Impact of Land Use Changes on Collapsed Pipes Development in the Loess Gully (Lublin Upland, East Poland)

The collapsed drainage channel of this catchment, with several pot holes in the bottom, cuts the edge, the waterlogged arm of the northern gully. The local relief between the bottom of the gully and the top is less than 20 m. Gully is about 10 m deep. The upper part of the gully has been transformed by a terrace at forest edge. The youngest border, located at the highest point, directs runoff along the edge of the gully (Fig. 3).

Fig. 3.

Cross-section of modern forest edge (A), with truncated and overlying Luvisol profile (B): and contact of loess sinkhole wall with fill deposits (C) and silted channel (D). pc – ploughing colluvia, bl – basal loess, fc – falling colluvia, fp – fossil pipe.

The western wall exposed a soil profile of a typical Luvisol (Fig. 3A), cut by plowing (Fig. 3B) at the low position of the forest edge, so possibly at a time not too far from the formation of the gully. The dissection of the edge forced it to move up the slope. In the resulting sinkhole, there was a sediment accumulation, originating from the outcrop – packets of different soil horizons. The vertical contact between the loess wall of the sinkhole and the infilling sediments, whose consolidation indicates an advanced age, is evident (Fig. 3C). This took place with infiltrating water, as evidenced by the laminated filling of a small channel (Fig. 3D). Reactivation of the modern sinkhole began along the western wall of its predecessor on contact with fill deposits, which were gradually removed (Fig. 4A). However, erosion did not reach the eastern wall, leaving much of the infilling sediments (Fig. 4B, C, D).

Fig. 4.

Dissection of the forest edge under the chokeberry plantation (A) and exposures of sediments infilling the old sinkhole (B, C, D): ac – water colluvia, fc – falling colluvia, pc – ploughing colluvia.

These sediments, exposed in two profiles, document the reclamation process of this sinkhole. In the profile on the line of the forest edge, three types of colluvial sediments were distinguished (Fig. 4C, D). Above the lower one-meter-long inaccessible section, located in the sinkhole, there are horizontally layered water-deposited sediments from the dilution of various soil horizons with a total thickness of 1.25 meters. They document the silting up of the sinkhole after closure of the channel outflow. On top of the layered sediments lies a half-meter series of deformed packets and lumps of various soil horizons. The textural features of the sediment, especially its partial mixing, may be traces of shrub clearance, overgrowing the edges of the sinkhole. Subsequently, tillage erosion caused deposition of soil into the centre of the pit, gradually made it shallower. Vegetables, especially cabbage, were grown in the reclaimed depressions due to the greater soil moisture content (Rogoza 2005 – oral information). Based on the interviews, it was assumed that agricultural use of the collapsed pipe, equivalent to its reclamation, took place between 1940 and 1995, so the rate of deposition of agricultural colluvium at the forest edge was about 4 cm per year. This is several times higher than the amount of annual deposition in the closed depressions (Rejman et al. 2014, Rodzik et al. 2014, kołodyńska-Gawrysiak et al. 2018). In contrast, agricultural terraces, which similarly function as denudation bases on slopes, are growing at a similar rate (Ziemnicki 1968).

This sinkhole is the main part of the complex system with several secondary forms, active even during the stabilization phase (Fig. 5A). In the exceptionally quiet year of 2007, in terms of erosional processes, only one channel, draining the new western sinkhole in the complex, was reported to be discharging sediments throughout the catchment. The Site 1 complex continues to develop, especially in wet years with abundant rainfall runoff. The western collapsed pipes, in particular, is active, taking in runoff from two longitudinal fields. The change in the direction of cultivation to perpendicular to slope, which was made after the removal of the chokeberry and currant plantations, should limit its development.

Fig. 5.

Development of the secondary collapsed pipe at Site 1: A – view of the collapsed pipe catchment. B – recent edge of the collapsed pipe on the agricultural terrace (white dotted line).

The collapsed pipe, in terms of its location, size, time and conditions of development, is similar to the one discussed above. A collapsed drainage channel cuts the edge of the southern gully, overlain by colluvial sediments accumulated in a zone of two different ages of field-forest boundaries (Fig. 6). The collapsed pipe itself was cut into an agricultural terrace. located in the shallow depression and formed by the deposition of colluvial sediments (0.80–1.45 m thick).

Fig. 6.

Development of the collapsed pipe at Site 2, A – in 2004. B – in 2024. red arrow – erosion furrow. 1 – forest edge, 1a – contemporary, 1b – former, 2 – direction of tillage, 3 – direction of surface runoff, 4 – ploughed erosion rills; 5 – colluvial fan, 6 – sinkhole, 7 – collapsed pipe, 8 – reclaimed pipe. DEM from 2022 (Główny Urząd Geodezji i Kartografii. 2024. LiDAR. Access November 2024. https://www.geoportal.gov.pl/).

Beneath these sediments, the walls of the collapsed pipe have preserved a Luvisol, generally with a complete profile, with the upper levels somewhat transformed by cultivation (Fig. 7A). The collapsed pipe is active and drains sediments through a drainage channel with pipes. At its outlet, a classic depositional cone has developed in the bottom of the gully (Fig. 7B). The remains of a possible older collapsed pipe were not found, despite the fact that two forest edges were found older and younger. Instead, they were found on the walls of a secondary form that develop on a path on the slope of the gully. This path intentionally collected runoff, directly into the gully, to limit the development of the upper collapsed pipe. At the former forest edge, a new collapsed pipe was quickly formed, with characteristic rills cut into the vertical walls built in part from in situ loess and in part from colluvial packets, mostly without soil material (Fig. 9).

Fig. 7.

The collapsed pipe at site 1: A – Luvisol and agricultural colluvia on the collapsed pipe wall. B – drainage channel with pipes and depositional cone at the outlet.

Fig. 8.

The secondary collapsed pipe at Site 2: A – front loess wall with pipe, B – side wall with colluvial fill, C – drainage channel.

Fig. 9.

Changes in the development conditions of the Site 3: A – state before 1980. B – present state. 1 – forest edge, 1a – contemporary, 1b – former, 2 – direction of tillage, 3 – direction of surface runoff, 4 – ploughed erosion rills; 5 – colluvial fan, 6 – sinkhole, 7 – collapsed pipe, 8 – reclaimed pipe. DEM from 2022 (Główny Urząd Geodezji i kartografii. 2024. LiDAR. Access November 2024. https://www.geoportal.gov.pl/)

The third studied collapsed pipe, the largest in the entire gully system, is located on the slope of the southern gully (Fig. 2). It is the result of dissection of the slope of gully, predisposed by agricultural use. Initially, it was a linear dissection, and over time other processes shaped it: headcut erosion in the head section and piping, mainly shaping the drainage zone. Although it originated and developed at the same time as the previous two, favourable conditions for its development occurred much earlier, when, around 1980, the cultivation of the extensive field from which runoff flows into the collapsed pipe was diverted (Fig. 9).

The shifting of the forest edge also took place in the case of this collapsed pipe. As late as the mid-1960s, the entire slope and bottom of the gully was used for agriculture at the cross-stream. The gully was abandoned around 1970, marking the forest edge on its natural edge, obliterated somewhat by agricultural cultivation. However, after the cultivation direction was changed to longitudinal, it became susceptible to piping (Fig. 10). Consequently, the boundary was moved to the slope of the plateau, which reduced the threat for a while.

Fig. 10.

Pipe filled up with sediments at the intermediate forest edge.

At the same time, the method and type of cultivation that promotes piping and approximates this hazard was practiced. Growing currant in longitudinal rows generates and concentrates lots of surface runoff (Fig. 11A). Once a plantation begins to bear fruit, it can be kept in turf, which largely prevents flushing (sheet and rill erosion). However, in this case, currant seedlings were grown for several years in a row. Such cultivation leaves the soil in herbicide fallow, thus generating runoff in every season, concentrated in the corner of the field. This resulted in the rapid development of a single collapsed pipe (Figs 11B, 12), whose volume approaches 1000 m³.

Fig. 11.

Pattern of runoff along the recent forest edge on the agricultural terrace (A) and severe piping on the slope of the gully (B).

At the end of the modern erosional period, two phases of piping activity can be distinguished (Fig. 12). One, from the late nineteenth and early twentieth centuries, was associated with the parcelling out of part of the Celejów estate, the fragmentation of manorial land and changes in the pattern of fields (Kowalik-Bodzak 1964). The second, contemporary, a century later, is associated with berry bush plantations and cabbage cultivation (Rodzik, Zgłobicki 2000. Rodzik et al. 2009. Zgłobicki 2002). The development of three representative collapsed pipes demonstrates the spatial-temporal complexity of the transformation of these forms (Table 1), occurring under the influence of not only indirect, but also direct, intentional human intervention (Fig. 13).

Fig. 12.

Dynamic development of the single Site 3 collapsed pipe: A – 2012, B – 2013, C – 2015, D – 2022.

Fig. 13.

Development phases of the Site 1 collapsed pipe: A – dissection of the young gully escarpment in axis of depression. B – development of the large collapsed pipe on the line of concentrated runoff after the change of cultivation direction. C – relocation of the forest edge and reclamation of the collapsed pipe. D – reactivation of the collapsed pipe under the chokeberry plantation. E – the beginning of the development of secondary collapsed pipes during the period of stabilization, F – Intensive development of secondary forms during periods of higher rainfall. Explanations: 1 – contour lines, 2 – parcel borders, 3 – forest edge, 3a – current, 3b – former, 4 – direction of cultivation, 5 – direction of surface runoff, 6 – increased infiltration, 7 – sinkhole, 8 – collapsed pipe, 9 – piping channel, 9a – subsurface, 9b – open, 10 – colluvial fan, 11-colluvial filling of the reclaimed collapsed pipe.

The modern development of collapsed pipes was initiated by pronounced runoff after the long, cold and snowy winter of 1995/96. In the first days of April 1996, intense snowmelt triggered the development of numerous piping forms in the loess gullies of the western part of the Nałęczów Plateau (Gardziel, Rodzik 2005). In the gullies near Celejów, the effects of snowmelt were superimposed on the effects of heavy rainfall: in September 1997 and June 1999 (Zgłobicki 2002). The stages of contemporary collapsed pipes evolution are presented in the example of Site 1.The first few years of development (Fig. 13D), associated with frequent runoff, mainly from snowmelt, were followed by several years of stabilization of the forms (Fig. 13E), with low rainfall and retention in sodded plantations. In subsequent wet years, rainfall runoff was frequently recorded. Changing runoff from plantations to bypass existing collapsed pipes resulted in the development of secondary forms (Fig. 13F).

Our research confirmed that land use changes significantly affect soil piping through alteration in soil properties and surface and subsurface runoff (Table 2). Studies by Wilson et al. (2015) indicated that different land uses affect soil characteristics, intensive agriculture or pasture may increase the likelihood of pipe formation due to changes in soil structure and compaction. In particular, they emphasise the role of past land use, which has influenced changes in the morphology of the soil profiles and the formation of poorly permeable horizons. At the same time, research by Jones, Cottrell (2007) indicates that piping processes occur more frequently on agricultural land than in forests. The same conclusions were reached by Bernatek-Jakiel and Jakiel (2021) for areas located in the Bieszczady Mountains (Poland). In our case, intense piping developed at the forest edge, with form renewal often occurring at the boundary of in-situ loess and what colluvium fills the fossil sinkholes (Table 2). The way the land is used affects the volume of water flowing down the slope and can lead to the development of piping processes. Where there is a high hydraulic gradient near the edge of the gully, infiltration and piping develop.

Agriculture pressure on the gullies stopped in the 1970s, which had to do with the development of industry, providing employment – it was common to commute to work in city of Puławy. Access to building materials and fuel was easier. Gully channels were not needed for the passage of motor vehicles, and the plots of land located in them were not suitable for mechanized cultivation, so they were set aside. Agrotechnical services recommended the use of soil-stabilizing crops, such as orchard crops, which include fruit plantations. After the political transformation, since the 1990s, crops of brassicas and ornamental shrubs also appeared.

In the modern period, the layout of the manorial fields was dominated by extensive fields, oriented SSE–NNW, parallel to the southern gully. This field direction was preserved on the north-eastern edge of the catchment area (Fig. 2). It is likely that they stretched all the way to the present-day Kolonia Stok, crossing the dry valley, which, along with them, was soon cut by the northern gully. This is evidenced, among other things, by the distribution of bank gullies of this gully every 100 meters, formed on the borders of the fields (Fig. 2). Contributing to their development were roads running across the gully. The profiles of fossil Luvisol and the relationship of the field pattern and gullies indicate the diametrically opposed ages of the two main arms of the gully system. The southern one was formed in the Neolithic, while the northern one was formed in the period corresponding to the ascending phase of the Little Ice Age (Rodzik et al. 2014).

The edges of permanent gullies are particularly threatened by piping and headcut erosion as a result of concentrated surface runoff from agricultural fields. A large role is played by the stabilization of the forest edge, usually functioning over the edge of the gully (Maruszczak 1954, 1973). In this zone, cracks are formed as a result of tension and agrotechnical operations, promoting water infiltration and subsurface runoff. Between the maximum extent of tillage and the forest edge, abandoned grassland or shrubs buffer strips are formed. These buffer strips are characterized by intense biological activity of burrowing soil fauna, promoting subsurface runoff (Verachtert et al. 2013, Wilson et al. 2015, Poesen 2018, Hosseinalizadeh et al. 2023). Additionally, the gully slope determines steep local hydraulic gradients. As a result, sinkholes and collapsed pipes starting to develop in these locations (Rodzik et al. 2021, Kołodyńska-Gawrysiak et al. 2024). Piping associated with a steep hydraulic gradient is mainly observed in earth banks: agricultural terraces, lynchets, sunken lane banks and gully banks (Poesen 1989, 2018, Verachtert et al. 2011, Vanmaercke et al. 2021). It is often initiated by small animal holes (Verachtert et al. 2010, 2011). The formation of piping sinkholes several meters in size and with a volume of up to 100 m³, usually takes several years, but this can occur even during a single, intense snowmelt event. After some time, under the influence of changes in agricultural practices in the micro-catchment, the sinkholes and collapsed pipes may become not active, but remain “on standby” for further development under favourable conditions. The final stage of their development may be a blind valley, dissecting the edge of the gully or a bank gully (Gardziel et al. 1996. Rodzik, Zgłobicki 2000, Verachtert et al. 2010, 2011, Kołodyńska-Gawrysiak et al. 2024).

Piping processes thus contribute to the spatial development of gullies, especially during snowmelt (Gardziel, Rodzik 2005, Poesen et al. 2003, Vanmaercke et al. 2016). Episodic runoff outflows from animal channels usually do not exceed 1 dm³ s⁻¹, but are significantly saturated with suspended solids, up to 200 g dm⁻³ and more. This is favoured by thawing of the ground and gravitational processes (drop-off and liquefaction) on the pipe walls. Saturation with suspended sediments forces its deposition (usually on snow) at the slope drop-offs at the outlets of the passages in the gully bottom (Rodzik et al. 2009). The result is the relative stabilization of such a section of gully with a flat, accumulative bottom.

The stabilization of the bottom slopes was an incentive for owners of small farms to enlarge them by putting such a section of the gully under short-term cropland. This was preceded by hand clearing of trees and shrubs. This involved smoothing of the slopes by gravitational displacement of soil activated by tools. However, fields that were difficult to cultivate were soon turned into pastures and eventually into fallow land, subject to a secondary succession of Tilio-carpinetum forest with pioneer birch (Rodzik 2010). The loosening of the loess subsoil and poor consolidation of the infilled incisions from the first phase, created conditions for the re-development of sinkholes, collapsed pipes and channels, as exemplified by the three selected sites on the edges of the loess gully in the Kolonia Celejów on the Nałęczów Plateau.