 323-343 the onset of human activity, soils were transformed, especially in undulated landscapes.To understand the relationships between soils and past slope processes, it is necessary to conduct paleopedologic research, which serves to reconstruct past environments (Karasiewicz et al. 2014;Mendyk et al. 2015).In agricultural lands, long-term tillage and strong natural slope processes cause runoff and infilling of depressions with sediments.An originally superficial soil profile is buried under deposited material.The properties of these new layers are related to the characteristics of the soils located upslope (Świtoniak 2015).Soil redistribution by tillage also modifies landscape topography (e.g.De Alba et al. 2004;Van Oost et al. 2005;Li et al. 2009;Vieira & Dabney 2011;Su et al. 2012;Rodzik et al. 2014).Knowledge of past events and current agricultural landscapes makes it possible to prevent their further degradation and peneplanation of Quaternary landscapes.Slope evolution is related to the duration of tillage, technological conditions, soil texture and morphometry of slopes.Previous studies of soil redistribution and modifications of geomorphology as a result of tillage (Lindstrom et al. 1992;Govers et al. 1994;De Alba et al. 2004;Świtoniak et al. 2016) confirm peneplanation of undulated agricultural areas.For this reason, closed basins are especially endangered land forms.Contemporary research proves that high soil redistribution is characteristic not only of modern tillage.Old cultivation methods, particularly at the beginning of human agricultural activity, were invasive and protective measures were not taken into account; therefore, the highest soil losses in the area investigated in the present study are characteristic of the past rather than the present.This phenomenon has also been confirmed in other studies (Quine et al. 1999;Thapa et al. 1999).
Closed basins are characterized by specific conditions of water circulation.To identify the basic types of kettle holes, a division proposed by Drwal (1975) was used.It is based on differences in the water cycle mechanism caused by the geological structure and distinguishes closed evapotranspiration basins and closed absorptive ones.The kettle holes examined in the present study represented the first type.The catchments of closed evapotranspiration basins are generally concave landforms without surface runoff with kettle ponds in the bottom (Major 2008).These specific land forms are numerous in young glacial landscapes around the world (Frielinghaus & Vahrson 1998;Kochanowska et al. 1998;Nichol 2001;Gaudig et al. 2006;Gerke et al. 2010;Corti et al. 2012), which makes them a universal tool for environmental reconstructions not only in Poland.
While we possess considerable knowledge about soil erosion and anthropogenic denudation, these processes have rarely been studied in relation to closed basins and submoraine depressions by Sinkiewicz (1998), Piaścik et al. (2001), Orzechowski et al. (2004), Sowiński et al. (2004), Lemkowska and Sowiński (2009), Sowiński andLemkowska (2009, 2010) and Major (2010).Most studies focusing on large areas have concerned geomorphology and history of their evolution.Comprehensive study of the processes occurring within sedimentary basins enables their identification on a local scale.The reason for undertaking the present study of kettle holes was insufficient characterization of soil erosion and anthropogenic denudation within objects with closed water circulation and of transformations of soil morphology resulting from these processes.
The aim of the study was to identify and examine soil typology changes that have occurred in kettle holes as an effect of natural (soil erosion) and anthropogenic (anthropogenic denudation) processes.Transformations of the former soil cover created as a result of listed phenomenons can be irreversibly saved especially in soil morphology and basic physical properties.It indicates the perfect soil memory.Based on Targulian's and Goryachkin's (2004Goryachkin's ( , 2011) ) observations, soil memory is 'in situ' by nature, which makes it the perfect tool for reconstructions on a local scale.Furthermore, soil as a complex unconsolidated mixture of inorganic, organic and living material is characterized by unique properties which are much more useful for landscape restorations than information included in sediments.Soils located within closed basins are preserved to different degrees, but all variations of soil properties reflect the influence of natural and anthropogenic processes.

Materials and methods
The study was conducted in 2011 in three kettle holes located in a young glacial landscape within a morainic plateau near Czaplinek (Fig. 1).The study area is located within the Drawsko Lakeland, which is a part of the West Pomeranian Lakeland in north-western Poland.The kettle holes are characterized by various degrees of slope inclination, ranging from 13° to more than 35°, with relatively flat bottoms (0-2°).The stand Drawsko with a catchment area of 20.4 ha is used as a forest (Galio-Fagetum), Siemczyno I (catchment area of 5.8 ha) comprises a grassland (plant communities of Arrhenatherion with dominant Arrhenatherum elatius) with a small area of a crop field and a spruce forest (Picea abies) with single specimens of Betula pendula, while Siemczyno II (catchment area of 6.5 ha) covers with a crop field with grassland (Magnocaricion) in the bottom of the closed basin.In the Drawsko closed basin, only the east part, with a total area of about 10.0 ha, was selected for detailed research.Based on historical maps: 1618 -E.Lubinus, Novo illustrissimi principatus Pomeraniae descrip-tis… (average map scale 1:227,000), 1789 -D.Gilly, Karte des Königl.Preuss.Herzogthum Vor-und Hinter-Pommern… (map scale 1:180,000), 1850 -G.D. Reymann, Topographische Specialkarte des Preussischen Staats und der angrenzenden Länder (map scale 1:200,000) and 1893 -Karte des Deutschen Reiches (map scale 1:100,000), it can be concluded that the soils at Drawsko was not tilled in the past and is, accordingly, relatively natural and furthermore Siemczyno II and partially Siemczyno I have been cultivated for at least 400 years ago.Nowadays in Siemczyno I only the west slope is still tilled.Animal-pulled tillage and human-powered hoes were the dominant farming system until about 20 years ago, what was identified from direct interviews with owners of surveyed fields.
The reconstruction of the former soil cover was based on investigations of morphology and grain size analysis of 200 cm deep soil profiles and 300 cm deep soil drillings.
In each of the sedimentary basins, transects were made, generally in the N-S and E-W direction.The total number of soil profiles collected was 43 (6 to 8 soil profiles per transect) -Figure 1.The profiles represent both mineral and organic soils from every part of the slopes.The study area is relatively lithologically homogeneous, covered by glacial and fluvioglacial deposits, with a predominance of loamy sand, sandy, sandy loamy and loamy texture.The primary range of each soil type was reconstructed on the basis of data obtained from soil profiles and auger holes drilled to a depth of 3 m.
The soils were documented and sampled in a standard manner (FAO 2006).Soils were classified according to the WRB soil classification system (2015).Texture was determined by combined sieve and Bouyoucos (1951) hydrometer method.Organic carbon (SOC) content was measured by wet dichromate oxidation method, and total nitrogen (N t ) content by Kjeldahl method.Uncalibrated radiocarbon dating of soil samples was made at Poznan Radiocarbon Laboratory.Statistical analysis were made using SPSS Statistics 17.0.

Transformations of soil cover at Drawsko (forest)
Compared with the reconstructions of former soils condition, present-day soil cover in the Drawsko sedimentary basin is more varied.Post-agricultural features are not present in the soils.For this reason the possibility of agricultural anthropogenic impact on soil cover formation in the Drawsko closed basin should be excluded.In spite of the effects of soil transforming factors such as erosion and other slope processes, undulated landscape and steep slopes, the contemporary soil profiles are practically natural (Fig. 2).The most transformations have occurred in the bottom of the Drawsko study area and they are connected with overdrying.Protection is primarily afforded by vegetation, which reduces the kinetic energy of precipitation and prevents rainwater from impacting on the sedimentary basin surface with the force which it exerts on exposed places.
The percentage of mineral soils in the original soil cover of both the slopes and the bottom was significant (about 90%).The main organic soil type in the lowest part of the basin was Fibric Histosols.From derivative Gleyic Luvisols (Loamic, Cutanic, Novic) features (ferrugineous mottling), it can be concluded that ground water levels in the past were higher than nowadays.The range of occurrence of these features in mineral soils in the sedimentary basin bottom leads to the conclusion that present-day groundwater levels are lower than in the past by up to about 50 cm.These significant fluctuations caused overdrying of superficial organic soil horizons, accelerating muck formation and their mineralization.The surface horizon of Hemic Drainic Histosols is built from loamy sand mineral material.As a result of water level lowering, organic layers composed of Fibric Soil Materials were transformed into Sapric and Hemic, which differ mainly in the degree of peat decomposition (peat, mucky peat, muck) and water content.These transformations resulted from natural processes without a direct anthropogenic impact on the soil such as drainage or agricultural drainage.The main anthropogenic alternation behind ground water level lowering in the lowest parts of the Drawsko study area was deforestation of the surrounding areas.Organic material is also observed at the surface of Gleyic Luvisols, which means that peat was also formed after mineral soil formation in the bottom of the sedimentary basin.
The gradual transformation of buried soils as a result of soil erosion led to a reduction or inhibition of primary soil-forming processes and the formation of Haplic Umbrisols (Colluvic, Raptic).Even though slope gradients were about 6-25°, the intensity of sediment transport down the slopes must have been slight.There were no mineral sediments on the surface of all organic soils examined in the area.Colluvial deposits up to 10 cm thick were observed only locally in the area immediately adjacent to the slope bases.In the N-SW transect, certain morphological changes were observed in the top profiles.Humus horizons divided into two sub-horizons were of considerable thickness (60-65 cm).Probably during the construction of a forest road the mineral material which was deposited along the edge of the Drawsko study area was mechanically translocated.Colluvial horizon thickness of mineral soil profiles on the north slope is 9-35 cm, but on the east slope it reaches 20-75 cm.

Transformations of soil cover at Siemczyno I (meadow)
On the basis of aforementioned historical maps analysis, the closed basin at Siemczyno I has been tilled for at least 400 years, but most of the study area is not cultivated at present.Only the west part of the study area is used for agricultural purposes.The remaining area comprises a meadow and a small stretch of a spruce forest on the north slope.In relation to the current condition, the potential primeval soil cover of the Siemczyno I closed basin was characterized by significantly lower typological diversity and increased ranges of certain soil types (Fig. 3).
The central part of the study area, as in the Drawsko sedimentary basin, was occupied by a water reservoir supplied with groundwater and originally with water melted from dead ice blocks deposited during ice sheet deglaciation in the Late Pleistocene.As a result of human settlement and intensification of tillage after the Roman period, the environment (including soils) was transformed Eroded sediments overlie the primaeval soil units located at the border between the slopes and the bottom of the basin without outlets.The thickness of allochthonous colluvial material in Haplic Umbrisols (Loamic, Colluvic, Raptic) which are located at the base of the slopes in the study area is about 65-90 cm.Despite the presence of slope sediments, significant soil loss is not observed in the higher parts of the slopes.It is difficult to state clearly what is the origin of these deposits and which factors (natural or anthropogenic) contributed to this redistribution.

Transformations of soil cover at Siemczyno II (arable land)
Modifications of soil morphology in the Siemczyno II sedimentary basin are observed in almost all soil profiles studied (Fig. 5).This area has been tilled integrally for at least 400 years and for this reason it is especially subjected to degradation and erosion processes.Using soil sample radiocarbon dating, it has been estimated that the most intensive slope processes in the Siemczyno II sedimentary basin took place during the Middle Ages (ca 560±30 BP; uncal.), which indicates the beginning of anthropogenic denudation.The superficial peat soil horizons in the bottom of the Siemczyno II closed basin were formed during the Subatlantic period (ca 2390±35 BP; uncal.).
Generally, this field is tilled twice a year (before sowing and after the harvest) to loosen the soil surface and mix the remaining organic material with soil.
A significant modification of Haplic Luvisol morphology is the complete absence of E horizons.The argic horizon was located directly under the humus horizon in all studied profiles.Morphological transformations of tilled soils are also visible on ortophotomaps.The contours of soils which are moderately modified are a darker color than non-transformed areas.These dark-grey units represent Haplic Luvisols (Aric, Cutanic), in which wetter Bt horizons are located directly under A horizons.This phenomenon is more noticeable in Siemczyno II than in Siemczyno I (Fig. 6).
Based on Świtoniak's division (2014), soils in the Siemczyno II study area are slightly and moderately transformed (Fig. 7).The modified soil units cover almost the total area of the closed basin.The range of colluvial soils is larger than in Siemczyno I or Drawsko.The most modified soils are located on the north and east slopes of Siemczyno II, which are 15-20 m high and their inclination varies between 3-25°.Changes of soil morphology on the remaining, 2-5 m high, slopes (south, west), with slope reduction about 0-5° are mostly the result of backfilling due to accumulation of material over the surface horizon.The thickness of the humus horizon increases from 25-30 cm at the highest points of slopes tops to 50-120 cm at the border between slopes and the bottom of sedimentary basin.Buried soil profiles are characterized by distinct transitions between further humus horizons, demonstrating their continuous agricultural use.Colluvial sediments, occurring at the base of north and south slope, provide protection against the impact of plowing for deeper soil horizons, which confirms the complete morphology of buried Brunic Arenosols at this location.The west part of the Siemczyno II study area is strongly modified by slope denudation, caused by soil erosion, anthropogenic denudation and cultivation machinery impact.At the surface of buried Fibric Histosols are 120 cm thick colluvial sediments.The period and type of tillage, which indicates the intensity of slope processes in Siemczyno II are the  Topsoil texture, SOC and N t content Depending on soil erosion intensity, these transformations may concern soil horizons located at different depths, however, the humus horizon is particularly exposed to this process.As a result of long-term cultivation, superficial horizons are transported down the slopes.Their redeposition is determined mainly by slope angle, plant cover, precipitation intensity and type of cultivation.The kettle holes in our study demonstrated some patterns of change in soil texture related to slope angle, which, however, were not statistically significant.Haplic Luvisols are the dominant soil type in the areas investigated in our study, which influences the distribution of soil texture.A moderate degree of erosion of these profiles with their former sequence of soil horizons leads to partial unveiling of the loamy Bt horizon and deposition of sandy material especially from the mixed A and E horizons at lower slope positions.Additional influence on the present condition of the soil cover, especially at the Siemczyno II stand, came from anthropogenic denudation, which led to the mixing of A and E material.Truncation of Haplic Luvisols is partially visible at the highest slope parts.On short slopes with a gradient of between 3° and 12°, translocation of sandy material is dominant (Tab.1).
Redistribution of SOC and N t along the line of the research transects is seen in zones located at the border between slopes and the bottom of the Drawsko, Siemczyno I and Siemczyno II study area.In the depositional landscape positions of the transects, concentration of these nutrients was higher than in the higher parts of the slopes by about 4.4-36.6g•kg -1 (Drawsko), 1.1-9.7 g•kg -1 (Siemczyno I), 0.1-45.0g•kg -1 (Siemczyno II) for SOC and 0.51-1.40g•kg -1 (Drawsko), 0.11-0.48g•kg -1 (Siemczyno I), 0.01 to 2.55 g•kg -1 (Siemczyno II) for N t (Tab.1).Concentrations of these nutrients within colluvial humus horizons were related to slope gradient, soil type, texture, flora and, as a result of combination of these factors, intensity of soil erosion.Differences in SOC and N t content between eroded and colluvial soils at Drawsko are not much marked.However, erosion contributes to translocation of small amounts of soil material and results in partial maintenance of natural terrain morphology and soil cover condition and is also visible in SOC and N t content in soil humus horizons.Colluvic Regosols are characterized by better chemical properties and greater solum thickness than eroded soils.Mixed soil horizons consisting of material derived from A and E horizons are much poorer in nutrients than soils with natural morphology.Generally, subsoil is characterized by low nutrient content,

Bogusława Kruczkowska
Geographia Polonica 2016, 89, 3, pp.323-343  Geographia Polonica 2016, 89, 3, pp. 323-343 an impact on the distribution of the biological activity index of soils.The C:N ratio of eroded and deposited A horizons at Siemczyno I was fairly uniform, varying from 10 to 15. Slight disproportions may result from the blurring of differences between soil properties of truncated and superstructure soils.Cessation of agricultural use and the development of a dense vegetation cover on the Siemczyno I slopes has resulted in neutralization of differences and is promoting homogenization of the superficial soil horizons.Disproportions are still strongly marked at the border between tilled and non-tilled soils, where the type of land use plays a key role in sediment and mineral distribution.The C:N ratio in colluvial A horizons at Siemczyno II ranged from 10 to 17, compared to 9-11 in eroded soils.

Discussion
The presence of closed basins in a young glacial landscape in north-western Poland has a significant impact on soil cover diversity.
The studied kettle holes were formed during the same period (about 12,000 years ago) as a result of slow melting of blocks of buried dead ice and have been subjected to similar processes.Despite these similarities, nowadays they are differently transformed.On the basis of previous research (Borówka 1992;Hulisz et al. 2012;Karasiewicz et al. 2014) in in relation to the former.The new soils have been developed by intense translocation and erosive effects due to manual tillage and land drainage.The part of the closed basin which is not used for agricultural purposes was probably tilled for a short time in the Middle Ages in view of its disadvantageous diversified relief.The intensification of tillage results in initiation of anthropogenic denudation and colluvial soil formation.The impact of tillage on soils in undulated landscapes is significant.In contrast to a common belief, strong soil translocation rates have been documented not only for modern tillage.Using animal power in land cultivation can also be dangerous, as it intensifies soil erosion and anthropogenic denudation.This phenomenon has also been confirmed by other researchers (e.g.Quine et al. 1999;Thapa et al. 1999;Turkenbloom et al. 1999).At Siemczyno I eroded sediments overlie the original soil units located at the border between the slopes and the bottom of the basin without outlets.It can be assumed that the presence of fully developed soil profiles in degradation areas is the result of strong, but monotonous slope processes, which are related to tillage or/and multiple redeposition of eroded material before its final accumulation within contact zone between slopes and kettle hole bottom.This phenomenon is also evidenced by Świtoniak (2011).In most colluvial covers, clear stratification is not observed, which further confirms this thesis.Significant changes in the near-surface soil properties depend on the length of the no-till period.Cessation of agricultural use results e.g. in better air conditions and increased soil porosity (VandenBygaart et al. 1999).
Long-term effects of soil erosion on slope profiles of closed basins are particularly significant in tilled areas, also at Siemczyno II.Tillage depth, direction and speed generally show considerable within-field variations (Van Muysen et al. 2006).The evolution of slopes and the rate of peneplanation of undulated areas in a young glacial landscape depend largely on human impact.Soil slope stability modifications due to soil erosion and accumulation processes can increase the risk of surface mass movement (Schumacher et al. 1999;Kosmas et al. 2001;De Alba et al. 2004).Tillage erosion smoothens the landscape and reduces slope angles by moving soil material (Van Oost et al. 2005;Zhang et al. 2008).The downslope direction of soil movement is characteristic of hoe and animal-power tillage.In mechanized agriculture areas, the soil is tilled in opposing directions, resulting in not only downslope soil deposition (Su et al. 2012).Soil variability of undulated areas changes according to tillage depth.The most noticeable alterations of soils are seen in the summit and toe positions.The impact of soil erosion and anthropogenic denudation is visible also in soil depth, which increases from the top to the slope base.Radiocarbon age of analyzed soil samples at Siemczyno II refers to results of palynological analysis of peat samples collected at Drawsko Lakeland by other researchers (Nita 2006;Lewandowski & Nita 2008).
Truncated profiles of Haplic Luvisols with the following sequence of soil genetic horizons: Ap-Bt-Ck, are commonly found in tilled areas of Poland (Sinkiewicz 1998;Szrejder 1998;Marcinek & Komisarek 2004;Stasik & Szafrański 2005;Kobierski 2013;Podlasiński 2013;Świtoniak 2014).That morphology is similar to Cambisols and therefore these type of soils are often confused with each other during field works (Świtoniak 2014; Świtoniak et al. 2016).Laboratory research reveals that topsoil horizons of Haplic Luvisols are built from a loamy sand soil material, while superficial horizons of Cambisols usually have a loamy texture, what is also confirmed at Siemczyno II.The stratification of allochthonous sediments at Siemczyno II is not clearly marked, which shows that their redeposition may have been the result of anthropogenic denudation (Paluszek 2010).Indirectly, it can also indicate a slow and long-term accumulation with the predominant influence of rill--wash or multiple sediment translocation before final deposition in the contact zone between slopes and the sedimentary basin bottom (De Ploey 1985;Smolska 2005).
Geographia Polonica 2016, 89, 3, pp. 323-343 Soil movement by tillage results in soil material displacement from convex slope positions and soil accumulation in concave slope positions (e.g.Govers et al. 1994;Lobb et al. 1995;Papiernik et al. 2007).Long-term tillage effects result in transformation of the mineral and organic soil profiles and the natural configuration of soil cover (Tsara et al. 2001).However transformations of organic soils are related not only to tillage, but also to groundwater level fluctuations.Tillage plays a significant role in soil redistribution on agricultural land (e.g.Frielinghaus & Vahrson 1998;Thapa et al. 1999;Van Muysen et al. 1999, 2000, 2006;Kosmas et al. 2001;Van Muysen & Govers 2002;Heckrath et al. 2005;Su et al. 2012).Anthropogenic denudation initiated by tillage leads to closed basin backfilling and contributes to the creation of colluvial sediment cover.Based on the range of allochthonous sediments it is possible to define the relative duration of tillage and intensity of the impact of the use of mechanical or/and animal power in land cultivation.It is also possible to make reconstructions of the original extent of sedimentary basins bottoms.Tillage erosion may be responsible for reductions of soil profiles (especially topsoil).Peneplanation of sedimentary basins causes reduction of geodiversity of young glacial landscapes.
According to our results, three main groups of transformation factors have a significant impact on soil cover condition: soil erosion, anthropogenic denudation and influence of groundwater level fluctuations.In combination with plant cover, soil texture, slope angle, precipitation and type of land use, these factors create unique conditions preventing or enhancing changes of soil cover.The intensity of their impact on soils was severe in the past but is highly limited nowadays.
Eroded soil mass movement determined by natural or anthropogenic factors is related to changes of soil texture (e.g.Chodak et al. 2005;Smolska 2008).Mahaney andSanmugadas (1989), Szpikowski (2003), Baužienė et al. (2008) and others have stated that soil material washed during erosion is fine--grained and well-sorted.However at studied kettle holes the movement of the sand fraction down the slopes is also observed.
Loss of SOC and total nitrogen is characteristic especially of tilled areas, which is related to the destruction of macroaggregates by soil material redeposition resulting from soil erosion.In well drained soils located within a wet footslope zone, the translocation of nutrients within the soil profile is more intense than in other parts of slopes (Gregorich et al. 1998).Soils located in upper slope parts have lower SOC and N t content than those at footslope positions, which is the result of loss of soil material, especially smaller and lighter particles enriched with nutrients (Lal 2004;Ritchie et al. 2007).This phenomenon also has an important influence on soil structure and texture of colluvial sediments (VandenBygaart 2001).Research results shows that SOC and N t concentration is observed in colluvial soils.A similar correlation has been confirmed by numerous studies (Gregorich et al. 1998;Lal 2003;Polyakov & Lal 2004;Zhang et al. 2006;Ritchie et al. 2007;Martinez et al. 2010).The relatively low C:N ratio of humus horizons of higher located soil units results from their rejuvenation (Baužienė et al. 2008).
Moreover, the landscape topography of closed basins determines the deposition of nearly all eroded soil material within their catchments.Insignificant or absent discharge of material enables complete reconstruction of past topography changes in basins without outlets and also sediment genesis with processes which they were subjected to.According to research data, mainly long-term conventional tillage practices in the past have a significant impact on soils in sedimentary basin bottoms.Disparities between contemporary mechanized and previous non-mechanized agriculture are significant and concern all soil properties.Despite appearances, the main backfilling period of sedimentary basins took place in the Middle Ages.Contemporary soil redistribution is initiated principally by water erosion and less by anthropogenic denudation.
Soil erosion proceeds at various rates, depending, among others, on soil texture.
Despite the presence of steep slopes (slope angles greater than 20°), a dense vegetation cover is a factor which inhibits runoff and soil material deposition.A good condition of today's closed basins results from appropriate agricultural practices and high resistance of cultivated soils to erosion.Steep slope parts are the most transformed and microrelief plays an important role in the process of soil material redeposition.

Conclusions
The modifications of contemporary soil cover in the kettle holes investigated in this study can be regarded as moderate.The type of land use intensifies or inhibits erosion and is, therefore, a main factor of superficial soil horizon transformations, what is visible on all studied kettle holes.Most soil cover changes, especially the formation of thick colluvial horizons, took place in the Middle Ages as a result of improper agricultural purposes.The type of land use strongly diversifies the intensity of soil cover modeling.Differences between the kind of modifications in particular research areas are significant and concern the range of colluvial sediments, overdrying of organic soils and initiation of new soil-forming processes.Changes of the former soil cover of closed basins are inevitable and strongly related to the type of land use.Preservation of the original sequence of genetic horizons in each type of soils is rare in the natural environment.The degree of transformation in soil morphology is an indicator of slope processes resulting from natural and anthropogenic events.No-till areas are characterized by the presence of a colluvial material cover created as a result of natural processes.These objects are moderately transformed, preserving a percentage of natural soils.Characteristic of tilled areas, besides thick allochthonous sediments, are distinct transitions between genetic horizons and soil compaction.The effects of human influence on soils are clearly visible, even long after cessation of tillage.The impact of soil erosion on soil cover in sedimentary basins is dependent on land use, agricultural practices, coverage by vegetation, slope angle, intensity of rainfall and soil moisture.The thickness of colluvial soils is diversified and depends on the intensity of soil erosion and anthropogenic denudation.In many cases, buried peat soils occur in their floor, indicating the extent of the former sedimentary basin bottoms.Shrinking of the area occupied by organic soils, an integral feature of post--glacial areas, significantly impoverishes soil cover diversity in hummocky young glacial landscapes.Patterns of SOC and N t translocation in individual types of land use are similar and confirm that the translocation of these nutrients is directed downslope.

Figure 1 .
Figure 1.The study area: A -Localization, B -Location of soil profiles within research transects

Figure 5 .
Figure 5. Siemczyno II soil cover: A -former (reconstruction at the base of terrain research), B -contemporary (according to IUSS Working Group WRB 2015)

Figure 7 .
Figure 7. Degree of soil profile truncation at Siemczyno II study area, according to Świtoniak's division (2014)

Figure 10 .Figure 11 .
Figure10.Chart of relationships between SOC (g•kg -1 ) content, location on the slope and type of land use