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Article

Comparative Assessment of the Resistance to Lead (Pb) Pollution of Forest, Forest-Steppe, Steppe, and Mountain-Meadow Soils of the Central Ciscaucasia and the Caucasus Regions

by
D. I. Moshchenko
1,*,
Sergey I. Kolesnikov
1,
A. A. Kuzina
1,
Kamil S. Kazeev
1,
Tatiana M. Minkina
1,
A. A. Mezhenkov
1,
Y. A. Litvinov
1,
Sudhir S. Shende
1,*,
Saglara S. Mandzhieva
1,
Svetlana N. Sushkova
1 and
Valery P. Kalinitchenko
2
1
Academy of Biology and Biotechnology Named after D. I. Ivanovsky, Southern Federal University, 344090 Rostov-on-Don, Russia
2
Institute of Fertility of Soils of South Russia, 344000 Rostov-on-Don, Russia
*
Authors to whom correspondence should be addressed.
Forests 2022, 13(10), 1528; https://doi.org/10.3390/f13101528
Submission received: 11 August 2022 / Revised: 8 September 2022 / Accepted: 15 September 2022 / Published: 20 September 2022
(This article belongs to the Special Issue Pollution, Heavy Metal, and Emerging Threats in Forest Soil)
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Abstract

:
Lead (Pb) is one of the most hazardous heavy-metal pollutants in the environment. However, the resistance of different soils and ecosystems to Pb pollution varies greatly. In the present study, the comparative assessment of the resistance to Pb contamination in the forest, forest-steppe, steppe, and mountain-meadow soils of the Central Ciscaucasia and the Caucasus regions was conducted. There were 10 types and subtypes of objects from the forest, forest-steppe, steppe, and mountain-meadow soils which were selected for this study. The laboratory modeling of the effect of chemical soil contamination with lead (II) oxide (PbO) at different concentrations, 100, 1000, and 10,000 mg/kg, were introduced into the soil to check the microbiological, biochemical, and phytotoxic properties of the soil after 30 days of incubation. Soil resistance to Pb stress was assessed by the degree of the decrease in the most sensitive and informative biological indicators of the soil condition. It has been found that the forest-steppe and steppe soils showed a greater resistance than that of the forest and mountain-meadow soils. The regional maximum permissible concentration (rMPC) of Pb was developed for the first time, according to the degree of violation of the ecosystem functions of the soils. The forecast maps were developed for the deterioration of the soil condition during the Pb contamination at variable concentrations in the Central Ciscaucasia and the Caucasus regions.

1. Introduction

Soil is the central link in the cycle of substances in terrestrial ecosystems, which determines the fixation of heavy metals in it and, accordingly, the resistance of the entire ecosystem to the pollution [1,2,3,4]. Lead (Pb) is one of the priority pollutants and recognized as a highly hazardous chemical element in the new European Commission’s Registration, Evaluation, Authorization, and Restriction of Chemicals (EC REACH) regulations [5]. Sources of Pb pollution in the environment, including soils, are road and rail transport, coal mining, non-ferrous and ferrous metallurgy enterprises, and lead-containing substances used in everyday life, such as lead-based paints, lead-glazed ceramics, lead-based solder, and herbicides containing a significant amount of lead (Pb3(AsO4)2) [6,7,8].
The increased level of Pb in the soil environment has an adverse effect on soil microbial diversity [9,10,11,12], plants [13,14,15,16,17,18], and on human health also [19,20,21]. Lead compounds are carcinogenic and genotoxic, causing the mutations and disturbances in the tertiary structure and functions of enzymes that help in the DNA synthesis and repair mechanisms [11]. The long-term use of tetraethyl lead, which is an additive in automotive fuels, has significantly contaminated the areas beside highways with Pb [22,23,24,25]. The use of Pb as an additive in gasoline and house paint has contributed to the accumulation of anthropogenic Pb in soils, which has been significantly reduced since the ban came into force between the 1970s and 1990s [26]. However, the contribution of these Pb sources persists and continues to impact public health [27,28]. The most recent studies have shown that even decades later, Pb stored in soils is a constant source of environmental pollution because of the remobilization and deposition of contaminated dust [27,29,30]. The soils of the Central Ciscaucasia and the Caucasus regions are no exception as the intensive flow of vehicles is there, as these are the areas of recreation and tourism. Primarily, the degree of resistance of zonal soils (forest, forest-steppe, steppe, and mountain-meadow soils) to Pb pollution was determined by the concentration of organic matter and the pH value. These indicators have a natural zonal character. Accordingly, it was interesting to study the geographical patterns of soil resistance to Pb contamination.
The aim of the present study was a comparative assessment of the resistance of soils in the forest, forest-steppe, steppe, and mountain-meadow areas of the Central Ciscaucasia and the Caucasus regions to Pb contamination and the development of the forecast maps for the deterioration of soils which will help to save the environment and the soil fertility by applying the possible control measures.

2. Materials and Methods

2.1. Objects of Study

The objects of study were forest—Rendzic Leptosols (Eutric), Greyic Phaeozems (Albic), Haplic Cambisols (Eutric); forest-steppe—Luvic Chernozems (Pachic), Greyzemic Chernozems (Pachic), Haplic Chernozems (Hyperhumic); steppe—Haplic Chernozems (Pachic); and mountain-meadow—Umbric Leptosols (Brunic), Umbric Leptosols (Dystric), Mollic Leptosols (Eutric) soils. The sampling sites and the main ecological and genetic characteristics of studied soils are given in Table 1.

2.2. Experimental Details

Laboratory modeling of chemical Pb contamination in the forest, forest-steppe, steppe, and mountain-meadow soils was carried out for the Central Ciscaucasia and the Caucasus regions. Earlier, Kolesnikov et al. [33,34] established the correctness of transferring the results of laboratory modeling of soil chemical pollution to the natural conditions.
The soil samples were taken from the upper layer, up to 20 cm deep, as the upper, most fertile soil horizons accumulate the maximum amount of Pb [35].
Lead was introduced into the soil in the form of PbO. Lead most often enters into the soil in the form of an oxide, where it gradually dissolves, to form complex compounds or cations [36,37]. The share of heavy metals entering the environment as oxides is 70%–80% [38].
In addition, while using a metal oxide, unlike salts, accompanying anions could only affect the biological properties of the soil without entering into the soil.
The concentration of the introduced PbO was 1, 10, 100 MPC or 100, 1000, and 10,000 mg/kg. The maximum concentration limit of Pb for soil in Russia has not been developed yet. According to hygienic standards, the approximate permissible concentrations for Pb in acidic soils (loamy and clayey) (pH < 5.5) is 65 mg/kg, neutral (loamy and clayey) (pH > 5.5)-130 mg/kg was reported [39].
The soil contaminated with PbO was incubated at optimal moisture and at the temperature 20 °C. The biological activity of soils was determined after 30 days of introduction of PbO. This period allows revealing the maximum toxicity of the metal and is most informative in experimental data analysis [40].
The studied biological parameters are highly sensitive and informative, and closely correlated between the parameter and the concentration of pollutants in the soils, which has been confirmed by numerous studies [34,40,41].

2.3. Determination of Soil Biological Parameters

Conventional methods in soil biology were used to determine the biological properties of the soil [34]. Laboratory studies of biological indicators have been performed using methods given below in Table 2.

2.4. The Calculation of Integral Parameter’s Indicator of Biological State (IIBS) of Soils

On the basis of above biological indicators, the integral indicator of the biological state (IIBS) of the soil was determined [42]. For the calculation of IIBS, the value of each of the above indicators for the control (in unpolluted soil) was taken as 100%, and relative to it, the percentages in other experimental variants (in polluted soil) were expressed as a percentage. For IIBS, maximum value of each index (100%) is chosen from array data, and in reference to this, value of this index was expressed for other variants of experiments bythe following Formula (1):
B 1 = B x Bmax × 100   %
where B1—the relative score of the indicator, Bx—the actual value of the indicator, Bmax—the maximum value of the indicator.
The integral index of the soil biological state is calculated bythe following Formula (2):
IIBS = B 1 Bmax × 100   %
where IIBS—the integral index of the soil biological state, B1—the relative score of the indicator, Bmax—the maximum value of the indicator.
During diagnosis of the contamination value of each index in non-contaminated soil, it was taken as 100%. With reference to its value of the same index, in the contaminated soil was expressed in percentage, and then the average value of 6 selected biological indicators for each experiment was determined. The obtained IIBS value was expressed as a percentage concerning the control (taking as 100%). The methodology used in the experiment allowed integrating the relative values of different indicators, which could not be integrated because they have different units of measurement.
The degree of sensitivity of biological indicators was assessed by the degree of decrease in the values of the biological indicator compared to the control. The more the value of the biological indicator decreased, the more sensitive this biological indicator from their respective control (100%).
The informative value (informativeness) was assessed by the tightness of the correlation between the biological indicator and the concentration of lead in the soil. The closer the correlation coefficient is to R = −1, the higher the information content of this biological indicator.

2.5. Calculation of Regional Standards for the Maximum Permissible Concentration (rMPC) of Lead

Regional standards for the maximum permissible concentration (rMPC) of total Pb in soils were calculated according to the degree of violation of the ecological functions of the soil. As it was established earlier [34,43], with an increase in the concentration of a heavy metal or other pollutant in the soil, the violation of ecological functions occurs in a certain sequence, and it is advisable to use IIBS as an indicator for the violation of one or another group of soil ecological functions. Thus, with a decrease in IIBS by less than 5%, there is no violation of soil functions; a decrease in IIBS values by 5%–10% indicates a violation of information functions; by 10%–25%, biochemical, physicochemical, chemical, and holistic; by more than 25%, physical.
Based on the values of IIBS of soils determined at different concentrations of Pb, regression equations were constructed that characterized the relationship between IIBS and the pollutant concentration in the soil. According to the regression equations, the concentrations of Pb in the soil were established, leading to a decrease in IIBS by 5%, 10%, and 25%, which diagnoses the violation of different groups of ecological functions of the soil. Because the most important ecological functions of the soil, which determines its fertility, are the chemical, physicochemical, biochemical, and integral functions. The concentration that reduces the IIBS by 10% should be taken as the MPC of Pb in the soil, which indicates a violation of these groups of functions.

2.6. Construction of Forecast Maps for Soil Deterioration

The forecast maps for soil deterioration in the Central Ciscaucasia and the Caucasus regions were constructed based on the results obtained for the degree of reduction in IIBS while contaminated with Pb at concentrations of 100, 1000, and 10,000 mg/kg using the distribution areas of these soils. The maps were created by the Quantum Geographic Information System (QGIS) program.

3. Results

In most of the cases of a Pb-contaminated area, a decrease was recorded in the studied biological parameters for the forest, forest-steppe, steppe, and mountain-meadow soils (Figure 1): the activity of the catalase and dehydrogenase, the total number of bacteria, the abundance of bacteria for the genus Azotobacter, the length of the radish roots, and the cellulolytic activity. The degree of deterioration in the biological parameters depends on the concentration of Pb in the soil.
The regional standards for the maximum permissible concentration (rMPC) of total Pb in forest, forest-steppe, steppe, and mountain-meadow soils was established with the help of the regression equations shown in Table 3. The calculated values reflect the dependence of the decrease in the IIBS values on the concentration of the pollutant in the soil, at which the groups of the ecological functions of the soils change. The most expedient method for the remediation of soils contaminated with Pb has also been presented as in Table 4, given below.
The stages of calculating the regional MPCs for the Pb in the soils:
  • According to the results of the calculation, the IIBS presents data for each concentration of Pb for each type of soil and the background metal content.
  • The construction of the functions in relation to the concentration and biological effect. The feature selection is focused on the highest affinity R → 1.
Among the calculated functions, the logarithmic function was chosen as it has the highest correlation coefficient (R → 1) (Table 3).
3.
The equation was used to calculate the maximum permissible content of Pb in violation of certain functions of the soils: low, medium, and high pollution.
To estimate the Pb concentration values responsible, we can use a regression equation describing the dependency of the IIBS fall on the pollutant fraction in the soil. Regression equations allow us to calculate the pollutant concentrations responsible for the degradation of particular groups of ecosystemic soil functions.
Based on the results obtained in the present study, forecast maps of the deterioration of the biological state of the forest, forest-steppe, steppe, and mountain-meadow soils of the Central Ciscaucasia and the Caucasus regions were developed during their contamination with 100, 1000, and 10,000 mg/kg of Pb.
The results obtained can be used to predict the degree of deterioration of the ecological and biological state of the soils to one degree or another while their contamination has one or another amount of Pb.
In Figure 2, the green color of the scale corresponds to a decrease in the IIBS from 0% to 10%, that is, the normal functioning of the soil (0%–5%) or the violation of a group of information functions (5%–10%), which are not critical for the soil [34]. The yellow color corresponds to a decrease in the IIBS from 10% to 25%, that is, a violation of an additional group of chemical, physico-chemical, biochemical, and integral functions of the soil. The red color indicates an unacceptable decrease in the IIBS by more than 25%, that is, a violation of all groups of ecosystem functions, including physical ones. Next, the colors were applied to the contours of the areas of the corresponding soils studied.
For example, in Figure 2, in the case of Haplic Chernozems (Pachic) with 100 mg/kg of Pb contamination, its biological state deteriorates by 6%, 1000 mg/kg—by 15%, while in 10,000 mg/kg—22%. And in the case of contamination of the Haplic Cambisols (Eutric) with 100 mg/kg of Pb, its biological state deteriorates by 21%, 1000 mg/kg—by 34%, whereas in 10,000 mg/kg—54%.

4. Discussion

During the study, several forests, forest-steppe, steppe, and mountain-meadow soils were constructed according to the degree of resistance to Pb contamination (in brackets there are the values of the average for three doses: 1, 10, and 100 MPC; the soils are arranged as their resistance decreases): Luvic Chernozems (Pachic) (88) ≥ Greyzemic Chernozems (Pachic) (86) = Haplic Chernozems (Pachic) (86) > Rendzic Leptosols (Eutric) (80) ≥ Haplic Chernozems (Hyperhumic) (79) ≥ Mollic Leptosols (Eutric) (78) > Greyic Phaeozems (Albic) (75) ≥ Umbric Leptosols (Dystric) (72) ≥ Umbric Leptosols (Brunic) (71) > Haplic Cambisols (Eutric) (64).
The resistance of the studied soils to Pb contamination is determined by the ecological and genetic characteristics, namely the granulometric composition, alkaline acid conditions, and the concentration of organic matter, as shown in Table 1. Similar patterns were obtained for other soils in the south of Russia: mountainous [48], coastal [49], and arid [50]. Such patterns are characteristic of soil contamination not only with lead but also with other heavy metals. For example, cadmium [51], copper [52], silver [53], and bismuth [54].
Lead in the soil becomes more mobile and exhibits a greater toxicity with an increase in the acidity of the soil environment [36,55], an increase in the proportion of the heavy fraction of the granulometric composition [56,57], and the content of organic matter in the soil [36,37]. At the same time, soil pH is much more important than the content of organic matter [58].
The most resistant soils to Pb contamination were Luvic Chernozems (Pachic), Greyzemic Chernozems (Pachic), and Haplic Chernozems (Pachic) to a greater extent, while Haplic Chernozems (Hyperhumic) was to a lesser extent. The characterization was performed by a heavy granulometric composition, a close to neutral reaction of the environment, and a relatively high concentration of organic matter. All these factors contribute to the consolidation of the Pb in the soil. Luvic Chernozems (Pachic) were the most stable. They have the heaviest granulometric composition, a relatively high pH, and a high concentration of organic matter [46].
Rendzic Leptosols (Eutric) have a heavy granulometric composition, a neutral pH, due to the high content of carbonates, which reduces the mobility of Pb [8], but contain less organic matter, which increases the mobility of Pb in these soils compared to Chernozems.
Mollic Leptosols (Eutric) and Umbric Leptosols (Dystric) have a neutral reaction in the environment and a high concentration of organic matter; however, according to the granulometric composition, the soils are medium loamy, which reduces the resistance to contamination.
Greyic Phaeozems (Albic) were also found to be close to Chernozems in granulometric composition. The concentration of organic matter is even higher, because unlike plowed Chernozems, these soils are located under the forest. However, the reaction of the environment is more acidic than in Haplic Chernozems (Pachic), Luvic Chernozems (Pachic), and Rendzic Leptosols (Eutric). This determines that these soils have a somewhat lower resistance to Pb contamination when compared with Chernozems and Leptosols.
Umbric Leptosols (Brunic) are distinguished by a high concentration of organic matter but have an acid reaction to the environment and a medium loamy granulometric composition. As a result, their resistance to contamination is similar to that of Greyic Phaeozems (Albic).
The poorly unsaturated Haplic Cambisols (Eutric) showed the least resistance to Pb contamination because of the slightly alkaline reaction of the medium, which increases the mobility of Pb. This factor is not compensated even by a relatively high organic matter concentration.
Thus, all forest-steppe and steppe soils showed a high and very high resistance to Pb contamination due to a greater pH and heavier granulometric composition; mountain-meadow soils showed a high and average resistance because of the higher organic matter content but lower pH values and less heavy granulometric composition; forest soils showed high Rendzic Leptosols (Eutric) due to the higher pH due to the high content of carbonates, average Greyic Phaeozems (Albic) because of a more average pH, and the least resistance in the Haplic Cambisols (Eutric), that is, the largest variation in the resistance to Pb contamination due to a significantly more acidic pH among all the soils.
The results obtained testify to the high sensitivity and information concentration of the studied biological indicators and the possibility of their application to assess the resistance of forest, forest-steppe, steppe, and mountain-meadow soils to Pb contamination.
Previously used biological indicators performed well on the soils of dry steppes and semi-deserts [59], including saline soils [60].
The concentration of Pb, which causes a violation of the integral ecological functions of the soil, determines that its most important properties, including fertility, should be taken as the rMPC. As shown in Table 3, if, for example, in Haplic Chernozems (Pachic) the Pb concentration does not exceed 65 mg/kg, then the soil functions normally, and remediation is not required.
If the Pb concentration is from 65 to 150 mg/kg, the informational ecological functions of the soil will be disturbed. The necessary remediation methods, such as the re-profiling of industries and the selection of agricultural crops that reduce the mobility of Pb, could be applied. The cultivation of root and tuber crops, fodder grain, perennial grasses for seeds, and flowers can be performed while carrying out the necessary agrochemical measures.
At a contamination level from 150 to 500 mg/kg, in addition to information, the chemical, physicochemical, biochemical, and complete functions will be violated. At this level of contamination, plowing to a depth of 30 cm will be required with the application of organic fertilizers and lime. Liming is the main way to reduce the mobility of Pb in acidic soils. It is recommended to apply a dose of lime fertilizer that will bring the pH to a level of 6.5 to 6.7.
At more than 500 mg/kg, a disruption of the physical functions of the soil will occur. With this level of contamination, cardinal methods of remediation are necessary, namely the use of plantation, plows, and special equipment—scrapers and graders to remove the contaminated soil layer.
Consequently, the higher the Pb in the soil, the more “radical” the method of remediation would need to be applied. The Pb concentration of 150 mg/kg should be considered the maximum permissible concentration (MPC) of Pb in Haplic Chernozems (Pachic) or the regional MPC (rMPC).
In the territory of the Central Caucasus, there is one of the largest non-ferrous metallurgy enterprises in Russia—the Electrozinc plant (Vladikavkaz city). A metallurgical enterprise is a source of catastrophic pollution of the environment with Pb, exceeding the regional Clarks of Pb in the soils [61,62] by dozens of times [63]. As could be observed in the results of the present study, such Pb content causes a disruption in all the groups of the soil ecosystem functions (Table 4), which means a catastrophic disruption of the soil functioning [22,34,43].

5. Conclusions

The forest, forest-steppe, steppe, and mountain-meadow soils of the Central Ciscaucasia and the Caucasus regions showed different resistance patterns to Pb contamination. All the forest-steppe and steppe soils showed a high and very high resistance to Pb contamination, the mountain-meadow soils showed a high and average resistance, and the forest soils showed a high (Rendzic Leptosols (Eutric), average (Greyic Phaeozems (Albic), and the least resistance (Haplic Cambisols (Eutric), that is, the largest variation in resistance. The number of studied soils was built according to the degree of resistance to Pb contamination: Luvic Chernozems (Pachic) (88) ≥ Greyzemic Chernozems (Pachic) (86) = Haplic Chernozems (Pachic) (86) > Rendzic Leptosols (Eutric) (80) ≥ Haplic Chernozems (Hyperhumic) (79) ≥ Mollic Leptosols (Eutric) (78) > Greyic Phaeozems (Albic) (75) ≥ Umbric Leptosols (Dystric) (72) ≥ Umbric Leptosols (Brunic) (71) > Haplic Cambisols (Eutric) (64). The heavier the particle size distribution, the more organic matter, and with a pH close to neutral in the studied soils, the stronger the binding of metals and the less ecotoxicity.
The regional maximum permissible concentrations (rMPC) of Pb in the forest, forest-steppe, steppe, and mountain-meadow soils have been developed based on the violation of their ecosystem functions. The rMPC for the Pb Luvic Chernozems (Pachic), Greyzemic Chernozems (Pachic), and Haplic Chernozems (Pachic) is 150 mg/kg; for the Rendzic Leptosols (Eutric), Haplic Chernozems (Hyperhumic), and Mollic Leptosols (Eutric)—140 mg/kg; for the Greyic Phaeozems (Albic)—130 mg/kg; for the Umbric Leptosols (Dystric) and Umbric Leptosols (Brunic)—120 mg/kg; and for the Haplic Cambisols (Eutric)—100 mg/kg.
The schematic forecast maps of the deterioration of the biological state of the main soils of the Central Ciscaucasia and the Caucasus regions was developed during the contamination with different concentrations of Pb. That gives an idea about the degree of deterioration of the soils and the biological state of the studied soils which could be avoided by applying some remediation approaches to save the earth/soil quality.

Author Contributions

Conceptualization, S.I.K.; data curation, D.I.M., A.A.K., K.S.K. and V.P.K.; formal analysis, D.I.M. and A.A.K.; funding acquisition, T.M.M.; investigation, S.I.K., K.S.K. and S.S.S.; methodology, A.A.K., K.S.K. and A.A.M.; project administration, T.M.M. and S.S.M.; resources, S.S.M.; software, K.S.K., A.A.M. and Y.A.L.; supervision, S.I.K., T.M.M., S.S.M. and S.N.S.; validation, Y.A.L., S.N.S. and V.P.K.; visualization, A.A.M., Y.A.L. and S.S.S.; writing—original draft, D.I.M.; writing—review and editing, T.M.M. and S.S.S. All authors have read and agreed to the published version of the manuscript.

Funding

The study was carried out in the laboratory «Soil Health» of the Southern Federal University with the financial support of the Ministry of Science and Higher Education of the Russian Federation, agreement no. 075-15-2022-1122, and the Strategic Academic Leadership Priority of the Southern Federal University («Priority 2030»), SP-12-22-10, IP-212-21-16.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Forests 13 01528 g001a 550Forests 13 01528 g001b 550Forests 13 01528 g001c 550Forests 13 01528 g001d 550
Figure 1. The effect of lead (Pb) contamination on the biological parameters of forest, forest-steppe, steppe, and mountain-meadow soils (% of control): (A)—the catalase activity, (B)—the activity of dehydrogenases, (C)—total number of bacteria, (D)—the abundance of bacteria of the genus Azotobacter, (E)—the phytotoxic properties (length of radish roots), (F)—the cellulolytic activity, (G)—the integral indicator of the biological state (IIBS).
Figure 1. The effect of lead (Pb) contamination on the biological parameters of forest, forest-steppe, steppe, and mountain-meadow soils (% of control): (A)—the catalase activity, (B)—the activity of dehydrogenases, (C)—total number of bacteria, (D)—the abundance of bacteria of the genus Azotobacter, (E)—the phytotoxic properties (length of radish roots), (F)—the cellulolytic activity, (G)—the integral indicator of the biological state (IIBS).
Forests 13 01528 g001aForests 13 01528 g001bForests 13 01528 g001cForests 13 01528 g001d
Forests 13 01528 g002a 550Forests 13 01528 g002b 550
Figure 2. Forecast maps of the degree of deterioration of the biological state (in %) of forest, forest-steppe, steppe, and mountain-meadow soils of the Central Ciscaucasia and the Caucasus regions during their pollution: (A)—100 mg/kg, (B)—1000 mg/kg, (C)—10,000 mg/kg of lead (Pb). Symbols: 1—Haplic Chernozems (Pachic), 2—Luvic Chernozems (Pachic), 3—Greyzemic Chernozems (Pachic), 4—Haplic Chernozems (Hyperhumic), 5—Rendzic Leptosols (Eutric), 6—Greyic Phaeozems (Albic), 7—Haplic Cambisols (Eutric), 8—Umbric Leptosols (Brunic), 9—Leptosols (Dystric), 10—Mollic Leptosols (Eutric).
Figure 2. Forecast maps of the degree of deterioration of the biological state (in %) of forest, forest-steppe, steppe, and mountain-meadow soils of the Central Ciscaucasia and the Caucasus regions during their pollution: (A)—100 mg/kg, (B)—1000 mg/kg, (C)—10,000 mg/kg of lead (Pb). Symbols: 1—Haplic Chernozems (Pachic), 2—Luvic Chernozems (Pachic), 3—Greyzemic Chernozems (Pachic), 4—Haplic Chernozems (Hyperhumic), 5—Rendzic Leptosols (Eutric), 6—Greyic Phaeozems (Albic), 7—Haplic Cambisols (Eutric), 8—Umbric Leptosols (Brunic), 9—Leptosols (Dystric), 10—Mollic Leptosols (Eutric).
Forests 13 01528 g002aForests 13 01528 g002b
Table
Table 1. Sampling locations and ecological and genetic characteristics of studied soils.
Table 1. Sampling locations and ecological and genetic characteristics of studied soils.
No.Name of Soils According to Ecological and Genetic Classification [31]Name of Soils World Reference Base (WRB) for Soil Resources [32]Place of SelectionCoordinatesContent of Organic Matter, %pHGranulometric Composition
1Chernozems ordinaryHaplic Chernozems (Pachic)Stavropol Territory, Kochubeevsky district, the village of Kochubeevskoe44°36′12.48″ C, 41°50′26.30″ B4.57.1Light clay
2Chernozems leached (mountain)Luvic Chernozems (Pachic)Karachay-Cherkess Republic, Khabez District, aul Ali-Berdukovsky43°57′53.78″ C, 41°43′36.21″ B46.9Heavy loamy
3Chernozems podzolized (mountain)Greyzemic Chernozems (Pachic)Karachay-Cherkess Republic, Khabezsky District, aul Kosh-Khabl44° 8′1.43″ C, 41°51′14.39″ B4.16.5Heavy loamy
4Chernozems typical (mountain)Haplic Chernozems (Hyperhumic)Stavropol Territory, Predgorny district, Yutsa village43°58′59.16″ C, 42°56′9.83″ B7.17.4Heavy loamy
5Sod-calcareousesRendzic Leptosols (Eutric)Karachay-Cherkess Republic, Zelenchuksky district, the village of Advanced44°06′26.42″ C, 41°25′22.27″ B3.27.1Heavy loamy
6Dark gray forestGreyic Phaeozems (Albic)Stavropol, reserve “Russian forest”45°02′37.58″ C, 41°52′51.68″ B5.66.5Heavy loamy
7Brown forest weakly unsaturatedHaplic Cambisols (Eutric)Karachay-Cherkess Republic, Karachaevsky urban district, Teberda43°23′11.06″ C, 41°42′20.32″ B7.74.9Heavy loamy
8Mountain-meadowsod-peatyUmbric Leptosols (Brunic)Karachay-Cherkess Republic, Karachaevsky urban district, the village of Dombai43°17′30.70″ C, 41°38′50.91″ B24.35.3Loamy
9Mountain-meadow soddyUmbric Leptosols (Dystric)Karachay-Cherkess Republic, Malokarachaevsky district, Kichi-Balyk village43°46′16.43″ C, 42°39′56.43″ B12.26.4Loamy
10Mountain-meadow chernozem-likeMollic Leptosols (Eutric)Kabardino-Balkarian Republic, Zolsky district, Dzhily-Su tract43°26′28.90″ C, 42°33′15.60″ B10.36.5Loamy
Table
Table 2. Characteristics of biological indicators of soil condition.
Table 2. Characteristics of biological indicators of soil condition.
No.Biological IndicatorsMeasure UnitMethodsNumber of Repetitions for One Soil
1Total number of bacteria109 bacteria in 1 g of soil dry weightLuminescent microscopy with solution of acridine orange, 40× [42](n = 720: 3 incubation vessels with soil × 3 soil samples × 4 square centimeters on object glass × vision fields)
2Azotobacter sp. abundance% of the mud balls surrounded by Azotobacter mucusThe method of fouling lumps on the Ashby medium [43](n = 241: 3 incubation vessels with soil × 3 soil samples in Petri dishes × 25 mud balls)
3Catalase activitymL O2 per gram of soil dry weight in 1 minBy the rate of decomposition of hydrogen peroxide [44](n = 36: 3 incubation vessels with soil × 3 soil samples × 4 analytic repetitions)
4Dehydrogenases activitymg of triphenyl formazane (TPF) per gram of soil dry weight for hourAccording to the rate of conversion of triphenyl tetrazolium chloride (TPC) to triphenyl formazane (TPF) [44](n = 36: 3 incubation vessels with soil × 3 soil samples × analytic repetitions)
5Cellulolytic activitymilligramsAccording to the degree of decomposition of cotton fabric [42](n = 9: 3 incubation vessels with soil × 3 cotton sheets)
6The length of radish (Raphanus sativus L.) rootsmillimetersThe measurement of the length of radish (R. sativus L.) roots after 7 days of treatment [43](n = 241: 3 incubation vessels with soil × 3 soil sample in Petri dishes × 25 radish seeds)
Table
Table 3. Regression equations describing the decrease in IIBS values from the content of Pb in the soil.
Table 3. Regression equations describing the decrease in IIBS values from the content of Pb in the soil.
Type of SoilRegression Equations
Haplic Chernozems (Pachic)/Chernozems ordinaryy = −3.957ln(x) + 113.49 R2 = 1
Luvic Chernozems (Pachic)/Chernozems leached (mountain)y = −3.139ln(x) + 109.98 R2 = 0.9782
Greyzemic Chernozems (Pachic)/Chernozems podzolized (mountain)y = −4.951ln(x) + 120.33 R2 = 1
Haplic Chernozems (Hyperhumic)/Chernozems typical (mountain)y = −3.407ln(x) + 109.32 R2 = 1
Rendzic Leptosols (Eutric)/Sod-calcareousesy = −4.944ln(x) + 114.61 R2 = 1
Greyic Phaeozems (Albic)/Dark gray foresty = −5.61ln(x) + 104.63
R2 = 1.00
Haplic Cambisols (Eutric)/Brown forest weakly unsaturatedy = −9.396ln(x) + 131.39 R2 = 1
Umbric Leptosols (Brunic)/Mountain-meadow sod-peatyy = −7.478ln(x) + 125.69 R2 = 1
Umbric Leptosols (Dystric)/Mountain-meadow soddyy = −8.809ln(x) + 134.14 R2 = 1
Mollic Leptosols (Eutric)/Mountain-meadow chernozem-likey = −6.082ln(x) + 120.72 R2 = 1
Table
Table 4. Regional standards for the maximum permissible concentration (rMPC) of Pb in forest, forest-steppe, steppe, and mountain-meadow soils according to the degree of violation of ecosystem functions and recommended methods for soil remediation.
Table 4. Regional standards for the maximum permissible concentration (rMPC) of Pb in forest, forest-steppe, steppe, and mountain-meadow soils according to the degree of violation of ecosystem functions and recommended methods for soil remediation.
Soils 1Not PollutedWeakly PollutedModerately PollutedStrongly Polluted
Degree of decline in IIBS of soil 2<5%5%–10%10%–25%>25%
The disturbed ecosystem functions 3Not ApplicableInformationalChemical, physico-chemical, biochemical; holisticPhysical
WRB/SoilLead (Pb) content in soil, mg/kg
Haplic Chernozems (Pachic)/Chernozems ordinary<6565–150150–500>500
Luvic Chernozems (Pachic)/Chernozems leached (mountain)<7070–150150–500>500
Greyzemic Chernozems (Pachic)/Chernozems podzolized (mountain)<7070–150150–500>500
Haplic Chernozems
(Hyperhumic)/Chernozems typical (mountain)		<5555–140140–450>450
Rendzic Leptosols (Eutric)/Sod-calcareouses<6565–140140–450>450
Greyic Phaeozems (Albic)/Dark gray forest<6060–130130–300>300
Haplic Cambisols (Eutric)/Brown forest weakly unsaturated<5050–100100–220>220
Umbric Leptosols (Brunic)/Mountain-meadow sod-peaty<5050–120120–250>250
Umbric Leptosols (Dystric)/Mountain-meadow soddy<9090–120120–250>250
Mollic Leptosols (Eutric)/Mountain-meadow chernozem-like<7070–140140–450>450
The most appropriate methods for the remediation of soils contaminated with leadRemediation is not requiredPhytoremediation, flushingChemical melioration: introduction of organic substances, ion exchange resins, phosphoric fertilizers, lime, zeolitesRemoval of contaminated soil and replacement with a new environmentally and agriculture-friendly soil
Note: 1 Classification of soils [45]; 2 Determination of IIBS of soils [46]; 3 Classification of ecosystem functions [47].
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Moshchenko, D.I.; Kolesnikov, S.I.; Kuzina, A.A.; Kazeev, K.S.; Minkina, T.M.; Mezhenkov, A.A.; Litvinov, Y.A.; Shende, S.S.; Mandzhieva, S.S.; Sushkova, S.N.; et al. Comparative Assessment of the Resistance to Lead (Pb) Pollution of Forest, Forest-Steppe, Steppe, and Mountain-Meadow Soils of the Central Ciscaucasia and the Caucasus Regions. Forests 2022, 13, 1528. https://doi.org/10.3390/f13101528

AMA Style

Moshchenko DI, Kolesnikov SI, Kuzina AA, Kazeev KS, Minkina TM, Mezhenkov AA, Litvinov YA, Shende SS, Mandzhieva SS, Sushkova SN, et al. Comparative Assessment of the Resistance to Lead (Pb) Pollution of Forest, Forest-Steppe, Steppe, and Mountain-Meadow Soils of the Central Ciscaucasia and the Caucasus Regions. Forests. 2022; 13(10):1528. https://doi.org/10.3390/f13101528

Chicago/Turabian Style

Moshchenko, D. I., Sergey I. Kolesnikov, A. A. Kuzina, Kamil S. Kazeev, Tatiana M. Minkina, A. A. Mezhenkov, Y. A. Litvinov, Sudhir S. Shende, Saglara S. Mandzhieva, Svetlana N. Sushkova, and et al. 2022. "Comparative Assessment of the Resistance to Lead (Pb) Pollution of Forest, Forest-Steppe, Steppe, and Mountain-Meadow Soils of the Central Ciscaucasia and the Caucasus Regions" Forests 13, no. 10: 1528. https://doi.org/10.3390/f13101528

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