Steppe soils

With respect to soils, a receptor is thus characterized as a specific combination of land use (e g., Forest ecosystem types, agricultural crops) and soil type. The critical loads can be calculated for both agricultural soils (grassland, arable land) with HM inputs with deposition, fertilizers, and wastes, and non-agricultural (forest and steppe) soils, where atmospheric deposition is the only input to the system. 

The water deficiency in Arid ecosystems is the main restricting factor for biogeochem-ical exposure processes. We know that many links of the biogeochemical food web are connected in Steppe soils with invertebrates. Their population varies very much in Steppe ecosystems depending on the moisture conditions (Table 6). For instance, the wet biomass of soil invertebrates in the Meadow Steppe and Forest Steppe ecosystems exceeds that for the Extra-Dry Rocky Desert ecosystems by 150-300 times. 

The content of heavy metals in Steppe soils is tightly connected with their contents in geological rocks. In formation of soil exposure pathways in Desert ecosystems, water-soluble forms of these metals play the most important role. We can see an analogy between the increasing content of elements in soil dead organic matter as a function of decreasing water excess in Forest ecosystems and the increasing content of water-soluble species of chemical elements in the soils of Dry Steppe and Desert ecosystems as a function of enhanced aridity. The accumulation of water-soluble species occurs in the upper horizon for almost all elements, with exception of strontium. The main factor responsible for the accumulation of water-soluble forms is connected with evapotranspiration. 

The belt is mainly represented by Temperate Forest ecosystems on forest-steppe soils (Brown Earth). The analyses of selenium content in various links of the biogeochemical food web (rock, water, soils, grains, hair, etc.) has shown that these... 

Class 5 (the least sensitive) soil include Kashtanozem, Brown soil and Sierozem soil zones in the Plateau of Inner Mongolia and the Loess Plateau, Desert soil zones in He-xi-zou-lang and the Talimu River Basin, Subalpine Steppe soil, Alpine Steppe soil and Alpine Desert soil in the Plateau of Tibet. These kinds of soils, belonging to the soil class of Xerosol or Alpine soil, consist of easy weathering minerals such as carbonate. They show alkaline reactions, with weak leaching and sparse vegetation. Those kinds of soils are insensitive to acid deposition. 

Table 26. Biogeochemical accumulation of silicon. species and carbonate in Meadow Steppe soil profile of Ambiseli plain, Kenya (Kovda, 1984).

Silicon powder in Meadow Steppe soils of Amur river basin 39.3 1.7 0.1... 

In Northeast Asia, the worst sufferers from land degradation are the Kalmykia and Astrakhan regions (6 million ha) in Russia as well as south Siberian steppe soils. In the Siberian steppe at least 25% of arable land is subject to erosion. About 12 million ha have been salinized and waterlogged with development of soil alkalization. The latter process also proceeds in the northeast Kazakhstan steppes. 

Amelung, W., Rodionov, A., Urusevskaja, I.S., Haumaier, L. and Zech, W. (2001) Forms of organic phosphorus in zonal steppe soils of Russia assessed by P NMR. Geoderma 103, 335-350. 

Palygorskites were found by Muir [1951] in the brown and red steppe soils of Syria, as well as in the salt-rich soils formed over limestone in their neighborhood. 

Plate 3 shows a map of dominant soil orders for the entire world. Although this map necessarily lacks detail due to its scale, the relationship between soils and the biosphere is evident. Different terrestrial ecosystems are correlated with climatic conditions and different soils are correlated with both. For example, Mollisols are common in areas where there are prairies or steppes a result of grasses as the dominant vegetation and low, seasonal rainfall. Spodosols occur where coniferous forests dominate and the climate is cold and wet. Comparing Fig. 8-5 and Plate 3 carefully will show how strong this correlation is for the entire Earth. 

Figure 1.1. (a) Climate categories based on mean annual precipitation (b) Desert and steppe boundaries as a function of both mean annual precipitation and temperature according to the Koeppen system arrows show how boundaries shift according to whether precipitation falls mainly in in the summer or winter (after Monger et al., 2004. Reprinted from Encyclopedia of Soils in the Environment, D. Hillel, Tropical soils Arid and Semi-arid, p 183, Copyright (2004), with permission from Elsevier)... 

Thus, the Martonne aridity index defines not only climatic parameters but also vegetational ones. Seasonality of precipitation is another climatic factor that affects desert and steppe boundaries. For a given mean annual temperature, the boundary of a steppe will extend into wetter climates if its precipitation falls mainly in the summer. This is because summer evapotranspiration depletes soil moisture more thoroughly than winter evapotranspiration. For similar reasons, the size of a desert will be larger if its precipitation falls in the summer rather than in the winter (Monger et al., 2004). 

The vast loess and till plains are now colonized by grasses and/or forest. They are the home of some of the best soils of the world the black earths . Deep, black Chernozems occupy the central parts of the Eurasian and North American steppe zones. Brown Kastanozems are typical of the drier parts of the steppe zone and border on arid and semi-arid lands. Dusky red Phaeozems occur in slightly more humid areas such as the American prairies and pampas. 

In chernozems formed on serpentinite diluvium, Co content is in the range of 10-30 mg/kg, while in chestnut and chestnut vertic soils, Co concentrations vary from 3-15 and 15-45 mg/kg, respectively. Soils on basalt, andesite and gabbro contain 15-68 mg/kg total Cu. Total Mn in chernozems is in the range of 520-850 mg/kg. Chestnut soils have 42-106 mg/kg Zn content. Total Zn in saline alkali soils is in the range of 40-60 mg/kg Zn. Bioavailable Zn (ammonium acetate-extractable Zn) in chernozems, chestnut soils and saline alkali soils of the steppe zones varies from trace amounts to 3.8 mg/kg (1-8.3% of total Zn). In chernozems of Northern Bulgaria, total B is in the range of 25-53 mg/kg. Boron increases in saline soils and saline alkali soils. 

Phyletic links of apparent endemic species of the central Ebro valley with easternmost species were revealed after studying the insect communities at the Monegros region. These have a pre-Pleistocene origin of their relict distributions, associated with the persistence of steppe habitats over gypsiferous soils in the area since the Late Tertiary. Distributions of phytophages and their parasitoids on plants such as Krascheninnikovia ceratoides or Juniperus thurifera supported the continuity of their presence in the central Ebro valley through the Quaternary [14]. 

The receptors of interest are soils of agricultural (arable lands, grasslands) and non-agricultural (forests, steppes, heath lands, savanna, etc.) ecosystems. In non-agricultural ecosystems, the atmospheric deposition is the only input of heavy metals. Regarding the Forest ecosystems, a distinction should at least be made between Coniferous and Deciduous Forest ecosystems. When detailed information on the areal distribution of various tree species (e.g., pine, fir, spruce, oak, beech and birch) is available, this should be used since tree species influence the deposition and uptake of heavy metals and the precipitation excess. On a world scale, soil types can be best distinguished on the basis of the FAO-UNESCO Soil Map of the World, climate and ecosystem data from NASA database (1989). 

This sub-region is in the central and east part of the Chuvash administrative region. Most of the sub-region is occupied by Steppe ecosystems with some small spots of Broad-Leafed Forest ecosystems. The predominant soils are Phaerozems. The biogeochemical food web of this sub-region is presented in Figure 3. 

These properties of soils in Steppe ecosystems are favorable to the formation of uppermost humus barrier, where the accumulation of almost all the chemical species occur. The concentration of chemical elements is slightly decreasing downward in soil profile, in parallel with decreasing soil humus content (Figure 2). 

The significant part of heavy metals in the soils of Steppe ecosystems are bound with highly dispersed mineral-organic particles, to a lesser degree, with only organic matter. We can see that the water-soluble and exchangeable forms are less than 1 % of the total content. Specific forms of heavy metals are bound with carbonate and gypsum in B and C horizons (Table 5). 

Role of Humidity in Soil Exposure Pathway Formation in Steppe and Desert Ecosystems... 

Table 5. Distribution of Co in Calcaric Chernozem and Chestnut soil of Meadow Steppe ecosystem in the south part of East European Plain.

The humus content in Steppe ecosystem soils reflects the total biomass production and humidity. 

Incubation of diuron in soils releases carbon dioxide (Madhun and Freed, 1987). The rate of carbon dioxide formation nearly tripled when the soil temperature was increased from 25 to 35 °C. Reported half-lives in an Adkins loamy sand are 705, 414, and 225 d at 25, 30, and 35 °C, respectively. However, in a Semiahoo mucky peat, the half-lives were considerable higher 3,991, 2,164, and 1,165 d at 25, 30, and 35 °C, respectively (Madhun and Freed, 1987). Under aerobic conditions, biologically active, organic-rich, diuron-treated pond sediment (40 pg/mL) converted diuron exclusively to CPDU (Attaway et al., 1982, 1982a Stepp et al., 1985). At 25 and 30 °C, 90% degradation was observed after 55 and 17 d, respectively (Attaway, 1982a). 

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