Degradation of soils as a result of human-induced transformation of their water regime and soil-protective practice

82

ISSN 1064-2293, Eurasian Soil Science, 2009, Vol. 42, No. 1, pp. 82–92. © Pleiades Publishing, Ltd., 2009.Original Russian Text © F.R. Zaidel’man, 2009, published in Pochvovedenie, 2009, No. 1, pp. 93–105.

GENERAL ASPECTS

The state and development of human society aredetermined to a great extent by its relations with theenvironment. Positive and negative consequences ofappropriate or irrational use of natural resources arewell known. Not only countries but also civilizations onthe Earth were destroyed owing to the tragic distur-bance of permanent natural laws by human economicactivities. Odum [19] stated that “…a human best liveswhen he acts as part of nature…otherwise, like anunreasonable parasite, he can use his host in such a waythat risks destroying himself” (p. 130). Current practicepresents many rather bright examples that support thisstatement. The pool of known data allows recognizingthat natural laws should be taken into account in anyinteraction with nature, particularly in the implementa-tion of ameliorative projects. D.L. Armand, an out-standing specialist in landscape science, emphasizedthat … the way worthy of people is not to endlesslyconquer nature but to arrange peaceful coexistence withit. For this purpose, people should learn to consumerenewable natural resources in amounts not more thanthey can reproduce and to throw out no more waste thanthey can return to the useful natural turnover [2, p. 274].

In order to classify, forecast, and prevent undesiredevents and substantiate a system of soil and landscapeprotection against human-induced degradation, it isnecessary to first of all reveal the causes of the degrada-tion. The principal reasons for soil degradation are notnumerous and are due to the action of hydrological,chemical, radiological, and mechanical factors. Amongthe factors mentioned, the role of the hydrological fac-

tor responsible for many destructive phenomena is theleast understood.

At the same time, the soil degradation because ofhuman-induced changes in the hydrological regimes isclosely related to secondary soil-forming processes thathave recently became widespread due to large-scalehydraulic engineering, amelioration, the effects of roadconstruction on the water regime, and so on. Previ-ously, the author considered the role of the hydrologicalfactor on the anthropogenic degradation of soils in theRussian Federation [4]. This paper concerns the soildegradation in different natural zones of the Earth dueto changes in their water regime; it is based predomi-nantly on the results obtained by the author and sum-marizing the literature data as well.

The main attention is paid to the soil degradationdue to changes in the water regime under the influenceof large-scale hydraulic engineering, amelioration(drainage, irrigation) of agricultural lands, use of inad-equate agronomic procedures, road building, and so on.Thus, all the kinds of soil degradation presented in thisarticle are related to changes in the soil water regimedue to the intense water economic practice. Consider-ing each kind of soil degradation, the author intended toanswer the following questions: (1) What is the reasonfor soil degradation? (2) How is degradation displayed?(3) How do we protect soil against dangerous soil deg-radation? Thirty cases of soil degradation are consid-ered below. In the context of this article, one can onlyoutline the character of changes in soils resulting fromhuman activity and suggest some preventive measuresagainst their degradation. A more detailed characteriza-tion of phenomena leading to soil degradation induced

Degradation of Soils as a Result of Human-Induced Transformation of Their Water Regime and Soil-Protective

Practice

F. R. Zaidel’man

Faculty of Soil Science, Moscow State University, Moscow, 119991 RussiaE-mail: [email protected]@

Received January 24, 2008

Abstract

—The adverse human-induced changes in the water regime of soils leading to their degradation areconsidered. Factors of the human activity related to the water industry, agriculture, and silviculture are shownto play the most active role in the soil degradation. Among them are the large-scale hydraulic works on rivers,drainage and irrigation of soils, ameliorative and agricultural impacts, road construction, and uncontrolledimpacts of industry and silviculture on the environment. The reasons for each case of soil degradation relatedto changes in the soil water regime are considered, and preventive measures are proposed. The role of secondarysoil degradation processes is shown.

DOI:

10.1134/S1064229309010116

DEGRADATION, REHABILITATION, AND CONSERVATION OF SOILS

EURASIAN SOIL SCIENCE

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DEGRADATION OF SOILS AS A RESULT OF HUMAN-INDUCED 83

by changes in the water regime can be found in the ref-erences given in this article when analyzing each indi-vidual kind of degradation. The kinds of soil degrada-tion are presented in the table.

KINDS OF SOIL DEGRADATION, THEIR CHARACTERISTICS AND DIAGNOSTICS,

AND PREVENTIVE PROCEDURES

Hydraulic engineering constructions are powerfuland fast-acting factors causing changes in the hydrolog-ical regime of soils (table, 1). On plains, soil degrada-tion is frequently related to large water reservoirs, theareas of which are formed by shallow- and deep-watersubmerged zones (table, 1.1). Shallow water areas arelarge peripheral parts of water reservoirs with a waterlayer <3 m. These vast areas accumulate insignificantwater volume weakly affecting the work of hydroelec-tric power stations. Shallow places of plain water reser-voirs are floodplain terraces with initially fertile soils.The flooded forests and shrubs prevent the developmentof a fishery and the work of water transport. Theflooded soils of these shallow sites, unlike the soils ofdeep-water areas, are not covered with unfertile graysilt after being under water for a long time. They remainhighly fertile even after drainage and can be used inagriculture [10, 17]. In the forest and forest-steppezones, these soils may be used under conditions ofpolder drainage and effective fertilization. In the steppeand semidesert zones, the reclamation of soils may becomplicated by their secondary salinization.

Waterlogging of the soils in a water reservoir head-race (table, 1.2) is a reason for their bogging in the for-est and forest-steppe zones; it is a reason for boggingand salinization in the more southern regions. However,in the future, these soils may be a substantial and, insome regions, single source of replenishing the area ofnew agricultural lands.

In the first case, the degree of water logging and adifferentiated approach should be taken into accountwhile choosing alternative solutions. Natural meadowsor croplands with field crop rotations composed ofcrops resistant to water logging may be created onweakly bogged soils. The expediency of ameliorativemeasures can be estimated according to the “Instruc-tions on Diagnostics of Waterlogging of Mineral Soilsin the Nonchernozemic Zone of the Russian Federationand Assessment of the Expediency of Their Drainage(guide to BSN-33-2.1-84)” compiled by the author.

In the second case, in southern regions of our coun-try, in the headrace of reservoirs, bogging and saliniza-tion of soils are possible. Drainage and measures forsoil desalinization may prevent the soil degradation [6].

Presently, in southern European Russia, mainly inRostov oblast and Stavropol and Krasnodar regions, thegroundwater table is rising quickly and bogging, salin-ization, solonetzization, compaction, and gley pro-cesses are enhanced by intense hydraulic engineering

construction (1.3). A real danger of these processes istheir adverse effect up to destruction of the best soils inour country (ordinary and southern chernozems, darkchestnut, and other soils) owing to the formation ofmochar (waterlogged) landscapes. Hence, on crop-lands, these fertile soils are substituted for weakly fer-tile or infertile gleyed, compact, saline, solonetzic soils.The conditions of their formation, agroecology, andamelioration were investigated earlier [13]. Two cir-cumstances are responsible for the appearance of mochariclandscapes in the steppe zone. First, is the replacement ofdroughty climatic periods by 11- to 13-year-long periodswith moist summers. Second, a drastic increase in theinflow of infiltration water to the groundwater and adecrease in the thickness of the aeration zone take placedue to hydrotechnical works—the creation of largewater reservoirs, many water bodies of economic usewithin the region, dense irrigation networks, and so on.Since the enclosing and waterproof sediments aresaline, the infiltrating fresh water is transformed intosaline, and the upward flow of the water carries greatamounts of salts (mainly, sodium sulfates and chlo-rides) to the surface. These phenomena can be observedin the areas composed of Maikop deposits. However,water logging is the leading factor of soil degradationthere. Therefore, artificial drainage is the first measurefor the restoration of the soil fertility; then, a complexof procedures for desalinization; desolonetzization; andelimination of vertic, solodic, and alkalinization fea-tures should be used [6].

Along with hydraulic engineering construction,ameliorative practices (in particular, drainage) (table, 2)play a significant role in the degradation of soilsbecause of the negative changes in their water regime.The adverse effect of ameliorative measures on soilsappears in the cases when they cause deep lowering ofthe groundwater table and separation of the capillaryfringe from the peat layer. This phenomenon takesplace upon deep drainage of low moors (table, 2.1, a).This method of drainage was widespread in the early1960s [1]. In the author’s opinion, the expected effectcan be reached upon gravity drainage with the use ofdeep canals (3.5 to 5.0 m). This deep drainage was rec-ommended for peat soils underlain by sand, i.e., forbogged woodland sandy areas (polesie landscapes).However, soon after the drainage of low-moor peatsoils by deep canals, practically everywhere their quickdegradation began. At that time, we wrote (based on ourobservations) that an obligatory consequence of this“amelioration” would be the destruction of landscapesand soils by all means [3]. Unfortunately, this forecastproved to be justified. The deep drainage of the organicsoils in the southern taiga of European Russia hascaused dangerous dehydration of peat and landscapes,accelerated the biochemical decomposition of peatorganic matter, and caused fires and wind erosion. Afterthe complete peat depletion, infertile or weakly fertilerocks (gleyic quartz sands, lime, and marl horizons)outcropped. In the course of the peat organic matter

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Degradation of soils resulting from human-induced changes in their hydrological regime and preventive measures for soilcontrol

no.* Causes of soil degradation Degradational changes of soils Preventive measures against soil degradation

1. Hydrotechnical

1.1 Flooding of soils in shallow zones of water reservoirs in the plains

Intense bogging predominantly by fresh water

Organization of polder drainage–irrigation systems

1.2 Underflooding of soils in the headrace of water reservoirs

Waterlogging and/or salinization of soils

Drainage and measures for desalinization of saline soils

1.3 Waterlogging; water logging and salinization of automorphic soils of rain-fed territories due to a rise of the table of mineralized groundwater entering the adjacent areas from irrigation systems and water reservoirs

Formation of mochars. Secondary water logging and salinization of chernozems. Formation of saline and nonsaline meadow and chernozem–meadow soils among chernozems

Drainage, vertical antifiltration grouting, networks of trap canals, snow retention, and desalinization and desolonetzization of saline soils

2. Ameliorative (drainage objects)

2.1 Periodic or permanent (under deep drainage) disjoining of the groundwater table from the drained peat soil layers under gravity-flow drainage

(a) Accelerated decomposition of organic matter and peat, (b) Total pyrogenic destruction of drained peat soils

Creation of the meadow type of water regime of soils. Grass sowing or crop rotations with grasses. Cover or mixed sanding. Organic fertilizers for maintenance of the carbon budget. Fire-prevention measures. Sprinkling

2. 2 Gravity-flow drainage of peat soils with the use of cultivated crop rotations and heavy machinery

Accelerated decomposition of peat organic matter under normalized drainage

Maintenance of the meadow type of water regime, use as green lands (meadows, meadow or meadow–pas-ture crop rotations), application of organic fertilizers, plowing of stubble remains, and fire control. The use of vehicles with a low pressure on the soil (<100 kPa)

2.3 Dehydrating effects of gravity-flow drainage systems in polesie and floodplains on soils of adjacent nonameliorated catchments

Desiccation of soils of adjacent catchments, including waterlogged soils due to gravity-flow drainage

Taking into account the effects of irrigation systems on nondrained catchment areas in designing them

2.4 Drainage of structural floodplain gleyed soils in row-crop rotations using heavy vehicles

Strong soil compaction; formation of perched water on very compact subsoil horizons

Crop rotations with grasses; lowering of vehicles' pressure on soils to 100 kPa. Application of organic fertilizers and liming of acid soils. Loosening to a depth of 50 cm, mole trenching, or chiseling

2.5 Deep ameliorative loosening of drained low-moor peat soils

Accelerated biochemical decomposition of peat organic matter

Rejection of deep ameliorative loosening; its substitution for mole trenching is possible

2.6 Deep ameliorative loosening of drained heavy-textured soils on fine-stratified varved clays

The physical properties of the soils and their water regimes are not improved

Rejection of deep ameliorative loosening; its substitution for measures concerning the surface runoff acceleration

2.8 Secondary rising of the iron-enriched groundwater table as a result of drains plugging with iron hydroxides and cessation of the drainage system functioning

Secondary water logging by groundwater with a high content of ferrous iron

Protection of drains against plugging by iron hydroxide (washing of drains, increasing their inclination gradient, use of iron bacteria inhibitors, use of drains of large diameter and trap canals)

2.9 Transformation of the stagnant water regime into the stagnant–percolative one under drainage of neutral or acid soils enriched in pyrite

Aeration of considerable amounts of pyrite with the formation of sulfuric acid and extra-acid soils

Arrangement of a surface water dis-charge network and ridges for efficient washing of soils of sulfuric acid by tropical rains with the following grow-ing of acid-tolerant plants (pineapple, eggplant, etc)


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Table.

(Contd.)


2.10 Transformation of the stagnant water regime into the stagnant–percolative one under drainage of soils on acid or neutral rocks

Intense leaching of Ca, Mg, Fe, Al, Mn, organic substances, and clay. Formation of podzolic horizons or an increase in their thickness

Liming, application of mineral and organic fertilizers, and grasses in crop rotations. Measures for the acceleration of the surface and soil runoff

3. Ameliorative (irrigation) objects

3.1 Transformation of the percolative water regime into the stagnant–perco-lative one under irrigation of soils with fresh water in the background of frequent excessive watering

The same as 2.10, the appearance of podzolic horizons

The same as 2.10, optimization of the watering regime

3.2 Prolonged periodic flooding of loamy soils of rice pads in the background of noticeable infiltration

Acidification and gleying of soils under a stagnant–percolative water regime. Leaching of alkali-earth metals, iron, manganese, and other elements. Podzolization or formation of “rice podzols” is possible

Drainage. Liming. Grasses in crop rotations. Aeration of the soil profile

3.3 Prolonged flooding of heavy-textured soils in rice paddies in the absence of visible infiltration

Acidification and gleying under a stagnant water regime

Drainage. Deep loosening. Grasses in the crop rotations. Liming (on acid and leached rocks)

3.4 Rise of the mineralized groundwater table resulting in salinization of soils

Accumulation of toxic salts in the rhizosphere. Secondary salinization

Measures for desalinization in the background of drainage

3.5 Rise of the mineralized (alkaline) groundwater table resulting in solo-netzization of soils

Accumulation of sodium in the exchange complex. Secondary solonetzization

Measures for desolonetzization in the background of drainage. Gypsum application, acidification, application of high doses of organic fertilizers, and sowing of grasses

3.6 Shallow groundwater table in irrigated areas

Formation of a thick compact horizon filled with dolomite

Deep ameliorative loosening. Creation of anaerobic conditions in the surface horizons by application of organic matter capable of fermentation; flooding of soils in the background of drainage

3.7 Stagnation of washing water in the upper horizons of heavy-textured gypsum-containing soils (with a considerable amount of large gypsum crystals)

Waterlogging of soils Effective methods of amelioration and use of soils for irrigated farming are not elaborated. At this stage, to use these soils in agriculture is inexpedient

3.8 Subsidence in soils enriched with fine-crystalline gypsum in irrigated areas along canals

Disturbance of the irrigation regime; insufficient watering; losses of the yield and irrigation water; and, probably, secondary salinization

Detailed survey for the compilation of maps of the gypsum content and its forms in soils along canals. Preliminary soaking of soils in areas dangerous in relation to subsidence, and elimination of suffusion funnels. Drainage for protection of soils against secondary water logging and salinization

3.9 Plowing and irrigation of skeletal soils (pebble alluvium at depths of 0–20 cm)

Destruction of the shallow fertile fine-earth soil layer

Skeletal soils should not be used in agriculture. The best kind of their use is for rain-fed pastures

3.10 Formation of mudflows under surface irrigation of loess soils of adyrs

Destruction of the soil cover and landscape of adyrs

Farming under sprinkling using small doses or drop irrigation of gardens and vineyards

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Table.

(Contd.)


4. Land improvement

4.1 Excessive moistening of nondrained gleyic heavy soils due to deep ameliorative loosening

Secondary water logging under a stagnant water regime. Compaction, disaggregation, and a drastic decrease in filtration

Drainage

4.2 Intense desiccation of drained peat soils under different methods of sanding

Accelerated decomposition of peat organic matter

Controllable locking—subirrigation, sprinkling, organic fertilizers, grasses in crop rotations or use as a meadow

5. Agronomic

5.1 Strong compaction of soils by agricultural vehicles resulting in an increase of surface runoff and accumulation of water in depressions and their water logging

Compaction of the subsoil horizon Loosening to a depth of 50 cm or mole trenching; grasses in crop rotations or land use as meadows, use of vehicles with a pressure on the soil of <100 kPa

5.1 Washout of floodplains at bed areas of unregulated rivers because of cutting of forests (urema) and plowing of soddy stratified sandy soils

Destruction of soils in ridge floodplains, sand depositing on meadows and croplands in central and near-terrace floodplains

Preservation of urema forests at river bed areas of floodplains. Refusal of agricultural use of sandy soils in these areas

6. Road–building

6.1 Excessive moistening of soils resulting from crossing of natural stream tracks (surface and groundwater) by highways, railways, runways of airports, dams, etc.

A. WaterloggingB. Waterlogging and salinization of soils

A. Holes in road dams, polders on large areas, collector–drainage systemsB. The same as 6.1.A and measures for desalinization of soils

7. Industrial (effects of mining, agriculture, and industry)

7.1 Underflooding and water logging of soils resulting from lowering of the hypsometric level of the surface in mining areas

Waterlogging Elevation of the surface by addition of earthy material or inwashing of dredged deposits. Coulisse designing

7.2 Flooding of soils owing to systematic discharge of waste water from different work sources (mines, open-cast mines), municipal waste water or water from cattle-breeding farms, etc., on conjugated areas

Waterlogging or, more rarely, water logging and salinization of soils

Creation of filter beds, decrease of the runoff volume, watering of perennial and annual plants with waste water. Accumulation of waste water in reservoirs

8. Landslides produced by uncontrolled cutting of forests on slope

s

8.1 Saturation of sand–ground bodies with water on slopes due to cessation of evapotranspiration after cutting of forests and their slipping down

Drastic drops of fertility of soils and their destruction. Adverse changes in the landscape

Trap canals for interception of groundwater or perched water along the gliding plane. Drainage of slope waterlogged areas. Terracing of slopes. Arrangement of supporting (concrete or stone) constructions (flood bed)

* The first figure is the number of the section, and the second one is the kind of degradation changes related to the transformation of thehydrological regime of the soils.


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decomposition, a considerable amount of nitratesentered the groundwater and caused eutrophication ofstreams and water bodies.

In Russia, the method of gravity drainage of low-moors by deep canals has not received wide recognition.However, in Belarus, where, in the 1960s, deep drainagewas widely introduced into agricultural practice, in a shorttime (within 10–14 years after the drainage systems wereput into operation) more than 150 thousand hectares offertile low-moor peat soils were destroyed. Their mainmassifs were lost for agriculture.

It is worth noting that the fast degradation and fulldisappearance of drained peat soils on amelioratedareas are possible not only in the background of deepdrainage but practically everywhere under an uncon-trolled regime of groundwater with a shallow gravitydrainage system (table, 2.1, b). These phenomena happenin the summer when the groundwater table is low. In thiscase, under the recurrent short-term (1.0–1.5 months) dis-connection of the capillary fringe and the peat layer, thelatter may burn fast. In drained bogs, unlike nondrainedones, fires lead to full burning out of the peat down tothe mineral bottom. In the course of peat burning, vari-ous pyrogenic formations appear, often with high initialalkalinity (pH 10–11). The territory of burned bogs islittle suitable for agricultural use. First, they lose theirorganic horizons and fertility; second, owing to thelowering of the hypsometric surface level, they areexposed to secondary bogging [22]. The latter is pre-dominantly observed in the areas of secondary pyro-genic–mucky and pyrogenic–sandy formations. Sincepeat usually burns on relatively limited plots (50–150 ha)within the total area of drained fertile peat soils, thelocal drainage of waterlogged pyrogenic formations onwell permeable sands immediately lowers the ground-water table and creates favorable conditions for spread-ing of fires over the whole drained area with low-moorpeat soils. Thus, the drainage of waterlogged pyrogenicformations may be a reason for the overall fires ondrained peat soils of bogged polesie landscapes. Thepreventive procedures are as followings. The deepgravity drainage of peat soils on sands should beceased. The drained peat soils should have a meadowtype of water regime. In any case, the separation of thegroundwater table from the peat layers is inadmissible.On these soils, sustainable expenses of organic mattershould be supported. Therefore, the formation of mead-ows on drained peat soils is necessary as well as the appli-cation of rotations with a high proportion of perennialgrasses and plowing of stubble organic remains. Differentkinds of sanding are recommended in these cases.

Of special danger are measures that are related togravity drainage of peat soils and their involvement intorotations without grasses and saturation with row crops(potato, cabbage, corn) and use of heavy agriculturalvehicles (table, 2.2). Unfortunately, nowadays, thismethod of amelioration and use of drained peat soils isthe most widespread in European Russia. In this situa-

tion, the rates of the peat depletion due to the intensebiochemical destruction of the organic matter and someother reasons turn out to be maximal. Under the usualnorms of drainage, they reach 2–3 cm/yr and more. Inthis case, the use of organic soils in rotations with rowcrops and soil tillage by heavy machines should beavoided. It is necessary to maintain the meadow type ofthe soil water regime; grass sowing with application oforganic fertilizers, fire control, and sprinkling irrigationis the most promising way of using these soils.

In polesie landscapes, in floodplains, and in morainesandy areas with a sandy water-bearing horizon close tothe surface, all the landscape elements are closelyrelated in terms of their hydrological regime. Underthese conditions, the local lowering of the groundwatertable affects large areas causing dangerous dehydrationof the soils within the whole catchment (table, 2.3).Therefore, when planning drainage systems, their influ-ence on the soils of the adjacent catchments should betaken into account in order to avoid a dangerous fall ofthe groundwater table, dehydration, and degradation ofthe soils [9].

In humid landscapes, the most fertile and less stablemineral soils are aggregated soils of the river centralfloodplains and of depressions adjacent to river ter-races. However, drainage, cultivation of row crops inrotations, and monoculture cause a drastic deteriorationof the physical properties of these soils, their waterregime, and other adverse phenomena (table, 2.4). As arule, a waterproof horizon is fast formed in their pro-files, and perched water appears on its surface in theperiods of irrigation and precipitation. In this case, thedegradation control measures include an increase in theportion of grasses in crop rotations; the use of agricul-tural vehicles with low pressure on the soil (<100 kPa);the systematic application of organic and mineral fertil-izers and liming; and the mechanical destruction of thesecondary waterproof horizons by surface tillage, chis-eling, or mole trench digging.

Deep ameliorative tillage along with drainage is arelatively new method of soil drainage. It can fastchange unfavorable physical properties of soils andeliminate excessive moistening [6, 11]. However, it iswell to bear in mind that the use of this method for peatsoils (table, 2.5) will accelerate the biochemicaldecomposition of their organic matter. Therefore, it ismore expedient to replace tillage by mole trenching. Insoils on heavy thin-layer varved clays, agromeliorativemeasures for the acceleration of the intrasoil runoff arenot recommended because of their specific fabric: inthese soils, there is no response to measures aimed atimproving their physical properties (table, 2.6).

Evidently, the systems with trenchless plastic drain-age, drainage with ceramic drains, mole drainage, deepameliorative tillage, and mole trenching (table, 2.7) areinefficient for medium- and strongly stony soils withboulders >30 cm for the control of the water regime.

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The secondary bogging of drained mineral and peatsoils and their removal from agricultural use may becaused by the chemical properties of the groundwaterand the fast damage of ceramic drains and, especially,of plastic drains because of plugging of the contactsbetween the drains and perforation by iron hydroxide(table, 2.8). This phenomenon takes place while drain-ing soils in the nonchernozemic region with shallowdeposits of waterproof or water-containing rocks rich innonsilicate iron minerals (for instance, pyrite in Juras-sic clays) [6, 9]. The soils of the Yakhroma River flood-plain (Moscow oblast) can be an example of this typewhere the tile drainage system built in the 1960s brokedown by 70–75% in the early 1970s because of theplugging of drainage lines. This happened because, inthe survey and planning of the ameliorative system, thehigh amounts of ferrous iron in the groundwater werenot revealed and protection of the drains against plug-ging with the ochre was not made. However, these mea-sures are not complicated. First of all, an increase in theinclination gradient of the drains to 0.005–0.007 isneeded, as well as the inhibition of the iron bacterialactivity by the application of copper ions to the drain-age water, the use of trap canals for catching the iron-enriched groundwater, and washing of the drains usingspecial machines. In this case, the agronomic and agro-meliorative measures (liming, mole trenching, deeptillage, etc.) are directed at the elimination of the highsoil acidity and improvement of the soil aeration.

Of special importance for world agriculture are thedegradation changes in waterlogged sulfide soils aftertheir drainage and aeration (table, 2.9). These soils richin pyrite (iron sulfide) are widespread in coastal zonesand in deltas of large rivers in southeastern Asia. Here,under anaerobic conditions and a close sulfate ground-water table, the recurrent input of fine sedimentsremoved from red weathering crusts rich in iron, theinput of mangrove plant falloff, and the processes ofsulfate reduction and accumulation of considerablepyrite amounts proceed. Under anaerobic conditions,the latter process does not start until intense soil aera-tion, oxidation of sulfides and accumulation of sulfuricacid begin due to drainage, the advance of the delta tothe ocean, and some other causes [5, 8, 23]. As a result,the pH decreases to 2.8–3.5. To neutralize such greatcontinuously increasing amounts of sulfuric acid withlime is almost impossible. Therefore, for the timebeing, the single method of using these soils is washingof the upper soil layers of sulfuric acid with water dur-ing tropical rainfalls. For this purpose, a network ofshallow canals is constructed, and the soil surface isshaped as a system of high convex ridges (as Georgian“kvali” or Italian “bualyatsio”). On the ridges, cropsresistant to high acidity of soils (pineapple, eggplant,etc.) are planted.

The difficulties of cultivating soils with sulfidesalinization consist not only in the necessity of sulfuricacid removal. In the course of sulfate reduction, iron istransformed to its soluble bivalent form. In this form,

iron reacts with the anion of phosphoric acid. After oxi-dation, iron precipitates in the trivalent form unavail-able for plants. The retrogradation of phosphates takesplace, which complicates the cultivation of sulfidesoils. This is the reason that large massifs of sulfidesoils in densely populated regions of southeastern Asiaremain weakly developed or are not used in agricultureat all [5].

In the drained areas of the forest zone, significantsoil degradation may occur because of the changes inthe water regime of waterlogged soils after their drain-age (table, 2.10). The earlier (before amelioration) stag-nant water regime is substituted for the stagnant–perco-lative one. The author’s studies [5, 8, 9] show that suchchanges in the hydrological regime lead to the transfor-mation of the solid phase of drained mineral soils. Thetransition to the stagnant–percolate water regime firstcauses a deep change in the chemical properties ofsoils—an increase in acidity and removal of Mn, Fe,Ca, Mg, and Al. The conditions for lessivage arise; thebase saturation and specific surface decrease, and thethickness of the light acid eluvial (podzolic) horizonsincreases. The latter may appear in profiles of earliernonpodzolized soils. These degradation phenomena areenhanced by the low level of agrotechnology. There-fore, it is not accidental that recently some informationappeared that, after drainage, in gleyic and gley mineralsoils, light podzolic horizons are formed or their thick-ness increases [12, 16]. Substantial adverse anthropo-genic changes are observed in soils under reclamationand irrigation (table, 3)

Under recurrent excessive watering, chernozemsand automorphic dark chestnut soils (table, 3.1) with anonpercolative water regime often turn out to be underthe conditions of a secondary stagnant–percolativewater regime. We studied the consequences of thistransformation in a model experiment [5, 8]. Undershort-term (5 h) excessive watering with fresh water, atypical chernozem was shown to quickly degrade. Theshort-term water logging exerts an intense adverseeffect on the mineral and organic fractions of the solidphase of these soils. Calcium, magnesium, iron, alumi-num, and manganese are leached; signs of lessivage arevisible; and low-molecular organic acids, fulvic acids,and amino acids accumulate. As a result of long-termperiodic excessive watering with fresh water, well-expressed acid whitish (podzolized) horizons areformed. This dangerous phenomenon was observed byKhlebnikova on irrigated dark chestnut soils in theVolga River basin [20].

The material presented also shows that the samemechanisms are responsible for the formation of lightacid eluvial horizons in irrigated areas of the steppezone and in drained massifs of the forest one.

The same mechanism—periodic anaerobiosis undera stagnant–percolative regime—is responsible for theextended degradation of soils of rice irrigation systemsin the tropical and subtropical zones (table, 3.2). Here,


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under long-term flooding in the conditions of a stag-nant–percolate water regime and intense infiltrationand decantation of the upper soil horizons, Ca, Mg, Mn,Fe, and Al are actively leached. In the centuries-old cul-ture of rice irrigation in the background of high temper-atures and fast development of anaerobiosis, soils withvery thick secondary podzolic horizons develop. InVietnam, Myanmar, and other countries of southeasternAsia, these degraded soils are referred to as rice pod-zols, which are infertile or weakly fertile eluvial soils.Their use is possible only for cultivation of somelegumes fixing nitrogen from the atmosphere (forinstance, peanuts).

The development of gleying may affect amelioratedsoils not only under a stagnant–percolative but alsounder a stagnant water regime (table, 3.3). If the irriga-tion and ground waters are fresh, lessivage does nottake place, the removal of bi- and trivalent metals isinsignificant, and podzolization is absent. However, inthis case, the soil structure is degraded; the contents ofthe fine earth fractions, the specific surface, and thewater capacity increase; and the water permeability ofthe soils significantly decreases. In the soils, nontroniteand hizingerite accumulate and vertic features appear[5, 8]. Under the stagnant water regime, the fertility ofthe soils (in rice paddies, for example) decreases andtheir physical properties become deteriorated. The res-toration of their fertility first presumes the removal ofexcessive water using gravity and polder drainage sys-tems followed by agromeliorative measures directed atthe acceleration of the surface and soil runoff. In thiscase, deep ameliorative tillage, mole trenching, grassesin the crop rotation, fertilization, and often liming areeffective.

Substantial changes in the water regime result fromthe irrigation of soils in the steppe and semidesert zonesand induced their deep degradation, since the possiblerise of the groundwater table, as a rule, is accompaniedby secondary salinization and solonetzization [6, 15](table, 3.4, 3.5). This problem was widely discussed inthe literature. Efficient technologies for secondarysalinization and solonetzization control were proposed.We shall not consider them in this article, but there arestill some problems that need consideration.

In the arid regions, at close hard groundwater, soilswith surface secondary dolomitized horizons developunder irrigation (table, 3.6). The formation of dense,consolidated horizons decreases the area of plant nutri-tion and drastically decreases the soil fertility. The res-toration of such degraded soils is possible under a dras-tic increase in the partial pressure of carbon dioxide inthe soil air. The following procedures are fulfilled forthis purpose. At first, deep ameliorative tillage is used;then, great doses of organic fertilizers capable of fer-mentation are plowed into the upper soil layers. Afterthese procedures have been accomplished, the wholeameliorated area is flooded for several days in order tocause anaerobic fermentation in the topsoil, to increase

the partial pressure of CO

2

, and to transform weaklysoluble carbonates of Ca and Mg into their easily solu-ble forms (bicarbonates). Then, the excessive water isdischarged to a collector–drainage network. If the sin-gle dissolution of carbonates turns out to be insuffi-cient, the procedure is repeated up to the completeremoval of the dolomite and lime [6].

In Western and Central Asia, heavy-texturedsierozems with a high content of coarse-crystallinegypsum are widespread (table, 3.7). These soils are dis-tinguished by their rather low water permeability; theyare resistant to washing. The Gypsum in these soils notonly lowers the water infiltration and worsens the con-ditions for washing, but also increases the osmotic pres-sure, the availability of water for plants, and negativelyaffects the nitrogen regime of plants. The attempts to usethese soils in irrigation farming remain unsuccessful, andmethods for the optimization of their water regime havenot been elaborated. All this allows recognizing that, pres-ently, the use of these soils in agriculture is not expedientdue to the inefficiency of the expenses related to their ame-lioration and the considerable water amounts required forwashing of the soils [6, 18].

Especially hazardous are situations in irrigated areaswhen the soils on loesses are rich in powdery or finecrystalline gypsum (table, 3, 8).

When such forms of gypsum are abundant, irriga-tion can cause gypsum dissolution and a catastrophicinflow of water to suffusion funnels. As a result, greatlosses of fresh irrigation water may occur on fields andin canals, as well as a rise of the groundwater table, sec-ondary salinization, and water logging of the soils.Measures for the protection of soils against these pro-cesses have been poorly elaborated. It is expedient tocompile maps on the distribution and forms of gypsumand to perform preliminary flooding of canals and fieldsin the areas dangerous in terms of suffusion, pluggingof the funnels found, and arrangement of drains for theprotection of the territory against secondary bogging.

Upon designing the irrigation systems in dry andarid piedmont and mountain regions, soils on pebblealluvium of the river floodplains and terraces should notbe used in irrigation farming in the cases when thethickness of the fine earth layers does not exceed 20 cm(table, 3.9). Plowing of these skeletal soils leads to afast loss of the shallow fertile fine earth horizon. Theirbest use is for the arrangement of rain-fed pastures [7].

In Central Asia and other regions, specific land-scapes—adyrs—are formed by eolian transportation ofcoarse silty particles and their accumulation at the baseof mountain systems. These landscapes adjoin thesouthern slopes of mountain ridges and are character-ized by loess layers many meters thick (table, 3.10). Inthese regions, the groundwater table is deep. The soilsare highly porous and water permeable. Adyrs havebeen used as rain-fed pastures for a long time. In the1950s–1960s, in these areas, irrigation farming wasstarted using systems of surface flooding in ditches and

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furrows. The irrigation water from canals, ditches, andfurrows intensely entered the groundwater causing itsrise and the water saturation of the aeration zones of theadyrs. Since the latter occupy the commanding hypso-metric levels, the saturation of these structures withwater resulted in the formation of powerful mudflowsthat moved down the slopes and destroyed everythingin their path. The first attempt to use soils of adyrs inirrigation farming ended tragically.

Later on, upon developing the adyrs, all the methodsof surface irrigation were abandoned, and wateringusing closed sprinkling and dropping devices came tobe applied. According to this method, gardens and vine-yards are supplied with small amounts of water. At thesame time, the continuous control of the groundwatertable and water regime of the soils should be provided.As the present-day practice showed, under these condi-tions, the soils of adyrs can be efficiently used in irriga-tion farming for a long time.

Land improvement practice

can also cause adversetransformation of the soil water regime and soil degra-dation (table, 4).

We have studied the following dangerous secondaryhydrological situations arising in organic soils andleading to their degradation under land improvement.

The deep ameliorative loosening of nondrainedloamy and clayey gleyic soils (table, 4.1) for the firstyear after its application increases their porosity andpermeability and decreases their density. However, inthe spring flooding of the next year, the improvement ofthe physical properties of the soil turns out to be a rea-son for the great amounts of gravity water in the zoneof loosening (in the layer of 80 cm thick). Under a stag-nant water regime, a huge artificial “hydrological bag”filled with water is formed resulting in the intense gley-ing of the soil profiles from the surface to the bottom ofthe loosened layer. Therefore, after tillage, the aggre-gate state of nondrained hydromorphic soils becomesworse, and amorphous iron hydroxides accumulate.The values of the filtration coefficients decrease by anorder of magnitude, and the total specific surface of thesoil increases, as well as the water-retention capacity.These phenomena occur under conditions of long-termexcessive water within the whole soil profile, whichexcludes the normal growth and development almost allcrops in field rotations. Avoiding such dangerous deg-radation phenomena is possible only if drainage isarranged before the deep loosening [6, 11].

Negative consequences related to the transformationof the hydrological conditions due to ameliorative mea-sures occur not only in mineral but also in peat soils(table, 4.2). The main condition for the stable function-ing of peat soils is their carbon budget (the equilibriumbetween the carbon input and output). Any factor accel-erating the organic matter decomposition in peat soilsmay result in their complete disappearance. This isespecially dangerous in sandy polesie and morainelandscapes and in floodplains where peat layers are

underlain by gleyic sands, marl, and calcareous tuffdeposits. In these cases, different methods of soil sand-ing are used to improve the conditions for agriculture[14, 22]. Sand at rates of 300–600 t/ha is added to theplow layer and mixed with the peat, or sand is distrib-uted over the soil surface. In the latter case, the sand formsa plow horizon 14–16 cm thick (2100–2200 t/ha). As wehave found, the application of sand not only drasticallychanges the hydrothermal regime of drained peat soilsbut also accelerates the organic matter decompositionwithin the whole profile of these soils. It does notinhibit it, as many specialists believe. The rate of thepeat organic matter decomposition under sand additionincreases by 20–50% as compared to the black (usual)system of farming, depending on the method of sandapplication and the weather conditions.

Preventing soil degradation is possible by the cre-ation of bilateral ameliorative systems (drainage–irri-gation), the maintenance of a meadow type of waterregime, using the area as a meadow or increasing theproportion of grasses in the crop rotation, the applica-tion of organic fertilizers, and the plowing of stubbleremains into the soil [14].

Among the agronomic measures (table, 5) that causea drastic transformation of the water regime of soils andtheir degradation is the strong compaction of the layerunder the plow one because of the use of heavy vehicles(table, 5.1). The strong compaction of the soils drasti-cally decreases their porosity, the coefficient of poros-ity, and the volume of the vertical water flow. At thesame time, the surface runoff, erosion instability, andaccumulation of gravity water increase on the lowerparts of slopes, watersheds, and in depressions. Thelong-term water stagnation in these areas causes waterlogging of the soils and negatively affects the growthand development of plants. The results of these pro-cesses are gleying of soils, their podzolization at thebase of slopes, and development of vertic properties insoils of depressions [5].

The restoration of the lost fertility of the soils is pos-sible if one lowers the specific pressure of machines onthe soil surface to 100 kPa or less and substitutes lightervehicles for heavy ones. Among the measures for low-ering the pressure on the soil are the use of twin wheelson heavy machines, decreasing the pressure in tires,and the use of tractors and combines with caterpillarand semicaterpillar tracks. In these cases, mole trench-ing, nondeep loosening (down to 50 cm), and grassrotations are efficient [9, 5].

In reclamation of soils on floodplains with a com-plex relief in ridge–plain, ridge–terrace, and ridgefloodplains, clearing of forests ('urema' forests) and,especially, subsequent plowing of soddy stratifiedsandy soils appear to be a serious hazard (table, 5.2).This is related to the fact that, in the ridge floodplainadjacent to the river bed, the rate of flooding watermovement is maximal. Therefore, the light-texturedsoils of ridge floodplains are exposed to water erosion


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to the greatest extent. Urema forests protect these soilsagainst water erosion. Thus, if a river floodplain is reg-ularly flooded in the spring and autumn, its urema for-ests and sandy soils should be preserved in their naturalstate. This condition is also important, since the localdestruction and erosion of the sandy soils of ridgefloodplains leads to a drastic deterioration of themeadow and plow lands located in the lower reachesbecause of their covering with sand. Not only are thesoils destroyed but also the whole floodplain landscapeis degraded.

The reasons for soil degradation due to road con-struction (table, 6) and industrial production (table, 7)are worth mentioning. In the first case, the adversetransformation of the water regime of soils results fromthe crossing of temporary and permanent stream routesby line constructions (highways, railways, dams, run-ways of airports, etc.). As a result of the cessation of thewater removal after the building of these structures,considerable volumes of gravity water accumulate, andthe soils are waterlogged. Such areas, as a rule, are soonremoved from agricultural use. Similar situations takeplace because of the building of constructions withoutspecial water outlets. In order to avoid the secondarybogging of the soils, free water discharge through out-lets in dams and road embankments should be allowedor pumping of the water to the space outside the damsmust be provided. In the southern regions, this practicemay be complicated by salinization and solonetzizationof soils, and some additional measures concerningdesalinization of the soils will be needed [6, 15].

Industrial production affects the environment and isalso responsible for soil degradation due to changes inthe hydrological conditions. Two kinds of such effectswill be considered. Upon the mining of minerals (forinstance, of brown coal in the Moscow Coal Basin), inthe course of the coal and enclosing rock extraction, thesubsidence of the surface and lowering of hypsometriclevels over vast areas take place (table, 7.1). In thiscase, in the absence of drainage constructions, thegroundwater enters the upper horizons. Secondary soilbogging takes place. This case is poorly investigated,and measures for the protection of the soils have notbeen elaborated. It is worth noting that land fillingand/or depositing of dredged material, designing coul-isse, and the planting of woody and herbaceous plantswith deep root systems, along with some other mea-sures, are useful.

The transformation of the natural hydrologicalregime of soils on limited areas is possible owing totheir flooding by drainage water from mines, opencasts, and other mine works (table, 7.2). In this situa-tion, measures to control the different water flows mayprotect the soils against flooding. A differentiatedapproach should be important for the use of thesewaters while taking into account their chemical compo-sition and physical properties. Drainage water and agri-cultural and municipal waste waters can be used for

irrigating grasses on filter beds, and they can beaccusmulated in storage places and purified.

In regions with complicated relief and in piedmontand mountain areas, changes in the hydrological regimeof soils are often caused by the uncontrolled cutting offorests; the drastic decrease in evapotranspiration; and,as a consequence, water logging of the soils. Landslidesmay be a result of these phenomena. They represent adirect danger for the existence and economic activity ofhumans; this is a reason for the degradation of soils andthe destruction of whole landscapes. Landslides ariseafter long-lasting rains in areas without arborous vege-tation. Under these conditions, a groundwater flow isformed within the unconsolidated deposits on the localconfining layer. When saturated with water, they beginto move and slide down the slope. This process can beretarded or stopped if we use a complex of such mea-sures as the interception of the groundwater flow bytrap canals along the “surface” of sliding, discharge ofperched water from the soil body by material drainage,terracing, construction of concrete or stone supports(aprons) in the lower part of slopes, sowing of perennialgrasses with deep root systems, and planting of treesproviding intense evapotranspiration.

CONCLUSIONS

Degradation phenomena resulting from anthropo-genic effects on the hydrological regime of soils alwaysaccompany human activity in the fields of agriculture,forestry, the water industry, building, and industry. Thetypes of soil degradation are various in their manifesta-tion. As a rule, the degradation processes determine thesoil formation under new secondary conditions. Theseadverse phenomena can be efficiently prevented onlywhen knowledge of their mechanisms is used as thebasis of preventive measures. Therefore, the analysis ofeach degradation phenomenon considered in this articleincluded three items: (1) the causes of the soil degrada-tion, (2) the signs of the degradation phenomena, and(3) the measures recommended for the prevention andelimination of the degradation.

The attempts to generalize and systemize the currentideas of the most unfavorable changes in the waterregime of soils leading to soil degradation haverevealed that the best method of the protection of soilsagainst dangerous changes is the timely application ofpreventive measures. These recommendations are nec-essary for the rational construction of ameliorative sys-tems and agroecological substantiation of agriculture.

Undoubtedly, the information about the degradationprocesses related to the changes in the hydrologicalregime of soils that has been considered in this articleis not comprehensive. Nevertheless, it allows us to rec-ognize the actuality of the problem of soil degradationand the necessity of its further study for efficient use ofmeasures directed at the optimization of soil propertiesand of the soil hydrological regime for environmental,

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agricultural, silvicultural, and hydroeconomic pur-poses.

ACKNOWLEDGMENTSThis work was supported by the Russian Foundation

for Basic Research (project no. 08-04-00139).

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Documents

Degradation of soils as a result of human-induced transformation of their water regime and soil-protective practice