Effect of Deep Freezing on the Morphogenetic Properties of Meadow Podbels in the Middle Reaches of the Amur River

Size: px

Start display at page:

Download "Effect of Deep Freezing on the Morphogenetic Properties of Meadow Podbels in the Middle Reaches of the Amur River"

Angelica Pope
5 years ago
Views:

1 ISSN , Moscow University Soil Science Bulletin, 8, Vol. 63, No. 3, pp Allerton Press, Inc., 8. Original Russian Text A.B. Gyninova, S.A. Shoba, L.D. Balsanova, 8, published in Vestnik Moskovskogo Universiteta. Pochvovedenie, 8, No. 3, pp Effect of Deep Freezing on the Morphogenetic Properties of Meadow Podbels in the Middle Reaches of the Amur River A. B. Gyninova a, S. A. Shoba b, and L. D. Balsanova a a Institute of General and Experimental Biology, Siberian Branch of the Russian Academy of Sciences, ul. M. Sakh yanovoi 6, Ulan-Ude, 6746 Russia b Faculty of Soil Science, Moscow State University, Moscow, Russia Received October 5, 7 Abstract Micromorphological features and physical properties of podbels in the middle reaches of the Amur River have been examined. It is argued that the well-pronounced aggregation in the illuvial horizons of these soils is formed under the impact of cryogenic processes. The bleaching of the eluvial-gley horizons of podbels is also enhanced under the impact of cryogenesis. The corresponding process can be referred to as the cryoeluviation process. DOI: 1.313/S INTRODUCTION Meadow podbels are widespread on vast lacustrine alluvial plains in the middle reaches of the Amur River. They belong to the group of texture-differentiated soils and are characterized by the medium loamy texture in the eluvial part and the heavy loamy or clayey texture in the illuvial part of the profile. A characteristic feature of these soils is the presence of a strongly bleached horizon under the humus horizon within the eluvial part of the profile. According to Ivanov [5], the soil bleaching is caused by the periodical water stagnation and the development of gleyzation in the surface horizons; coloring films are removed from the surface of soil particles, and iron is segregated in the form of abundant nodules. The development of podbels is ensured by a monsoon type of climate with desiccation of the upper soil horizons in the early summer and their overmoistening in the second half of summer. Thus, the pulsating character of redox conditions is typical of these soils and results in the bleaching of the main soil mass and iron segregation in concretions [9, 14]. Some authors argue that the development of meadow podbels is also strongly affected by the deep seasonal freezing with separation of ice lenses [1, 1]. However, there are no works describing the particular effect of cryogenesis on the morphogenetic properties of podbels. MATERIALS AND METHODS To study the role of the cryogenic factor in the development of podbels, three soil trenches of 7 1 m in length were dug on the second terrace of the Amur River in its middle course, not far from the village of Babstovo in the Jewish Autonomous oblast. The trenches crossed different elements of the local microtopography. The soil morphology and, particularly, the network of cryogenic cracks were thoroughly described in the trenches. Thin sections were prepared from undisturbed soil samples taken from the main genetic horizons. The dynamics of soil water in the winter period were studied in auger samples. The relationship between the soil water content and the soil swelling was studied under laboratory conditions. RESULTS The profile of meadow podbels consists of the humus-accumulative horizon (A1), the eluvial-gley horizon (Eg), and illuvial horizons (B1g and B2g); transitional horizons are often distinguished. The humus horizon has a fine granular structure, the eluvial horizon has a thin platy structure, and the illuvial horizon has an angular blocky structure. The physicochemical properties of podbels are specified by the clearly pronounced eluvial illuvial redistribution of the clay fraction with a relative accumulation of silt in the surface horizons. Their reaction is slightly acid and the humus content is high (Table 1). The cation exchange capacity has two maximums in the humus and illuvial horizons. Nonsilicate (dithioniteextractable) iron compounds have an eluvial illuvial distribution, whereas amorphous (oxalate-extractable) iron compounds have a distinct maximum in the surface (eluvial) horizons. A study of the soil morphology showed that soil horizons on elevated elements of the microtopography have a continuous character, as they are rarely disturbed by fissures (Fig. 1a). In the soils of transitional positions, the upper horizons have an intermittent character; numerous fissures forming a polygonal pattern in horizontal cross section dissect them. Loci with an increased content of iron nodules are formed at the 14

EFFECT OF DEEP FREEZING 15 1 1 1 (a) (b) (c) 1 2 3 4 5 6 7 8 9 1 11 12 Fig. 1. Morphology of the profiles of meadow podbels on (a) microelevations and (b) slopes and in (c) microdepressions.

The walls of the fissures are covered by the bleached silty coatings (skeletans) penetrating into the B2g horizon (Fig. 1b).

The maximum thickness of the fissures is in the bleached horizon; it is somewhat lower in the humus horizon. The fissures become narrower and gradually disappear in the illuvial horizons.

2 EFFECT OF DEEP FREEZING (a) (b) (c) Fig. 1. Morphology of the profiles of meadow podbels on (a) microelevations and (b) slopes and in (c) microdepressions. (1) Asod, (2) Al, (3) AlEg, (4) Eg, (5) EgB, (6) Big, (7) B2g, (8) BlB2g, (9) B3g, (1) BC, (11) fissures, and (12) whitish mottles. boundary between the eluvial and illuvial horizons. The walls of the fissures are covered by the bleached silty coatings (skeletans) penetrating into the B2g horizon (Fig. 1b). Within the microlows, the polygonal pattern of fissures is better pronounced, and the surface horizons display features of cryoturbation (Fig. 1c). The maximum thickness of the fissures is in the bleached horizon; it is somewhat lower in the humus horizon. The fissures become narrower and gradually disappear in the illuvial horizons. The effect of cryogenic processes on the soil microfabric can be judged from the character of soil microaggregation and the behavior of soil plasma and soil skeleton [2]. Data on the micromorphological characteristics of studied soil profiles are summarized in Table 2. The soil mass in the humus horizon is well aggregated; the clayey plasma, skeletal particles, and iron concentrations are included in the composition of soil aggregates. In the bleached eluvial-gley horizon, the soil mass has a banded structure with separation of silty and clayey bands. Silty grains are devoid of coloring films. In the illuvial horizons, the soil mass is well aggregated. Both angular blocky aggregates and rounded aggregates with ooidal plasmic fabric are distinguished. Table 1. Physicochemical properties and particle-size distribution in meadow podbels Horizon Depth, ph H2 O Humus, % C ha /C fa Adsorbed bases, Content of particles, %; meq/ g CEC, particle size, mm meq/ g Ca 2+ Mg <.1 A / Eg / B1g B2g BCg

3 16 GYNINOVA et al. Table 2. Micromorphological features of meadow podbels Horizon Components of the soil mass Microfabrics A1 Clayey plasma Aggregated clayey humus Incorporated into the peds Iron concentrations Compact, inside the peds Eg Clayey plasma Concentrated in the lower part of platy peds; scaly microfabric Concentrated in upper part of platy peds; washed off from films Iron concentrations Diffuse in the lower part of platy peds; iron nodules beyond the peds B1g Clayey plasma Ooidsepic plasmic fabric on the surface of rounded peds and striated plasmic fabric on the surface of angular peds; lattisepic plasmic fabric inside the peds Cemented by iron oxides inside the peds; washed off from films on ped faces Iron concentrations Diffuse on the surface and relatively compact inside the peds B2g Clayey plasma Ooidsepic plasmic fabric on the surface of rounded peds; insepic and omnisepic plasmic fabric inside angular peds Inside the peds; washed off from films in bleached loci Iron concentrations Diffuse forms; iron coatings on ped faces BCg Clayey plasma Scaly plasmic fabric in large angular peds Inside angular peds; coloring films are removed from the surface of skeletal particles covering fissure walls Iron concentrations Few diffuse mottles As a rule, the central parts of the aggregates are enriched in iron. In the B2g horizon, the aggregation becomes somewhat weaker, and the mobility of clayey plasma increases; bright ocherous microconcentrations of iron oxides with diffuse boundaries are seen on ped faces. The data on the soil moisture dynamics in the winter period (Fig. 2) attest to a considerable redistribution of moisture in the soil profile. Frequent monsoon rains in the late summer ensure the saturation of clayey soils with water. Despite some decrease in precipitation in the fall, the soil overmoistening is preserved. The soil freezing begins in the late fall and is accompanied by the active migration of water to the freezing front. First, additional portions of water (in the form of ice) are W, % A1Eg Eg A1 EgB B1g X XI XII I II III Months Fig. 2. Changes in the water content of meadow podbels during the winter period. accumulated in the A1 and A1Eg horizons at the expense of water from the Eg horizon; with a lowering of the freezing boundary, additional water accumulates in the Eg and, then, in the EgB horizon. The illuvial horizon B1g is subjected to drying during the winter period. The swelling capacity of meadow podbels (Fig. 3) in the surface horizons is relatively low and reaches 3.2% in the A1 horizon and 1.1% in the Eg horizon. The max- Rv, % Eg B2g B1g A W, % Fig. 3. Swelling of the soil mass of meadow podbels as dependent on the water content.

4 EFFECT OF DEEP FREEZING 17 imum swelling of the soil mass in the A1 horizon is observed upon the water content of 55%; the real water content in this horizon in January is higher and reaches 66%. In the eluvial-gley horizon, the maximum swelling is observed at the water content of 15% (as determined in laboratory experiments); the real water content is four times higher and reaches 67%. The maximum water content in the illuvial horizon is observed at the end of October and generally corresponds to the soil water content at the state of maximum swelling. DISCUSSION The polygonal cracking and cryogenic pedoturbation are characteristic features of freezing soils. The formation of cracks is explained by desiccation of unfrozen soil layers in the course of soil freezing and ice segregation in the upper horizons; the more ice forms in the latter, the more pronounced the soil cracking [4]. Therefore, the polygonal network of cryogenic cracks and fissures is better manifested in the microdepressions of the relief; within the soil profile, this network is most clearly pronounced in the bleached horizon. The reason for the separation of the silty and clayey material in the bleached horizon is the differentiation of the soil mass with respect to the energy of interactions typical of polydispersed systems subjected to freezing [15]. The formation of banded texture is related to the separation of ice schlieren. The upper part of thin platy aggregates is depleted of the clayey and ferruginous plasma; the latter concentrates in the lower part of the aggregates, where the formation of iron concentrations and nodules takes place. The origin of similar fabrics in the pale-podzolic soils of the Russian Plain was described by B.A. Il ichev [6]. The melting of ice schlieren in the spring enhances eluviation processes. Konishchev and Rogov [8] suggested that this process could be referred as the cryoeluviation process. In the studied soils, this process, as well as the eluvial-gley process, leads to the textural differentiation of the soil profile and the formation of the bleached eluvial horizon. It is known that ice segregation upon the freezing of a water-saturated soil is accompanied by the cryogenic destruction of soil aggregates by ice bodies; at the same time, the freezing of a soil with an optimum water content facilitates soil aggregation owing to the compaction of the aggregates by ice bodies forming in large pores. In addition, the cryogenic concentration of soil solution within the unfrozen parts of the soil facilitates the coagulation of soil colloids owing to a higher concentration of electrolytes in the solution [7]. The high degree of aggregation in the illuvial horizons is due to strong shrink swell processes. Upon swelling, the soil volume increases by 5 1% (Fig. 2) due to the high content ( 55%) of labile clay minerals (montmorillonite and mixed-layered phyllosilicates) [11]. Desiccation in the winter is accompanied by the soil shrinking and cracking with the formation of angular blocks. The clayey plasma on the surface of soil aggregates acquires ring-shaped (ooidal) fabric around skeletal particles and iron concentrations in the center. Iron concentration in the central parts of such ooidal aggregates is explained by the dynamics of soil freezing: ice segregation occurs in large pores, whereas the central parts of the aggregates are subjected to desiccation accompanied by the oxidation of iron compounds. The growth and subsequent melting of ice on the surface of the aggregates rearranges the soil plasma into ooidal fabric, and aggregates become somewhat rounded. Similar rounded aggregates have been described in many permafrost-affected and paleocryogenic soils [12, 13]. In the period of summer rains, entrapped air inside the aggregates protects the latter from complete soaking and destruction. However, the clayey plasma on the surface of the aggregates retains its mobility, so that the features of modern clay illuviation are clearly pronounced in the illuvial horizons. CONCLUSIONS Texture-differentiated soils in the middle reaches of the Amur River are known by the name of meadow podbels. These soils develop under conditions of contrasting water and temperature regimes and are subjected to deep freezing in the winter. The soil freezing in the wet state is accompanied by the considerable accumulation of ice schlieren in the eluvial-gley horizon. Ice melting in the spring enhances the process of bleaching of the soil mass. In the illuvial horizons with the high content of swelling clay minerals, the soil freezing facilitates the cryogenic aggregation of the soil mass and the cementation of the aggregates by iron hydroxides. REFERENCES 1. Grishin, I.A., Sokhina, E.N., and Tregubova, V.G., Morphology of Soils and Recent Sediments in the Zeya Region in Relation to Cryogenesis, in Voprosy geografii Dal nego Vostoka (Problems of Geography in the Far East), Khabarovsk, Gugalinskaya, L.A., Pochvoobrazovanie i kriogenez tsentra Russkoi ravniny v pozdnem pleistotsene (Pedogenesis and Cryogenesis on the Central Russian Plain during the Late Pleistocene), Pushchino, Gyninova, A.B. and Shoba, S.A., Micromorphology and Structural State of Drained Meadow Podbels in the Amur Region, in Mikromorfologiya antropogenno izmenennykh pochv (Micromorphology of Anthropogenically Transformed Soils), Moscow, 1988, pp Ershov, E.D., Vlagoperenos i kriogennye tekstury v dispersnykh porodakh (Water Transfer and Cryogenic Textures in Dispersed Rocks), Moscow, Ivanov, G.I., Pochvoobrazovanie na yuge Dal nego Vostoka (Pedogenesis in Southern Regions of the Far East), Moscow, 1976.

5 18 GYNINOVA et al. 6. Il ichev, B.A., Palevo-podzolistye pochvy tsentral noi chasti Russkoi ravniny (Pale-Podzolic Soils of the Central Russian Plain), Moscow, Kachinskii, N.A., Fizika pochvy (Soil Physics), Moscow, Konishchev, V.N. and Rogov, V.V., Micromorphology of Cryogenic Soils and Sediments, Pochvovedenie, 1977, no. 2, pp Kostenkov, N.M., Okislitel no-vosstanovitel nyi rezhim v pochvakh periodicheskogo pereuvlazhneniya (Redox Conditions in Periodically Waterlogged Soils), Moscow, Liverovskii, Yu.A., The Main Geographical and Genetic Features of Soils in the Southern Region of the Far East, in Genezis burykh lesnykh pochv (Genesis of Brown Forest Soils), Vladivostok, 1972, pp Matyushkina, L.A. and Chizhikova, N.P., Chemicomineralogical Features of Fine Fractions in Soils of the Central Amur Lowland, in Ratsional noe ispol zovanie pochv Priamur ya (Rational Use of Soils in the Amur Region), Vladivostok, 1983, pp Morozova, T.D., Permafrost-Affected Pale Soils of Central Yakutia, in Mikromorfologicheskii metod v issledovanii genezisa pochv (Micromorphological Method in the Study of Soil Genesis), Moscow, 1966, pp Sokolov, I.A. and Shoba, S.A., Effect of Freezing and Thawing on Soil Properties in the Zones of Recreational Loads, Biol. Nauki, 1982, no. 7, pp Roslikova, V.I., Margantsevo-zhelezistye novoobrazovaniya v pochvakh ravninnykh landshaftov gumidnoi zony (Manganese Iron Neoformations in Soils of Humid Plain Landscapes), Vladivostok, Tyutyunov, N.A., Protsessy izmeneniya i preobrazovaniya pochv i gornykh porod pri otritsatel nykh temperaturakh (Changes and Transformations of Soils and Hard Rocks at Negative Temperatures), Moscow, 19.

Introduction to Soil Science and Wetlands Kids at Wilderness Camp

Introduction to Soil Science and Wetlands Kids at Wilderness Camp Presented by: Mr. Brian Oram, PG, PASEO B.F. Environmental Consultants http://www.bfenvironmental.com and Keystone Clean Water Team http://www.pacleanwater.org