Biogeochemical food webs

Biogeochemical provinces are the third order units of biosphere. These are areas whose organisms exhibit permanent characteristic biological reactions to excesses or deficiencies of essential nutrients in the region s biogeochemical food webs. The typical forms of these reactions are endemic diseases. There are two types of biogeochemical provinces ... 

We will consider this scheme in detail. Each system will be described as a combination of biogeochemical food webs and relationships between them. 

Figure 3. General model of bio geo chemical cycles in the Earth s ecosystems. The left part is bio geochemical cycling in terrestrial ecosystems, the right part is aquatic ecosystems and the central part is connected with the atmosphere. The fine solid lines show the biogeochemical food webs (the Latin numbers I-XXI) and directed and reverse relationships between these...

System 242. human nutrition, foodstuffs (XIV) balanced essential trace element daily intake for humans (XVI) human health (XVIII). Research should be carried out on the endemic diseases induced by deficient or excessive content in the biogeochemical food webs of different essential elements, like N, Cu, Se, I, F, Mo, Sr, Zn, etc. 

Field monitoring and experimental simulation allow the researcher to study the variability of different links of biogeochemical food webs and to carry out the biogeochemical mapping of biosphere in accordance with above-mentioned classification regions of biosphere, sub-regions of biosphere and biogeochemical provinces. 

Chemical elements Distribution of sub-regions and biogeochemical provinces Content of elements in biogeochemical food webs Biological reactions of organisms and endemic diseases... 

Mn excess Georgia Excessive content of Mn in all biogeochemical food webs Plant endemic diseases... 

Ni, Mg, Sr excess Co, Mn deficit South Ural Unbalanced ratio of essential elements in all biogeochemical food webs Endemic osteodystrophy in humans and animals... 

Figure 5. A simplified biogeochemical food web in the terrestrial ecosystems.

A simplified biogeochemical food web of heavy metals in the terrestrial ecosystems, including the most important receptors (biogeochemical links) is shown in Figure 5. 

The assessment of a critical limit for the receptor of concern is a second step in the flowchart for calculating critical loads of heavy metals (see Figure 4). Since critical loads of heavy metals are related to the concentration of a single metal in any link of a biogeochemical food web, the correct selection of critical limits is a step of major importance in deriving the critical loads. Those critical limits, which depend on the kind of effects considered and the amount of harm accepted, constitute the basis of the critical load calculation and determine their magnitudes. 

To indicate the transfer of chemicals in a biogeochemical food web, both bioaccumulation factors (BAFs) and bioconcentration factors (BCFs) are used. The following definitions can be applied (de Vries and Bakker, 1998a, 1998b) ... 

This mass balance presents the possible links in the biogeochemical food web for various heavy metals. Some items may be neglected, like degassing of Pb, Cd, Cu and Zn metals. However, this process is of crucial importance for mercury (see Section 3.2). The output of the heavy metals with soil erosion may also be neglected. After elimination of these processes, the simplified following equation is workable. The sum of inputs by deposition, fertilizing, and waste and rubbish as fertilizer stands as the term Critical Load . 

According to the specific characteristics of North Eurasian biogeochemical provinces, the alterations of the biogeochemical food webs were studied for I (endemic goiter), Si (the Urov disease), B (endemic enteritis), Se (endemic myopathia), and Mo (endemic gout). On a basis of these results, the recommendations have been produced for correction of daily intake of essential elements. 

The antagonistic influence on cancer development due to organic carcinogens may be induced by chemical species of Se, As, Al, Co, Cu, Zn and Mo. We should note that the antagonistic effects of the latter metals depend strongly on their concentrations (see above on limit concentrations). Similar interactions are characteristic for the combinations of metals in biogeochemical food webs of various biogeochemical provinces. 

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. 

We can see from Figure 3 that the moderate deficit of I, Co, Zn, Cu, Mo, B, and Mn with optimal ratios of trace metals to I and Si, is characteristic for all links of a biogeochemical food web. These biogeochemical peculiarities favor the optimal physiological regulation of exchange processes in animal and human organisms. However, a moderate deficit of essential trace nutrients weakens the human immune... 

Figure 3. Biogeochemical food web in Pre-Kubnozivilsk sub-region of biosphere.

The deficit of I, Co, Mn, and Zn, moderate excess of Si and disturbed ratios of trace metals to I and Si are characteristic features of the biogeochemical food web of this Pre-Volga sub-region of biosphere. Most of its natural water sources have a decreased content of fluorine. These peculiarities of biogeochemical food web favor the occurrence of tooth decay (caries) and endemic goiter. 

The concentration of nitrogen species in various links of biogeochemical food webs of this province is shown in Table 9. 

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. 

However, in the halo of dispersion of ore deposits many metals (Cu, Mo, Ag, Pg) frequently occur at higher concentrations in the aerial parts (Kovalevsky, 1984). This enlarges greatly the risk of pollutants accumulation in the biogeochemical food webs (Bashkin, 2002). 

Despite the quantitative variability of salts and silicate dust particles in the plants of Arid ecosystems, we can easily discern a trend towards the selective uptake of trace elements. The calculation of coefficient of biogeochemical uptake (Cb) shows the rates of exposure to heavy metals in biogeochemical food webs. One can see that the elements contained in the plant species of both Steppe and Desert ecosystems are in equal measure susceptible to the influence of environmental factors. The most extensively absorbed are Sr, Cu, Mo, and Zn. Their values of Cb are more than unit. The group of other elements, like Ti, Zr, and V, are poorly taken up, with their values of Cb often dropping below 0.1 (see Figures 4 and 5). 

Strontium, barium, manganese, copper, molybdenum, and nickel are elements of strong accumulation in plant species of African Savanna ecosystems, in spite of different content in soils and soil-forming rocks. The Cb values are >1. The other elements, like beryllium, zirconium, titanium and vanadium, are less taken up by plants and their Cb values are less than 0.5. These refer to various exposure pathways to both microbes and plants as links in biogeochemical food webs. 

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