Biogeochemical Provinces

areas on the surface of the earth which differ in terms of the content (in their soils, waters, and so on) of chemical elements or compounds to which specific biological reactions by the local fauna and flora are related. The composition of the soils affects the selection and distribution of plants as well as their variability under the influence of the various chemical compounds or chemical elements found in the soils. The boundaries for the distribution of a certain flora or fauna within one soil zone often coincide with the area where certain rocks or geological formations have developed. The specific vegetation found on serpentinites and limestones, in undrained saline areas, on sands, and so on is well known. Within a given biogeochemical province, a pronounced shortage or excess in the content of any chemical element in the environment causes biogeochemical endemias, or diseases of plants, animals, and man. For example, in cases of a shortage of iodine in food, man and animals may develop goiters; and in cases of an excess of selenium in the soil, there is the appearance of poisonous selenium flora and many other endemias.

In terms of their genesis, two types of biogeochemical province are distinguished. The first comprises the biogeochemical provinces confined to certain soil zones in the form of individual spots or areas and determined by the insufficiency of one or another chemical element in the environment. For example, the zones of podzolic and soddypodzolic soils in the northern hemisphere stretching across virtually all of Eurasia are characterized by biogeochemical provinces that are related to an insufficiency of iodine, calcium, cobalt, copper, and other elements. Similar biogeochemical provinces and the endemias characteristic for them (goiter, acobaltosis, brittleness of bones in animals, and such) are not encountered in the adjacent zone of chernozems. The reason lies in the great mobility of the ions of I, Ca, Co, Cu, and others, which are easily washed out of the podzolic soils. A similar process occurs in the analogous soils of the southern hemisphere. This type of biogeochemical province has a negative character, since it arises as a result of the insufficiency of one or another chemical element in the environment. The second type is the biogeochemical provinces and endemias encountered in any zone. In this sense they have an intrazonal character and arise on the background of primary or secondary dispersion halos from the substance of ore deposits, salt deposits, volcanic emanations, and so forth. For example, boric biogeochemical provinces and endemias among flora and fauna are detected in undrained areas. Fluorosis in man and animals is encountered in an area of recently active volcanoes and of fluorite and fluorapatite deposits; molybdenosis of animals is encountered within the limits of molybdenum deposits, and so forth. This type of province and endemia has a predominantly positive character, since it is related to the surplus content of the chemical elements in the environment.

The chemical elements which form readily soluble compounds under soil conditions cause the strongest biological reaction in the local flora. The form of occurrence of the chemical elements in the environment is also significant. For example, in animals molybdenum causes a disease only in regions with alkaline soils (molybdic acid produces soluble compounds with alkalis); in regions of acidic soils, excess molybdenum does not cause diseases. The chemical elements Ti, Zr, Hf, Th, Sn, Pt, and many others which under soil conditions do not form easily mobile soluble compounds do not cause the formation of biogeochemical provinces and endemias.

Within the limits of a biogeochemical province, two types of concentration of the chemical elements by the organisms are distinguished: group concentration, in which all types of plants in the given province to one degree or another accumulate a certain chemical element; and selective concentration, in which there are certain concentrator organisms for one or another chemical element regardless of the level of this element’s content in the environment. Various species of plants are known which concentrate certain elements in the biogeochemical provinces and in doing so are subject to variability. This includes the specific calamine flora (which concentrates Zn), the limestone, selenium, halophyte, and serpentinite flora, and many others.

Depending upon the constitutional properties of the given type of organism, and particularly in cases of its protracted isolated existence in one or another biogeochemical province, variability of the organism arises—that is, the appearance of physiological races (without visible external changes), morphs, variations, subspecies, and species. This is accompanied by an increase in the content of the corresponding chemical elements such as Cu, Zn, Se, and Sr in the organisms. Chemical mutants also appear with a change in the number of chromosomes in the cell nuclei and such; the variability can acquire a hereditary character, particularly in microbes.

Many rare and trace chemical elements (microelements) play a significant physiological role, entering into physiologically important organic compounds in the organisms such as respiratory pigments, enzymes, vitamins, hormones, and other accessory, physiologically important substances.

More than 30 chemical elements (Li, B, Be, C, N, F, Na, Mg, Al, Si, P, S, Cl, K, Ca, V, Mn, Cu, Zn, As, Se, Br, Mo, I, Ba, Pb, U, and others) are known which are related to the formation of biogeochemical provinces and endemias and the appearance of concentrator organisms.

On the basis of study of the chemical ecology of a biogeochemical province, the use of chemical elements (B, Cu, Mn, Co, I, and others) as fertilizers or feed supplements for animals has become widespread in combating the corresponding endemias in the biogeochemical province. On the basis of study of the content of the chemical elements in the soils and plants, a biogeochemical method was developed for finding minerals. In the geological past, the biogeochemical provinces also played a significant role in the selection and choice of flora and fauna. The reconstruction of the paleobiogeochemical provinces can explain a great deal in the evolution of the organic world.