INTRODUCTION

Soil formation on technogenic waste is widely studied in Russia and in the world. Special attention is paid to transformation of mineral waste of the mining and construction industries stored in dumps, tailings, and landfills. These objects are considered as models for studying the initial soil formation and plant successions in different natural zones, and the properties of soils on human-made waste of different compositions [1, 8, 55, 57].

Much less attention is paid to soil formation on dehydrated sediments of treatment facilities of industrial plants (paper, food, etc.), municipal enterprises, areas of activity of water canals, and other sources of wastewater sediment [5, 17, 18, 43]. A special place among these objects is occupied by treatment facilities of sugar factories. Sugar production is one of the oldest food industries, and its enterprises in Russia are located in the areas of growing its raw material—sugar beet. These are mainly forest-steppe and steppe zones with gray forest and chernozem soils. Relatively small enterprises are concentrated in the warmest areas of the southern taiga zone. A significant part of them—34 of 74 operating ones—are located in the central chernozemic region in the European part of Russia [51].

Sugar production needs significant amount of water [39], and the volumes of wastewater discharge from sugar factories are extremely large. Their purification requires complex technological techniques, one of which, despite modern methods, is still represented by special hydraulic constructions: sewage treatment ponds or infiltration fields (IFs) [17, 21, 40, 44].

They consist of a network of settling ponds, or checks, surrounded by earth walls with various technical elements built into them for wastewater supply and discharge. Mixed production waste may enter them in addition to wastewater in the form of suspensions: filtration sludge (defecate), mainly consisting of lime used in sugar production, conveyor-washing sludge, and organic material [39].

Infiltration fields (sewage treatment plants) at sugar factories occupy from 70 to 250 hectares. They form a typical local landscape with specific cellular pattern of relief and function under the impact of water regime determined by the sugar production technology, wastewater composition, and climatic conditions of the area.

The review of modern Russian and foreign published works shows that IFs of sugar factories are primarily studied from the environmental point of view, and soil formation on sewage sludge is beyond research interests [19, 20, 47]. However, there are works [26, 34], in which some soils of IFs of the L’gov sugar factory are identified without detailing, and the studies [40, 41] devoted to the analysis of the post-technological transformation of industrial landscapes of historical and operating sugar factories. The authors studied abandoned industrial sites of factory zones and identified soil and soil-like formations: industrizems, embriozems, technozems, replantozems, and ekranozems [40, 41]. However, the soil cover of treatment facilities was not studied, and the impact of sugar production waste on soil formation was not considered. Soil classification was not discussed in these works.

In this regard, there is an obvious need to study the complex of factors and processes of formation and transformation of soils under the impact of sugar industry, the relationships of technogenesis and natural processes, and the diversity of soils formed on various elements of IFs and under different modes of their functioning. The classification position of soils should be determined.

The purpose of this work is to identify the specificity and main regularities of soil formation on existing and abandoned IFs by the example of sugar factories in the forest-steppe zone of Kursk oblast.

OBJECTS AND METHODS

The objects of the study were represented by soils of IFs of sugar beet factories: the operating L’gov factory and the closed in the early 2000s Peny factory in Kurchatov district of Kursk oblast (Fig. 1). Typical virgin chernozem (migrational–mycellary) of the Kursk Biosphere Station with the AU–AUlc–VSAms–Cca horizons [46, 54], or Haplic Chernozem Pachic according to the WRB [52] was used as the background soil.

Fig. 1.
figure 1

Location of the research objects: 1—orthophotoplan of infiltration fields of the operating L’gov sugar factory; 2—orthophotoplan of infiltration fields of the closed Peny sugar factory.

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The area is located in the forest-steppe zone. The mean annual air temperature in the region has increased by 2°C on average over the past 10 years and is +7.8°C; the coldest month is January (–6.6°C), and the warmest month is July (+21.3°C). The mean duration of the growing season is 185 days. The mean annual precipitation is 570–600 mm [27]. Dominant soils are represented by typical chernozems on loess-like loams and are mainly plowed. Hydromorphic soils of various gleying are formed in small areas near local reservoirs, in floodplain depressions, and in flat depressions on watersheds under conditions of increased watering. They form a sequence from meadow-bog to chernozem-meadow (from mucky quasi-gley to humus quasi-gley) soils depending on the topographic position. The soils are enriched with organic matter and have a slightly acid or neutral reaction in the upper horizons and slightly alkaline reaction in deeper horizons [27, 36].

All the considered IFs were created in the 1950s [34].

The IFs of the operating L’gov sugar beet factory (of an area of 175 ha) are found on the watershed of the Byk and Opoka rivers, on Quaternary sediments underlain by marls. The width of checks varies from 30 to 80 m, and the length is from 60 to 300 m. The height of walls between the checks is 1.5–4 m, and the width is from 1.5 to 3 m.

The IFs of the closed Peny sugar beet factory (177 ha) are located on the second terrace of the Seim River. Their checks are from 50 to 80 m wide and from 160 to 290 m long and are surrounded by walls with a height of 2–4 m and a width of up to 2 m.

The analysis of the survey materials from unmanned aerial vehicles (UAV) shows that the bottoms of the checks are 3 to 40 m higher than the surrounding area. This ensures free drainage and prevents long-term water stagnation in them.

The relief of IFs of sugar factories is represented as a specific “cellular” or check-shaped morphosculpture (geomorphologic phenomenon). According to the shape, rectangular, polygonal, and parallelogram patterns are distinguished. This is clearly visible on the images obtained from the UAV.

Terrain studies were performed in 2019–2022. Data on soil pits are given in Table 1.

Table 1.   Brief data on soil pits (2019–2022)
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Six groups of soils formed on the walls and in the bottoms of checks were identified in the study area. Soils of the most typical locations were described in each group. They differed in the factors and specifics of pedogenesis. The morphology of soil profiles of IFs is shown in Fig. 2.

Fig. 2.
figure 2

Soil profiles at the bottoms of checks and on the walls of infiltration fields: (a) mucky–humus quasi-gley artistratified soil (pit LG-10-20, group II-1), (b) dark humus soil on artifimostrate (pit PN-03-21, group II-2), (c) mucky–dark-humus quasi-gley soil (pit LG-02-19, group II–3), (d) migrational–mycellary quasi-gley chernozem (pit LG-01–20, group II-4), (e) technogenic humus pelozem on artiindustrate (wall, pit LG-08-20, group I-2), and (f) dark-humus typical soil on organolithostrate (wall, pit LG-02-20, group I-1).

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Soils formed on check walls of IFs of the L’gov and Peny sugar factories. The walls have not undergone strong anthropogenic impact since their formation in the 1950s; some walls were locally damaged during the treatment of checks from sewage sludge and were used for unpermitted storage of construction and household waste.

Two types of walls with typical soils were identified:

(I-1) soils of walls composed of mixed material of initial soils (typical chernozems) and calcareous loess-like loams brought from IFs during their construction (Fig. 2f);

(I-2) soils of walls covered to a depth of more than 1 m by dehydrated sewage sludge (a mixture of lime defecate and organic material) transported from the checks during their treatment (Fig. 2e).

Soils formed in the bottoms of checks. The initial depth of checks was 2–3 m, and the lowest horizons of the original chernozems and carbonate loess-like loams were uncovered on their bottoms during excavation.

Four groups of soils in checks with different functioning regimes and the period after the stop of their use are identified:

(II-1) soils in the checks annually flooded with sewage for 2–3 months and gradually accumulating sewage sludge; when the waters are discharged, the sediment is partially washed out, and the surface dries up until the next flooding. The surface is covered by duckweed (Lemna minor) and mesophilic low grass during subsequent drying (Fig. 2a).

(II–2) soils in checks abandoned 20 years ago, untreated of dried sewage sediments under tall-grass plant cover composed of annuals (Fig. 2b);

(II-3) soils in checks abandoned 30 years ago and purified of sewage sludge with a temporary perched water table under common reed (Phragmites australis) (Fig. 2c). After the sediment was removed, the underlying material of abraded initial soils and loess-like loams altered under the impact of mineralized wastewater during the use of checks was uncovered.

(II-4) soils in checks abandoned 40 years ago and cleaned from sewage sludge under ash-leaved maple (Acer negundo) (Fig. 2d).

Abandoned checks may be temporarily flooded by rain and snowmelt waters.

Terrain studies included morphological description of soil pits (nine profiles) using Munsell color tables and determination of soil bulk density using Kachinskii’s auger (100 cm3 in volume) and penetration resistance by a penetrometer. We performed the hierarchical morphological analysis with application of mesomorphology in the field (detailed examination with a magnifying glass) and in laboratory (Leica MZ6 optical microscope, magnification of ×6–80) and micromorphology (study of thin sections using a Nikon E200 Pol polarization microscope at magnifications ×40, 100, and 400).

Physical, physicochemical, and chemical soil properties were determined at the Chemical Laboratory of the Institute of Geography of the Russian Academy of Sciences by standard methods: particle-size distribution by sedimentation (pipette) method with pyrophosphate pretreatment, pH by potentiometric method, and the content of carbonates by alkalimetric titration [2, 9, 10]. The carbon and nitrogen contents were measured on a Vario Isotope cube CHN analyzer (Elementar) using flow mass spectrometry after pyrolysis of the sample at 1500°C in the Laboratory of Radiocarbon Dating and Electron Microscopy of the Institute of Geography. The salt composition of soils was determined by an ICS-1100 ion chromatograph. Chemical composition of wastewater from the L’gov Sugar Factory sampled from the operating checks in the fall of 2020 and 2021 was studied using a 5110ICP-OES emission spectrometer with inductively coupled plasma and an ICS-1100 ion chromatograph.

The plant cover was characterized for the period of the description of soil pits. Its changes were recorded during repeated visits; they were especially well seen in the operating checks and were related to the period of their drying and overgrowing. We consider the described plant cover as one of the repeating stages with their own contribution to soil formation.

Various sources of spatial data were used for geoinformation support of pedogenetic studies. Survey data of UAVs DJI Mavic pro platinum and Mavic pro 2 (from different heights in the range of 100–200 m) and photogrammetric processing (Agisoft Metashape Professional Edition, Version 1.5) of these materials were used to construct digital models of topography with a spatial resolution of 6–12 cm and orthophotoplans with a spatial resolution of 3–6 cm. They were used as the basis for determining morphometric parameters of the relief, including elevation of IFs over the surrounding area as a factor preventing water stagnation and waterlogging. Interpretation of satellite images taken in different years allowed us to reconstruct the periods of using IFs of checks and the time of their decommissioning and abandonment.

Soil names are given according to the Classification and Diagnostics of Soils of Russia (2004) and the field correlation manual (2008) [23, 30] with amendments concerning classification elaboration [33], as well as according to the WRB system [52]. It should be pointed out that the specificity of soils of the studied IFs and the ratio between natural and technogenic processes and properties creates significant difficulties for correct correlation of soils according to the Russian classification, as well as for finding analogues in the international classification.

TECHNOGENESIS AS A SOIL-FORMING FACTOR

Disturbance of soils and rocks—mechanical transformation during the operation of machines—begins at the construction stage of IFs, when a network of checks separated by walls is created, and technical structures are introduced into the natural environment (Table 2). New positive and negative forms of topography are formed within the IFs of hundreds of hectares in area. Earth walls overgrown by dense grass cover or shrubs and trees (mainly by ash-leaved maple with a deep and branched root system) are more stable than walls composed of solid defecate. The latter becomes loose while drying and is eroded when moistened, which causes deformation of the surface and slopes. The plant cover on such walls is formed by annual tall grasses with participation of reed and ash-leaved maple. However, the material on the surface and slopes of walls is not fixed.

Table 2.   Technogenic geochemical and mechanical loads typical for infiltration fields of sugar factories at the stage of construction and operatio
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Infiltration fields operate in the mode of periodic filling with wastewater mixed with diluted filtrate (defecate) and conveyor-washing sediments and in the dewatering mode.

After the production is completed, the checks are partially or completely cleaned of the sediment and prepared for reuse, which causes significant mechanical disturbance of the bottom surface and sometimes of the wall slopes. Filtration properties and water permeability of abraded soil at the bottoms become poorer. Available data, including our own terrain studies, show that when these checks are not used for a long time, the abraded mineral horizons at the bottoms dry up and crack (especially strongly in case of a large content of calcareous defecate) and become similar to takyrs with the polygonal-fractured pattern of the surface [40]. According to the observations of the authors, annual plants from surrounding areas (for example, association Cannabio–Atriplicetum nitentis (Ishbirdin et al., 1988)) quickly (within a few weeks) settle on this surface.

Some checks are abandoned untreated. In this case, significant amount of organic and mineral sediment is preserved in them. It is composed of pronounced thin layers deposited by water. When the check is abandoned, this material becomes the soil-forming rock. Our data show that the thickness of sediments formed during the period of operation of the checks from 1973 to 2001 varies within 190–320 cm at the Peny factory and within 80–120 cm at the L’gov factory. Differences in the degree of layering, contents of particular fractions, and thickness of the layers in soil profiles are related to different hydrological regimes of the checks, duration of their use, and a number of other more specific factors. The predomination of coarse silt fractions in the composition of sediments and a very low content of coarser particles is their common feature.

When dried, sediments are mechanically removed, and the lower part of the abraded soil profile or the initial soil-forming rock is exposed to the surface. New post-technogenic soils are formed on this material transformed under the impact of mineralized wastewater after the stop of the use of checks and during vegetation growth.

The composition of industrial wastewater discharged to the infiltration fields of the L’gov sugar factory. L’gov sugar factory processes about 2300 tons of sugar beet per day [22]. According to data of 2009 [34], the total discharge of untreated wastewater formed during the sugar beet processing season (of the mean duration of 110 days, September–December) was up to 755 000 tons. The improvement of the purification technology at the plant in recent years has caused a significant decrease in the volume of discharged wastewater to 483 110 tons [49].

The updated information on the component composition of wastewater from the L’gov sugar factory (sampling of 2021) enables us to compare them with those obtained earlier [20, 56] and to determine specific impact of wastewater on the environment and soils. It consists in the input of a wide range of geochemically active substances, of mineral suspensions, in particular; organic matter; ammonium ions; calcium, iron, and manganese compounds; and trace elements (Table 3).

Table 3.   Composition of wastewater of the L’gov sugar factory (sampling of 2021)
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In addition, a particular amount of technological aids used in sugar production (antiscalants, surfactants, defoamers, etc.), pesticides, and pathogenic microorganisms are supplied to IFs with wastewater [6, 8, 21, 38].

Filtration (sugar defecate) and conveyor-washing sediments are important factors of the formation and chemical transformation of soils on IFs along with wastewater. The technogenic effect of defecate is determined by the high content of carbonates (40–80%), organic matter (10–30%; for comparison, 21% in manure), nitrogen (0.2–0.7%), phosphorus (P2O5) (0.5–0.7%), potassium (K2O) (0.2–0.7%), iron (to 0.2%), copper (0.0007–0.0008%), manganese (0.005–0.75%), etc., as well as by the presence of heavy metals (Zn, Ni, Pb, and Cd), the content of which may exceed the regional background levels [16, 25, 34].

The material of the conveyor-washing sludge deposited from wastewater is a source of fine earth (about 93%) rich in organic matter, which adheres to sugar beet root crops and is removed from agrogray soils and agrochernozems during harvesting [8, 31, 42]. In addition, the sediments contain fragments of sugar beet roots, tops, pulp, peel, as well as sugars, acid beet saponin, sulfates, chlorides, pathogenic microorganisms, and other admixtures [8, 31].

The fine earth of the sediment is dominated by fractions of 0.25–0.005 mm (36.9% of coarse silt, 23.4% of medium silt, and 22.6% of fine sand). Experiments at a number of sugar factories have shown that the deposition rate of particles of different sizes on the bottom of the checks varies from 0.01 to 3 mm/s [39]. A particular amount of coarse suspended matter (>0.25 mm) is lost with clarified water due to an improper hydrodynamic regime in operating settling reservoirs. This is related to the peculiarities of their design, resulting in the appearance of zones with high water flow rates.

Thus, the general technogenic impact on the environment and soils in the areas of disposal of waste of the sugar industry is related to: (1) withdrawal of land for the organization of IFs; (2) discharge of wastewater of multicomponent composition mixed with defecate and conveyor-washing sediment enriched with organic compounds, carbonates, and nutrients; (3) the input of soluble salts, heavy metals (the content of which still requires investigation), phosphates, technological aids, saponin, and microorganisms contained in untreated wastewater; they are often toxic and dangerous to the natural environment and soils.

The abundance and diversity of organic and mineral substances not typical for regional natural conditions, which enter treatment facilities, precipitate in them, and are involved in soil formation and geochemical flows, may be assigned to excess resources [11, 12] in comparison with soil-forming resources of chernozems.

RESULTS AND DISCUSSION

Six groups of soils were identified in IFs according to specific factors (geomorphic position, duration and regime of wastewater inflow, type of substrate, composition of vegetation, duration of the use of checks, their modern status, and the use of checks after abandonment) and the features of soil formation.

Soils of Earth Walls of Filtration Fields

I-1. An invasive extremely aggressive species—ash-leaved maple (Acer negundo)—is widely spread on the walls composed of a mixture of the material of background natural chernozems and loess-like loam extracted from checks during their construction. Soils under its thickets with dead ground cover are described by the most typical pit LG-02-20. According to the soil profile formula AU (1–2 cm)–C (1–5 cm), they are assigned to dark humus typical soils, corresponding to the division of organic-accumulative soils (Fig. 2f). Taking into account the high pH and CaCO3 content (Fig. 3), as well as total exchangeable bases (from 45 to 48 meq /100 g soil) in similar soils of L’gov IFs [34], we assign these soils to Eutric Cambisols (Organotransportic) according to the WRB [52].

Fig. 3.
figure 3

Some physicochemical and chemical properties of soils at the bottoms (a) and on the walls (b) of checks of infiltration fields of sugar factories. Pit LG-10-20—mucky-humus quasi-gley artistratified soil (group II-1), pit PN-03-21—dark-humus soil on artifimostrate (group II-2), pit LG-02-19—mucky–dark-humus quasi-gley soil (group II-3), pit LG-01-20—migrational–mycellary quasi-gley chernozem (group II-4), pit LG-08-20—technogenic humus pelozem on artiindustrate (group I-2), and pits LG-02-20 and LG-03-20—dark-humus typical soil on organolithostrate (group I-1).

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Dark-humus typical soils (pit LG-02-20 (51°37.348′ N, 35°15.847′ E), pit LG-03-20 (51°36.818′ N, 35°15.389′ E), and pit LG-06-20 (51°36.902′ N, 35°14.913′ E) include clearly defined dark gray (10YR 3/2) or brownish-dark gray (10YR 2/2, 10YR 2/2–2/3) dark humus horizons of about 30 cm in thickness or more, with distinct angular blocky to granular coprogenic structure. They are characterized by the alkaline reaction (pH 8.1–8.3), the presence of carbonates (0.6–1.4% of CaCO3) and organic carbon (3.1–4.0%), and by the medium C-to-N ratio (12–14) (Fig. 3b).

Bulk density (0.96–1.05 g/cm3) and penetration resistance (10–20 mm) of the newly formed dark humus horizon are lower as compared to the underlying material (1.22–1.26 g/cm3, 24 mm or more). This is favored by intensive phyto- and zooturbation due to the abundance of horizontal strongly branched roots of ash-leaved maple and the activity of soil macrofauna, primarily of saprophages: earthworms (Lumbricidae), and annelid worms (Enchytraeidae). The change in the content of carbonates (CaCO3) along the profile depends on their initial content in the displaced material. Soils on walls of this type are in general formed under the impact of modern soil-forming processes. Within about 70 years after the creation of walls, a well-shaped humus horizon is formed in the soils, biogenic structuring is developed, and the profile is differentiated by density and penetration resistance. However, properties of the initial material of the walls may be preserved below the humus horizon.

I-2. Specific soils are formed on the walls covered by solid waste from sugar factories—pale gray (10YR 7/2) clay defecate enriched with organic matter—under tall grass and reed communities with the participation of ash-leaved maple (dominants include Atriplex sagittata, Urtica dioica, Artemisia vulgaris, Phragmites australis, and Acer negundo). These soils were described in pit LG-08-20 (51°37.500′ N, 35°15.373′ E). Defecate may be assigned to technogenic surface formations (TSF)—artiindustrates of the group of artifabricates according to the new Russian soil classification system [23, 30]. Their profile consists of the protohumus horizon W and the underlying technogenic calcareous sediment (W–TCHca(1-3)). They are classified as technogenic humus pelozems on artiindustrate of the order of incompletely developed soils (Fig. 2e). Note that small symbol ca in this case denotes technogenic (not lithogenic) carbonates brought with wastewater. According to the WRB classification [52], these are undoubtedly Technosols; their composition and properties are partly reflected in a series of qualifiers: Spolic Technosols (Alcalic, Calcaric, Transportic).

Technogenic pelozems (pit LG-08-20) consist of a 5- to 10-cm-thick heterogeneous surface horizon with the yellowish gray (10YR 5/2) (owing to the presence of carbonates) background color and dark gray (10YR 6/2) and brown gray mottles (Fig. 4g), loose subangular blocky structure, and abundant fine roots. The features of pedogenesis in the main mass of defecate are poorly pronounced in the form of staining with organic matter and bioturbation. Specific properties include a high content of carbonates (52.7–65.5%, defecate carbonates) and organic carbon (7.8–13.6% of Corg) due to abundant dispersed organic residues, as well as a very high organic carbon to total nitrogen ratio (C/N = 27–40) (Fig. 3b). The pattern of these properties in the vertical soil profile clearly indicates the presence of buried organic remains at a depth of 35–40 cm. In general, the properties reflect strong preservation of technogenic material, which is slightly transformed only in the surface layer.

Fig. 4.
figure 4

Mesomorphology of soils of infiltration fields: (a) loose micrite carbonates and organic matter in the AH horizon (0–5 cm), pit LG-10-20, ×32; (b) vivianite in the Q1 horizon (5–30 cm), pit LG-10-20, ×80; (c) humified wormhole material in the BCA2mc horizon (50–65(70) cm), pit LG-01-20, ×25; (d) iron accumulation along root channels in the AB2mc horizon (22(30)–35 cm), pit LG-01-20, ×32, (e) carbonate pseudomycelium (veins along root channels) in the BCA4mc,q horizon (from 80- to 105-cm-thick), pit LG-01-20, ×12.5; (f) carbonates in the form of scattered sparite crystals in the BCA3mc,q (65(70)–80 cm), pit LG-01-20 section, ×25; (g) defecate: contact of whitish calcareous material (1) with brown material (2) with black spots and micro layers (3) in the TCH3 horizon (50–70 cm) of pit LG-08-20 on the defecate wall, ×6; (h) alternation of light-colored (1) and dark-colored humus microlayers (2) in defecate sediments in the ТСН3ca,rr horizon (40–65 cm), pit PN-03-21.

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Soils at the Bottoms of Checks of Infiltration Fields

II-1. Two soil profiles were described on annually flooded for 2–3 months and then drying bottoms of the operating checks of the L’gov sugar factory. The pits were dug at the boundary between the watered and drying surfaces completely covered by hydrophilic plants, mainly duckweed (Lemna minor); mesophilic herbs were present along the sides of the check. Soil pit LG-10-20 (51°37.604′ N, 35°15.014′ E) with the AHca,dc–ТСНca,rr–Q1–Q2mc horizonation characterized a mucky–humus quasi-gley artistratified soil (Fig. 2a). According to the WRB [52], it corresponds to Calcaric Gleysol (Alcalic, Clayic); and technogenic stratification could be reflected by the missing Technofluvic qualifier. Soil pit LG-06-22 (51°37.646′ N; 35°14.646′ E) with the Нca–TCH–Q1ca,rr–Q2mc characterizes a mucky quasi gley artistratified soil.

Soils of the hydromorphic series are formed on sewage sediments in the operating checks. Despite the fact that the checks have been in use for about 70 years, the soils represent short-term yet clearly pronounced stages of pedogenesis during each period of drainage (aeration), the duration of which ranges from several weeks to several months.

The soils at check bottoms are characterized by dark brown (2.5Y3/2) mucky slightly peaty or brownish dark gray mucky–dark-humus (7.5YR 2/2) horizons with abundant moderately decomposed plant residues and poorly shaped subangular blocky organomineral microaggregates (Figs. 4a, 5a, 5b). Carbonate pedofeatures in the form of loose micritic concentrations and impregnations and calcified plant residues are detected in the AH horizon (Figs. 4a, 5b). Organic horizons 5–10-cm-thick gradually give way to the technogenic thin-stratified layer (TCH) slightly transformed by soil processes and representing an alternation of carbonate and organic micro-layers (Fig. 5c). Below, quasi-gley horizons (Qmc) are formed. Soils contain a large content of carbonates (Fig. 3a) with a maximum in the upper horizons (18.0–20.0%); in the lower layers, the content of carbonates decreases to 6.4–7.6%. In the lower part of the profile, carbonates are represented by micritic impregnation and sparite veins along root channels (Fig. 5d).

Fig. 5.
figure 5

Micromorphology-of soils of infiltration fields: (a) large moderately decomposed plant residues (1) and organomineral aggregates (2) in the AH horizon (0–5 cm) in pit LG-10-20, ×25, PPL; (b) calcified plant residues, where carbonates are represented by large sparite crystals (1), carbonate micrite impregnation of the main mass (2), and organic matter in the form of moderately decomposed plant residues (3) in the AH horizon (0–5 cm) in pit LG-10-20, ×25, XPL; (c) carbonate sparite (1), organic (2), and carbonate micrite (3) micro-layers in defecate, ТСНca,rr horizon (5–25 cm) in pit LG-10-20, ×50, XPL; (d) carbonate sparite veins along root channels in the Q2mc horizon (30–50 cm) in pit LG-10-20, ×25, XPL; (e) phosphate coatings in the BCAdc horizon (30–40 cm) in pit LG-02-19, ×100, PPL; (f) iron accumulation in the main mass of the horizon around strongly decomposed plant residues (1), carbonate micrite pedofeatures along root channels (2), carbonate micrite-microsparite spots (3) in the Q horizon (40–70 cm) in pit LG-02-19, ×40, XPL; (g) carbonate micrite micronodules/small spots (1) and carbonate impregnation in biogenic aggregates (coprolites) (2) in the AH horizon (0–10 cm) in pit LG-02-19, ×40, XPL; (h) carbonate sparite pedofeatures along root channels (1) and iron accumulation in the main mass around plant residues in the Q horizon (40–70 cm) in pit LG-02-19, ×40, XPL; (i) rounded biogenic aggregates (coprolites) in the AU horizon (0–5(8) cm) in pit LG-01-20, ×25, PPL; and (j) carbonate sparite pedofeatures along root channels in the BCA1mc horizon (35–50 cm) in pit LG-01-20, ×25, XPL.

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Hydrogenic metamorphism is manifested from a depth of 25 cm in the form of gray bluish colors (2.5YR 6/4) with rusty iron mottles, iron concentrations along root channels and pores, and with specific phosphate minerals. At a depth of 25 cm, there are vivianite (Fе3[PO4]2·8H2O) Fе3[PO4]2·8H2O) segregations up to 150 µm in size of grayish-bluish color of spherical, flat, or irregular shape, sometimes with a pronounced luster (Fig. 4b). Phosphate accumulation in quasi-gley horizons is confirmed by analytical methods. The total phosphorus content reaches 0.31–0.36%, which enables the assignment of the studied soils to the subtype of chemically contaminated soils, the genus of soils with excessive accumulation of phosphates [23, 30, 33].

The soil reaction is alkaline throughout the profile (pH 7.8–8.5). Alkalinity is mainly related to regular input of carbonates with wastewater and with the abundance of carbonates and carbonate pedofeatures in the initial material on the bottoms of checks. The organic carbon content in soils is high (Fig. 3a): from 7.21% in the AH mucky–humus horizon to 1.13% in the lower Q quasi-gley horizon. The soils are strongly enriched with nitrogen in the surface horizons (C/N = 12); in the lower horizons, the C/N ratio increases to 21–25 attesting to the slow organic matter mineralization.

The analysis of water extracts from this soil indicates that the content of almost all water-soluble forms of elements in the soils of the used check does not exceed the values typical for background soils [14, 37]. The exception is represented by the noticeable accumulation of sulfate ions \({\text{SO}}_{4}^{{2 - }}\) in the organic horizon (0–5 cm), where its content reaches 440 mg/L. In deeper layers, the content of sulfate ions does not exceed 50–60 mg/L, which is typical for background soils and for other soils at the bottoms of abandoned checks. Despite the content of lime suspensions in wastewater and the presence of defecate, the concentration of Ca2+ does not exceed its mean concentration in water extracts from the background forest-steppe chernozems (155–390 mg/L) [14, 37]. Thus, if even excessive amounts of soluble salts enter the soil, they are easily removed from it with the outflowing wastewater and atmospheric precipitation.

Periodic input of fine material of conveyor-washing sediment to the surface of checks with wastewater is reflected in soil morphology: there is a particular differentiation of soil texture from clayey–coarse silt loam in the upper part to clay loam or clay in the lower part of the profile (Table 4). The amount of sand fractions (1–0.25 and 0.25–0.05 mm) is minimal. It has been already mentioned that they are removed due to the specific hydrodynamic regime in the settling tanks (at high water speeds).

Table 4.   Particle-size distribution in soils on operating and abandoned checks of infiltration fields
Full size table

In addition to their specific morphology and chemical properties, mucky–humus quasi-gley artistratified soils are also characterized by specific functioning with high rates of carbon dioxide emission in summer (0.41 g C (CO2)/(m2 × h) that exceed several times the emission from background chernozems [20]. The analysis of CO2 emission from checks of IFs shows that the more frequent flooding, the greater the emission. In our opinion, this is mainly related to the inflow of wastewater rich in organic substances. In this case, the emission is almost exclusively caused by the microbiota activity. Microbiological processes of organic matter destruction are very intensive mainly due to bacteria (5.6 × 106 CFU/g), while the numbers of actinomycetes and especially micromycetes (mold fungi) are insignificant (to 100 CFU/g) [56].

II-2. Soils on thin-stratified mineral and organic waste from sugar production have been studied in dry bottoms of abandoned checks of IFs of the Peny sugar factory, where sewage sludge remained. The checks have not been flooded for 20 years by the time of the description. Soil pit PN-03-2021 (51°38.372′ N; 35°30.399′ E) was described under dense association of nettle (Urtica dioica). It had the following horizonation: AUdc–AU–ТСНca,rr–ТСН2-7 ca,rr,(rh),(q) (Fig. 2b). The soil was classified by us as a dark-humus artistratified soil on the artifimostrate [23, 30]. According to the WRB [52], the soil may be assigned to Spolic Technosols (Alkalic, Calcaric) with some assumption, since stratification as a qualifier is absent in this reference soil group.

These soils could be considered within the synlithogenic trunk of soil formation as dark humus stratozems with the RU horizon [23]. However, according to this name, which formally reflects soil profile morphology, the soil is assigned to natural formations, and its technogenic specificity is lost. The properties of the RU stratified dark-humus horizon do not correspond to those of the studied objects, because the basis of stratified horizons is formed not by humus material, but by mineral high-carbonate sewage sludge with very thin layers of dispersed organic matter. They may reflect microstages of humus formation and are covered by abundant mineral material annually supplied with wastewater, which comprises the main mass of the strata in the horizon (Fig. 4h). This structure is more accurately described by the TCH symbol of the technogenic horizon with qualifiers ca and rr, reflecting the presence of carbonates and technogenic stratification. We suggest that the TCH symbol can be used for designation of strata-horizons of similar soils of technogenic landscapes: it distinguishes them from soils of natural synlithogenic soil formation of the similar structure with the stratified RU horizon (dark-humus stratozems). When the check dries up, the technogenic layer is transformed to some degree by pedogenetic processes. The term artistratified indicates the technogenic origin of stratification and enables more adequate explanation of the genesis and properties of such soils.

The profile consists of the AU dark-humus dark gray horizon with a brownish tinge (10YR 2/3), 10 to 15 cm in thickness, gradually replaced by a stratified layer with alternating organic dark gray tinted brown (10YR 2/3) and light pale mainly calcareous 1–2-cm-thick interlayers (10YR 6/2-5/2) deposited from wastewater and other effluents during the operation of the checks (Fig. 4h).

The reaction of the soils is alkaline (pH 8.2–8.5), and the content of carbonates is high throughout the profile (22–33%). Dark humus horizons of soils (the carbon content is 2.25–2.42%) are characterized by the low C-to-N ratio, which is related to technogenic enrichment with organic matter. The carbon content decreases with depth, remaining quite high (1.86%) at a depth of 50–65 cm (Fig. 3a).

The soil texture is expectedly heterogeneous due to technogenic stratification. Only the surface horizons (to a depth of 30 cm) are characterized by the same silt (mainly, coarse silt) loamy texture. An increase in the content of physical clay (53.8%) at a depth of 30–40 cm is caused by the organic material of the conveyor-washing sediment. The maximum penetration resistance and hardness at this depth (28–30 mm) confirms the presence of a compacted area, representing a local aquiclude, above which small diffuse mottles of iron hydroxide concentrations are formed. The second aquiclude is seen in the lower part of the profile from a depth of 65 cm. This is a quasi-gley layer (10YR 4/2–10YR 6/2) with poor filtration and aeration, intensively effervescing with HCl, and with single small diffuse iron concentrations of 5–7 mm in size.

Evidences of synlithogenic soil formation in soils of abandoned untreated checks become less pronounced within a 20-year period, which is especially well seen in the upper parts of the profile, where the initial layers are transformed into relatively homogeneous soil horizons of postlithogenic soils. Postlithogenic soil formation in dark-humus artistratified soil consists of the input and transformation of plant residues, humus formation, mesofauna activity, coprolite formation (coprolites are seen to a depth of 40–65 cm), and the formation of biogenic subangular blocky to granular structure. The transformation of the material in the layers of sewage sludge by pedogenic processes becomes weaker from a depth of 30–40 cm. There are data, which testify to low probability of a complete convergence of the properties of dark-humus artistratified soils with the properties of background natural soils. There are cases, when the industrial trace related to residual defecate stratification still persists in zooturbated soils of the infiltration fields of sugar factories abandoned more than 100 years ago in Ukraine [40].

According to published data, the availability of nutrients (NPK) in soils of IFs of sugar factories is very high. Their content comprises (mg/kg) 229.0 for available phosphorus (P2O5), 404.0–648.4 for exchangeable potassium (K2O), and 148.5–183.0 for easily hydrolyzable nitrogen (NO3) [37, 38]. For comparison, the content of these nutrients in the surrounding agrochernozems is significantly lower: 155.1, 91.8, and 43.1 mg/kg, respectively.

According to our data [20], favorable agrochemical properties are accompanied by the increased content of Cd (0.17–0.33 mg/kg; the clarke is 0.09 mg/kg; and the background content is 0.12 mg/kg) and Zn (47– 62 mg/kg; the clarke is 75 mg/kg, and the background content is 44 mg/kg) as compared to chernozemic loamy soils. This may limit their use as potential agricultural lands. However, areas near the roads within the analyzed checks are regularly used by local residents for vegetable gardens. Some checks of the Peny sugar factory were used after its closure for sowing herb mixtures for forage production. A detailed examination of both the content of heavy metals and the microbiological state of these soils is necessary for their reclamation and potential involvement in agriculture.

II-3. The checks of the L’gov sugar factory cleaned of sewage sludge and abandoned about 30 years ago with the temporary perched water table were covered by hygrophilous vegetation—dense thickets of common reed (Phragmitetum australis association)—during our study. Carbonate loess-like loam and, possibly, the remains of abraded initial chernozems, which were exposed during the construction of the checks, and then buried under sewage sediments for over 40 years have been subjected to pedogenesis after the partial or complete removal of accumulated sewage sludge. The modern soil is characterized by both technogenically inherited (high content of phosphates, carbonates, and a number of heavy metals) and lithogenically inherited (particle-size composition) properties and those formed during the past 30‑year period. The latter include organic matter accumulation; biogenic processing; carbonate, ferruginous, and phosphate pedofeatures, hydrogenic metamorphosis; and differentiation into horizons.

Soil pit LG-02-19 is characterized by the profile formula АHdc–AU–AB–BCAdc–Qmc. This soil is assigned to mucky–dark-humus quasi-gley bioturbated soils (Fig. 2c). According to the WRB [52], they may be classified as Gleyic Cambisols (Alcalic, Loamic, Protocalcic).

They are diagnosed by four horizons: the organic O horizon composed of reed debris with a thickness of up to 25 cm; the mucky–humus AH horizon of dark gray (10YR 3/1) to black (10YR 1.7/1) color; the dark humus (AU, 10YR 3/1) horizon, and the underlying nonuniformly colored (with brownish dark gray (10YR 3/2) mottles against dull yellowish brown (10YR 5/4)) background color quasi-gley horizon (Q).

The Corg content is maximal in the surface mucky–humus horizon due to abundant organic residues (4.18%), drops in the dark-humus horizon to 1.97%, and then gradually decreases with depth to 0.59% at the lower boundary of the quasi-gley horizon (Fig. 3a). The soil reaction is strongly alkaline throughout the profile (pH 8.6–9.1).

The AH and AU horizons with a total thickness of about 25 cm consist of the humified, well-structured (granular–subangular blocky) material with amorphous (mucky) substance in the surface part; the humus horizons contain abundant coprolites (Fig. 5g) and channels left by soil fauna and roots. The amount of carbonates does not exceed 2.9% (Fig. 3a); morphologically, these are calcified plant residues (with microsparite and sparite crystals) and mottles of calcite concentrations (or microsegregations) (Fig. 5g).

The quasi-gley horizon is characterized by the angular blocky structure and contains many wormholes and coprolites and large passages of reed roots, which penetrate to a depth of 2–3 m or more. Pedofeatures appear due to redistribution of iron oxides in the form of micronodules and iron accumulations along the pores with strongly decomposed plant residues indicating the possibility of short-term oxidative conditions (Figs. 5f, 5h). Iron, passing into dithionite–citrate–bicarbonate extract (Fed), is slightly accumulated in the quasi-gley horizon (0.67%) as compared with the upper layers (0.40–0.45%). The horizon contains stable forms of pedogenic carbonates (Figs. 5f, 5h): carbonate pseudomycelium (veins/tubules/coatings along root channels), calcified plant residues, and scattered sparite crystals. The number of carbonate mottles /microsegregations is noticeably greater than in the overlying zones of the profile (AB and BCAdc horizons).

The sources of carbonates during their further recrystallization and formation of pedogenic carbonate neoformations may be represented by both initial carbonate rocks—loess-like loams—and by wastewater. Carbonates in the lower part of the profile are mainly illuviated from the overlying strata during the movement of wastewater along the profile, and pedogenic carbonate features appear.

Phosphate pedofeatures (translucent, orange, often with an internal radiant texture) are seen at the microlevel in the quasi-gley horizon at a depth of 30–40 cm. There are separate amorphous clusters, thick phosphate coatings along pores (Fig. 5e), as well as separate formations (resembling lemon slices); the total phosphorus content is high (0.21–0.24%). This enables the assignment of mucky–dark-humus quasi-gley soils together with the soils of operating checks (pit LG-10-20) to the group of soils with excessive content of phosphates [33]. They are also characterized by an increased Cd content in the upper horizons (0.17 mg/kg) as compared to clarke and the background for chernozemic soils; Cd is obviously contained in substances used in sugar production as component of wastewater and defecate [34]. The contents of Zn, Ni, Cu, and Pb in the soil horizons do not differ from those in the background chernozems.

The soils are characterized by silt loamy texture without evidences of pedogenic differentiation of the clay fraction. Fractions of coarse silt and clay predominate in the fine earth. The amount of sand fractions (1–0.25 and 0.25–0.05 mm) is minimal, which is typical for all the studied soils at the bottoms of both operating and abandoned checks of IFs.

The CO2 emission from abandoned checks of IFs under ordinary reed is 0.17 g C (CO2)/(m2 × h) in the summer period, which is 2.5 times lower than that from the surface of used watered checks [20].

II-4. The checks of IFs of the L’gov sugar factory abandoned 40 years ago and cleaned of sewage sludge are characterized by pit LG-01-20. Similar to the described above check, the soils are formed on the exposed residual material of the abraded initial soils. The surface of the check bottom is covered by dense thickets of ash-leaved with complete canopy closure (the Aceretum negundi association). The modern soil has both inherited features and the features formed over the past 40-year period. The most pronounced of them include the organic matter accumulation, biogenic structuring, phyto- and zooturbation, the presence of iron and phosphate pedofeatures, and differentiation into horizons. The formula of the soil profile is AU1-2–AUB1-2 (mc)–BCA1-4mc(q) (Fig. 2d).

According to the WRB [52], the soil may be classified as Haplic Cambisol (Alcalic, Protocalcic). It is more difficult to give an adequate name to this soil using the modern Russian classification. According to the profile morphology and taking into account the water regime of the check, which is periodically filled with rain and snowmelt waters, it should be most obviously assigned to meadow-chernozemic soils [24], which with some approximation correspond to quasi-gley zooturbated chernozems [23, 30].

The dark humus horizon of the soil is mainly dark gray (10YR 2/2-2/3), loose (the density is 0.91–0.99 g/cm3, and penetration resistance is 15–20 mm), and with subangular blocky to granular structure (Fig. 5i). The total thickness ranges from 8 to 12 cm in dark-humus horizons to 22–35 cm in the AUB transitional horizons. They are underlain by grayish light brown (10YR 5/3–6/3) well-structured loamy horizons with numerous traces of bioturbation. Below, there are light brown to pale yellow (10 YR 5/3–10YR 5/4) carbonate accumulative horizons with small iron nodules (BCAmc,q). Evidences of iron accumulation in the profile already appear from a depth of 22 cm in the form of rounded rusty spots and iron coatings along root channels (Fig. 4d).

Evidences of biogenic transformation of material in the soil profile are numerous and diverse and are seen to the lower horizons. These are biogenic pores of different sizes and shapes: channels of mole rats, mesofauna (saprophages), and roots with transported soil mass (Fig. 4c); coprolites of various sizes, morphology, and preservation (Fig. 5i); and plant residues of various decomposition degrees. The impact of strongly branched root systems of ash-leaved maple with lateral roots is especially pronounced.

The organic carbon content in the upper horizons of soils is moderate (Corg = 2.7%) and gradually decreases down the profile to 1.54% at a depth of 70–80 cm (Fig. 3a). The organic carbon-to-nitrogen ratio is similar in all soil horizons, and they are enriched with nitrogen (C : N = 9–10). For comparison, the C‑to-N ratio in plowed and postagrogenic chernozems of Kursk oblast is 10–18 in the humus horizons and varies from 33 to 63 in carbonate-accumulative horizons [53]. The soil reaction is strongly alkaline (pH 8.6–9.1) throughout the soil profile (Fig. 3a). These soils differ in pH from the background chernozem, in which acid-base conditions vary along the profile from slightly acid to alkaline [46, 54].

The content of carbonates is high (9.9–11.0%) in all horizons of the profile (Fig. 3a), while background soils are carbonate-free in humus horizons to a depth of 80 cm. Meso- and micromorphological studies have shown an abundance of various forms of carbonates throughout the profile; pseudomycelial forms (veins, tubules, and coatings along root channels) are detected from a depth of 22 cm (Figs. 4e, 5j). The carbonate-accumulative horizon contains clusters (carbonate spots/microsegregations) and scattered crystals of sparite in addition to impregnations and pseudomycelium (Fig. 4f). The BCA horizons in the studied and natural soils [46, 54] contain similar forms of pedogenic carbonates.

The texture of loess-like loam is preserved in the soils: they are mainly silty clay loamy soils with a predominance of coarse silt fraction (Table 4) and without differentiation of the clay fraction along the profile.

The rate of CO2 emission from unused checks of IFs under dense thickets of ash-leaved maple does not significantly differ from that in the chernozems and is about 0.08 g C–CO2/(m2 × h) in summer [19].

The high soil formation rate and the formation of soils close to chernozems in a short period (40 years) after the exposure of substrates buried under sewage sediment may be explained by previous input of extremely rich organic and mineral resources, favorable water regime without moisture stagnation, productive plant covers formed in abandoned checks, and high biota activity. However, a different more correct classification may be required, taking into account the humification rate and the nitrogen enrichment of the organic matter.

CONCLUSIONS

Specific landscapes of treatment facilities—infiltration fields—are formed in the areas of disposal of sugar industry waste. According to our observations, a particular combination of conditions, as compared to the surrounding background, is created in the accumulative positions of artificial mesodepressions (checks) surrounded by earth walls:

(1) Thicker and more long-term snow cover and, consequently, higher soil temperature in winter (we do not give weather data here due to a short series of terrain survey);

(2) Periodic watering of the used checks with additional input of biogenic and other substances used in beet processing and sugar refining;

(3) Widespread hydrophilic and hygrophilic plant communities predominated by mesophytes and xeromesophytes, which are not typical for background forest-steppe landscapes of the central chernozemic region;

(4) Soil-forming substrates in IFs are represented by multicomponent waste of sugar industry and carbonate loess-like loams transformed by sewage and/or the lower horizons of chernozems.

Their properties, composition, and genesis differ from all known soil-forming rocks, and they are new objects for studying soil formation with a known zero moment. All this makes IFs specific objects of a technogenic landscape, interesting for studying soil formation.

A wide range of technogenic and post-technogenic soils not typical for natural background is formed in these landscapes. They comprise a soil cover, differing from the original one, the complexity and contrast of which is related to variegated geomorphic conditions, soil-forming substrates, cycles of watering–drying of checks of IFs, specific features of the plant cover, and the use of checks after abandonment for arable farming and vegetable gardens.

The soils are allocated to different elements of checks of IFs and, consequently, differ in their morphological and analytical properties.

The studied soils of the postlithogenic trunk of soil formation are assigned to four orders:

(1) Poorly formed soils on walls covered by defecate (technogenic pelozems on the artiindustrates);

2) Organic-accumulative soils on walls between checks on natural material (dark humus typical soils on organolithostrates);

(3) Quasi-gley soils in the bottoms of the used checks (mucky and mucky–humus quasi-gley soils) and abandoned checks without the removal of sediments (dark-humus technogenic artistratified soils), which combine properties of postlithogenic and synlithogenic soils; this order also includes (mucky)–dark-humus quasi-gley soils with pronounced bioturbation formed under high humidity in the bottoms of abandoned checks cleaned of sediments;

(4) Accumulative-humus soils in abandoned checks cleaned of sediments (quasi-gley chernozems) under the cover of tree species predominated by ash-leaved maple under conditions of periodic moistening regime.

The input of solid-phase and/or chemogenic material, hydrogenic metamorphism in an alkaline medium, and mineralization and migration of various substances, including soluble salts (sulfates) are more active in soils of operating checks, while metamorphism of organic and mineral matter and structuring and turbation related to the activity of biota and roots dominate in soils of abandoned checks.

With respect to the sum of the features or their particular combinations, direct natural analogues of the formed soil bodies in the checks of IFs are absent in the central chernozemic region. Alkaline and strongly alkaline soils enriched with organic matter, carbonates, phosphates, nutrients, and a number of heavy metals on waste of the sugar industry are an example of extreme soils forming under an excess of resources and the influence of sugar industry [11, 12]. In addition to the specific morphological and chemical properties, soils of the bottoms of IFs are characterized by specific functioning related to increased rates of the emission of greenhouse gases and microbiota activity [20].

The results obtained show that a variety of extreme soils formed under the impact of strongly concentrated wastewater from enterprises of different branches of the food industry (techno-hydro-extreme) and characterized by a particular behavior may be distinguished.

From the point of view of classification of land ecosystems, checks of IFs may be considered anthropogenic ecosystems of accumulative type with additional material and energy input with sewage, defecate, and conveyor-washing sediment. Remote analogues of such ecosystems in nature are regularly covered by water floodplain meadows, alas depressions on permafrost, and marches of accumulative seashores [13, 15, 28, 45].