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The geological cycle (large circulation of substances in nature) is the cycle of substances, the driving force of which is exogenous and endogenous geological processes.
Geological circulation - the circulation of substances, the driving force of which is exogenous and endogenous geological processes.
The boundaries of the geological cycle are much wider than the boundaries of the biosphere, its amplitude captures the layers of the earth's crust far beyond the biosphere. And, most importantly, living organisms play a secondary role in the processes of this cycle.
In this way, geological cycle substances proceeds without the participation of living organisms and redistributes matter between the biosphere and the deeper layers of the Earth.
The most important role in the large cycle of the geological cycle is played by small cycles of matter, both biospheric and technospheric, once in which the substance is switched off for a long time from the large geochemical flow, transforming in endless cycles of synthesis and decomposition.
The most important role in the large cycle of geological circulation is played by small cycles of matter, both biospheric and technospheric, once in which, the substance is switched off for a long time from the large geochemical flow, transforming in endless cycles of synthesis and decomposition.
This carbon takes part in the slow geological cycle.
It is this carbon that takes part in the slow geological cycle. Life on Earth and the gaseous balance of the atmosphere are supported by the relatively small amounts of carbon contained in plant (5 10 t) and animal (5 109 t) tissues participating in the small (biogenic) cycle. However, at present, a person is intensively closing the cycle of substances, including carbon. For example, it is estimated that the total biomass of all domestic animals already exceeds the biomass of all wild land animals. The areas of cultivated plants are approaching the areas of natural biogeocenoses, and many cultural ecosystems in terms of their productivity, continuously increased by man, are significantly superior to natural ones.
The most extensive in time and space is the so-called geological cycle of matter.
There are 2 types of circulation of substances in nature: a large or geological cycle of substances between land and ocean; small or biological - between soil and plants.
The water extracted by the plant from the soil in the vapor state enters the atmosphere, then, cooling, condenses and again returns to the soil or ocean as precipitation. The geological water cycle provides mechanical redistribution, sedimentation, accumulation of solid sediments on land and at the bottom of water bodies, as well as in the process of mechanical destruction of soils and rocks. However chemical function water is carried out with the participation of living organisms or their metabolic products. Natural waters, like soils, are a complex bio-inert substance.
The geochemical activity of man is becoming comparable in scale with biological and geological processes. In the geological cycle, the link of denudation sharply increases.
The factor that leaves the main imprint on general character and biological. At the same time, the geological water cycle is constantly striving to wash all these elements out of the strata of dry land into the ocean basin. Therefore, the preservation of plant food elements within the land requires their conversion to an absolutely water-insoluble form. This requirement is met by a living organic.
All substances on the planet are in the process of circulation. Solar energy causes two cycles of matter on Earth: large (geological, biospheric) and small (biological).
The large circulation of substances in the biosphere is characterized by two important points: it is carried out throughout the entire geological development Earth and is a modern planetary process that takes a leading part in further development biosphere.
The geological cycle is associated with the formation and destruction of rocks and the subsequent movement of destruction products - detrital material and chemical elements. A significant role in these processes was played and continues to be played by the thermal properties of the surface of land and water: absorption and reflection sun rays, thermal conductivity and heat capacity. Unstable hydrothermal regime of the Earth's surface, together with planetary system Atmospheric circulation determined the geological circulation of substances, which at the initial stage of the Earth's development, along with endogenous processes, was associated with the formation of continents, oceans and modern geospheres. With the formation of the biosphere, the products of vital activity of organisms were included in the great cycle. The geological cycle supplies living organisms with nutrients and largely determines the conditions for their existence.
Main chemical elements lithospheres: oxygen, silicon, aluminum, iron, magnesium, sodium, potassium and others - participate in a large circulation, passing from the deep parts of the upper mantle to the surface of the lithosphere. Igneous rock formed during crystallization
Magma, having entered the surface of the lithosphere from the depths of the Earth, undergoes decomposition and weathering in the biosphere. Weathering products pass into a mobile state, are carried by waters and wind to low relief places, fall into rivers, the ocean and form thick strata of sedimentary rocks, which, over time, sinking to depth in areas with elevated temperature and pressure, undergo metamorphosis, i.e., "remelt". During this remelting, a new metamorphic rock appears, entering the upper horizons of the earth's crust and re-entering the circulation of substances. (Fig. 32).
Rice. 32. Geological (large) circulation of substances
Easily mobile substances - gases and natural waters that make up the planet's atmosphere and hydrosphere. The material of the lithosphere cycles much more slowly. In general, each circulation of any chemical element is part of the general large circulation of substances on Earth, and all of them are closely interconnected. Living matter The biosphere in this cycle does a great job of redistributing chemical elements that are constantly circulating in the biosphere, passing from the external environment into organisms and again into the external environment.
Small, or biological, circulation of substances- this is
circulation of substances between plants, animals, fungi, microorganisms and soil. The essence of the biological cycle is the flow of two opposite, but interrelated processes - the creation of organic substances and their destruction. The initial stage in the emergence of organic substances is due to the photosynthesis of green plants, i.e., the formation of living matter from carbon dioxide, water, and simple mineral compounds using solar energy. Plants (producers) extract molecules of sulfur, phosphorus, calcium, potassium, magnesium, manganese, silicon, aluminum, zinc, copper and other elements from the soil in a solution. Herbivorous animals (consumers of the first order) absorb compounds of these elements already in the form of food plant origin. Predators (consumers of the second order) feed on herbivorous animals, consuming more than complex composition, including proteins, fats, amino acids and other substances. In the process of destruction by microorganisms (decomposers) of organic substances of dead plants and animal remains, simple mineral compounds enter the soil and aquatic environment, available for assimilation by plants, and the next round of the biological cycle begins. (Fig. 33).
To endogenous processes include: magmatism, metamorphism (the action of high temperatures and pressure), volcanism, the movement of the earth's crust (earthquakes, mountain building).
To exogenous- weathering, the activity of atmospheric and surface waters of the seas, oceans, animals, plant organisms and especially man - technogenesis.
Interaction of internal and external processes forms great geological cycle of matter.
During endogenous processes, mountain systems, uplands, oceanic depressions are formed, during exogenous processes, igneous rocks are destroyed, the products of destruction move into rivers, seas, oceans and sedimentary rocks form. As a result of the movement of the earth's crust, sedimentary rocks sink into deep layers, undergo metamorphism processes (the action of high temperatures and pressure), and metamorphic rocks are formed. In deeper layers, they turn into molten ...
state (magmatization). Then, as a result of volcanic processes, they enter the upper layers of the lithosphere, on its surface in the form of igneous rocks. This is how soil-forming rocks are formed and various forms relief.
Rocks, from which the soil is formed, are called soil-forming or parent. According to the formation conditions, they are divided into three groups: igneous, metamorphic and sedimentary.
Igneous rocks consist of compounds of silicon, Al, Fe, Mg, Ca, K, Na. Depending on the ratio of these compounds, acidic and basic rocks are distinguished.
Acid (granites, liparites, pegmatites) have a high content of silica (more than 63%), potassium and sodium oxides (7-8%), calcium and Mg oxides (2-3%). They are light and brown in color. The soils formed from such rocks have a loose structure, high acidity and are infertile.
The main igneous rocks (basalts, dunites, periodites) are characterized by a low content of SiO 2 (40-60%), an increased content of CaO and MgO (up to 20%), iron oxides (10-20%), Na 2 O and K 2 O less less than 30%.
The soils formed on the weathering products of the main rocks have an alkaline and neutral reaction, a lot of humus and high fertility.
Igneous rocks make up 95% of the total mass of rocks, but as soil-forming rocks they occupy small areas (in the mountains).
metamorphic rocks, are formed as a result of recrystallization of igneous and sedimentary rocks. These are marble, gneiss, quartz. Occupy a small specific gravity as soil-forming rocks.
Sedimentary rocks. Their formation is due to the processes of weathering of igneous and metamorphic rocks, the transfer of weathering products by water, glacial and air flows and deposition on the land surface, on the bottom of oceans, seas, lakes, in floodplains of rivers.
According to their composition, sedimentary rocks are subdivided into clastic, chemogenic and biogenic.
clastic deposits differ in the size of debris and particles: these are boulders, stones, gravel, crushed stone, sands, loams and clays.
Chemogenic deposits formed as a result of precipitation of salts from aqueous solutions in sea bays, lakes in hot climates or as a result of chemical reactions.
These include halides (rock and potassium salt), sulfates (gypsum, anhydride), carbonates (limestone, marl, dolomites), silicates, phosphates. Many of them are raw materials for the production of cement, chemical fertilizers, and are used as agricultural ores.
Biogenic deposits formed from accumulations of remains of plants and animals. These are: carbonate (biogenic limestones and chalk), siliceous (dolomite) and carbonaceous rocks (coals, peat, sapropel, oil, gas).
The main genetic types of sedimentary rocks are:
1. Eluvial deposits- weathering products of rocks remaining on the sheet of their formation. The eluvium is located at the tops of the watersheds, where the washout is weakly expressed.
2. deluvial deposits- erosion products deposited by temporary streams of rain and melt water in the lower part of the slopes.
3. proluvial deposits- formed as a result of the transfer and deposition of weathering products by temporary mountain rivers and floods at the foot of the slopes.
4. Alluvial deposits- are formed as a result of the deposition of weathering products by river waters entering them with surface runoff.
5. Lacustrine deposits– bottom sediments of lakes. Silts with a high content of organic matter (15-20%) are called sapropels.
6. marine sediments- bottom sediments of the seas. During the retreat (transgression) of the seas, they remain as soil-forming rocks.
7. Glacial (glacial) or moraine deposits- products of weathering of various rocks, displaced and deposited by the glacier. This is an unsorted coarse-grained red-brown or gray material with inclusions of stones, boulders, and pebbles.
8. Fluvioglacial (water-glacial) deposits temporary streams and closed reservoirs formed during the melting of the glacier.
9. Cover clays belong to extra-glacial deposits and are considered as deposits of shallow-water near-glacial floods of melt water. They overlap the madder from above with a layer of 3-5 m. They are yellow-brown in color, well sorted, do not contain stones and boulders. Soils on cover loams are more fertile than on madder.
10. Loesses and loess-like loams are characterized by pale yellow color, high content of silt and silty fractions, loose structure, high porosity, high content of calcium carbonates. Fertile gray forest, chestnut soils, chernozems and gray soils were formed on them.
11. Aeolian deposits formed as a result of the action of the wind. The destructive activity of the wind is composed of corrosion (honing, sanding of rocks) and deflation (blowing and transport by wind small particles soils). Both of these processes taken together constitute wind erosion.
Basic schemes, formulas, etc. illustrating the content: presentation with photographs of weathering types.
Questions for self-control:
1. What is weathering?
2. What is magmatization?
3. What is the difference between physical and chemical weathering?
4. What is the geological cycle of matter?
5. Describe the structure of the Earth?
6. What is magma?
7. What layers does the core of the Earth consist of?
8. What are breeds?
9. How are breeds classified?
10. What is loess?
11. What is a faction?
12. What characteristics are called organoleptic?
Main:
1. Dobrovolsky V.V. Geography of Soils with Fundamentals of Soil Science: Textbook for High Schools. - M .: Humanit. ed. Center VLADOS, 1999.-384 p.
2. Soil science / Ed. I.S. Kaurichev. M. Agropromiadat ed. 4. 1989.
3. Soil science / Ed. V.A. Kovdy, B.G. Rozanov in 2 parts M. Higher School 1988.
4. Glazovskaya M.A., Gennadiev A.I. Geography of Soils with Fundamentals of Soil Science, Moscow State University. 1995
5. Rode A.A., Smirnov V.N. Soil science. M. Higher School, 1972
Additional:
1. Glazovskaya M.A. General soil science and soil geography. M. High School 1981
2. Kovda V.A. Fundamentals of the doctrine of soils. M. Science. 1973
3. Liverovsky A.S. Soils of the USSR. M. Thought 1974
4. Rozanov B. G. ground cover the globe. M. ed. W. 1977
5. Aleksandrova L.N., Naydenova O.A. Laboratory and practical classes in soil science. L. Agropromizdat. 1985
Biological (small) cycle - the circulation of substances between plants, wildlife, microorganisms and soil. Its basis is photosynthesis, i.e., the conversion of the radiant energy of the Sun into energy by green plants and special microorganisms chemical bonds organic substances. Photosynthesis caused the appearance of oxygen on Earth with the help of green organisms, the ozone layer and the conditions for biological evolution.[ ...]
The small biological cycle of substances is of particular importance in soil formation, since it is the interaction of biological and geological cycles that underlies the soil-forming process.[ ...]
The nitrogen cycle is currently exposed strong impact from the side of man. On the one hand, the mass production of nitrogen fertilizers and their use lead to excessive accumulation of nitrates. Nitrogen supplied to the fields in the form of fertilizers is lost due to crop alienation, leaching and denitrification. On the other hand, when the rate of conversion of ammonia to nitrates decreases, ammonium fertilizers accumulate in the soil. It is possible to suppress the activity of microorganisms as a result of soil contamination with industrial waste. However, all these processes are rather local in nature. Much more important is the release of nitrogen oxides into the atmosphere when fuel is burned at thermal power plants and in transport. Nitrogen "fixed" in industrial emissions is toxic, unlike biologically fixed nitrogen. natural processes nitrogen oxides appear in the atmosphere in small quantities as intermediate products, but in cities and industrial areas, their concentrations become dangerous. They irritate the respiratory organs, and under the influence of ultraviolet radiation, reactions occur between nitrogen oxides and hydrocarbons with the formation of highly toxic and carcinogenic compounds.[ ...]
Cycles as a form of movement of matter are also inherent in the biostrome, but here they acquire their own characteristics. The horizontal cycle is represented by a triad: birth - reproduction - death (decomposition); vertical - the process of photosynthesis. Both of them, in the formulation of A. I. Perelman (1975), find unity in a small biological cycle: “... chemical elements in the landscape make cycles, during which they repeatedly enter living organisms (“organize themselves”) and leave them ( “mineralized”)”2.[ ...]
The biological (biotic) cycle is a phenomenon of continuous, cyclic, regular, but uneven in time and space, redistribution of matter, energy1 and information within ecological systems various hierarchical levels of organization - from biogeocenosis to the biosphere. The circulation of substances on the scale of the entire biosphere is called a large circle (Fig. 6.2), and within a specific biogeocenosis - a small circle of biotic exchange.[ ...]
Any biological cycle is characterized by the repeated inclusion of atoms of chemical elements in the bodies of living organisms and their release into the environment, from where they are again captured by plants and involved in the cycle. A small biological cycle is characterized by capacity - the number of chemical elements that are simultaneously in the composition of living matter in a given ecosystem, and speed - the amount of living matter formed and decomposed per unit time.[ ...]
The small biological cycle of substances is based on the processes of synthesis and destruction of organic compounds with the participation of living matter. Unlike a large one, a small cycle is characterized by an insignificant amount of energy.[ ...]
On the contrary, the biological circulation of matter takes place within the boundaries of the inhabited biosphere and embodies unique properties living matter of the planet. Being part of a large, small cycle is carried out at the level of biogeocenosis, it lies in the fact that nutrients soils, water, carbon accumulate in the substance of plants, are spent on building the body and life processes of both themselves and organisms - consumers. The decomposition products of organic matter by soil microflora and mesofauna (bacteria, fungi, molluscs, worms, insects, protozoa, etc.) are again decomposed into mineral components, again available to plants and therefore again involved by them in the flow of matter.[ ...]
The described circulation of substances on Earth, supported by solar energy - the circular circulation of substances between plants, microorganisms, animals and other living organisms - is called the biological cycle of substances, or a small cycle. The time of complete metabolism of a substance in a small cycle depends on the mass of this substance and the intensity of the processes of its movement through the cycle and is estimated at several hundred years.[ ...]
There are large and small - (biological) cycles of matter in nature, the water cycle.[ ...]
Despite the relatively small thickness of the water vapor layer in the atmosphere (0.03 m), it is atmospheric moisture that plays the main role in water circulation and its biogeochemical cycle. In general, for the entire globe there is one source of water inflow - precipitation - and one source of flow - evaporation, which is 1030 mm per year. In the life of plants, a huge role of water belongs to the implementation of the processes of photosynthesis (the most important link in the biological cycle) and transpiration. Evapotranspiration, or the mass of water evaporated by woody or herbaceous vegetation, the soil surface, plays an important role in the water cycle on the continents. Groundwater, penetrating through plant tissues in the process of transpiration, brings mineral salts necessary for the life of the plants themselves.[ ...]
On the basis of a large geological cycle, a cycle of organic substances arose - a small one, which is based on the processes of synthesis and destruction of organic compounds. These two processes provide life on Earth. The energy of the biological cycle is only 1% of the captured Earth solar energy, but it is she who does the enormous work of creating living matter.[ ...]
Solar energy provides two cycles of matter on Earth: geological, or large, and small, biological (biotic).[ ...]
The destabilization of the nitrification process disrupts the entry of nitrates into the biological cycle, the amount of which predetermines the response to a change in the habitat in the complex of denitrifiers. Enzyme systems of denitrifiers reduce the rate of complete recovery, less involving nitrous oxide in the final stage, the implementation of which requires significant energy costs. As a result, the content of nitrous oxide in the above ground atmosphere of eroded ecosystems reached 79 - 83% (Kosinova et al., 1993). The alienation of some organic matter from chernozems under the influence of erosion is reflected in the replenishment of the nitrogen fund in the course of photo- and heterotrophic nitrogen fixation: aerobic and anaerobic. Early stages of erosion rapidly it is precisely anaerobic nitrogen fixation that is suppressed due to the parameters of the labile part of organic matter (Khaziev and Bagautdinov, 1987). The activity of invertase and catalase enzymes in highly eroded chernozems decreased by more than 50% compared to non-eroded chernozems. In gray forest soils, as their washout increases, the invertase activity decreases most sharply. If in slightly eroded soils there is a gradual attenuation of activity with depth, then in heavily eroded soils, invertase activity is very low or not detected already in the subsurface layer. The latter is associated with the emergence of illuvial horizons with extremely low enzyme activity on the day surface. According to the activity of phosphatase and, especially, catalase, no clear dependence on the degree of soil erosion was observed (Lichko, 1998).[ ...]
Landscape geochemistry reveals the hidden, most profound side of the small geographical circulation of matter and energy. The concept of a small geographic circulation has not yet been sufficiently developed in physical geography. AT general view it can be represented as a multi-stringed not completely closed circular flow, consisting of incoming and radiated heat, the biological cycle of chemical elements, a small water cycle (precipitation - evaporation, ground and underground runoff and inflow), aeolian migration - bringing in and removal - mineral matter. [...]
The weakening of the sod process of soil formation is due to the low intensity of the biological cycle, low productivity of vegetation. Annual litter with a total biomass of about Yut/ha does not exceed 0.4-0.5 t/ha. The bulk of the litter is represented by root residues. About 70 kg/ha of nitrogen and 300 kg/ha of ash elements are involved in the biological cycle.[ ...]
Tropical rainforests are fairly ancient climax ecosystems in which nutrient cycling has been brought to perfection - they are little lost and immediately enter the biological cycle carried out by mutualistic organisms and shallow, for the most part airy, with powerful mycorrhiza, tree roots. It is thanks to this that forests grow so luxuriantly on scarce soils.[ ...]
The formation of the chemical composition of the soil is carried out under the influence of a large geological and small biological cycle of substances in nature. The most easily removed from the soil are elements such as chlorine, bromine, iodine, sulfur, calcium, magnesium, sodium.[ ...]
Due to the highest activity of biogeochemical processes and the colossal volumes and scales of the circulation of substances, biologically significant chemical elements are in constant cyclic motion. According to some estimates, if we assume that the biosphere has existed for at least 3.5-4 billion years, then all the water of the World Ocean has passed through the biogeochemical cycle at least 300 times, and the free oxygen of the atmosphere - at least 1 million times. The cycle of carbon occurs in 8 years, nitrogen in 110 years, oxygen in 2500 years. The main mass of carbon concentrated in the carbonate deposits of the ocean floor (1.3 x 1016 t), other crystalline rocks (1 x 1016 t), coal and oil (0.34 x 1016 t), participates in a large cycle. Carbon contained in plant (5 x 10 mt) and animal tissues (5 x 109 mt) participates in a small cycle (biogeochemical cycle).[ ...]
However, on land, in addition to the precipitation brought from the ocean, evaporation and precipitation occur along the water cycle, which is closed on land. If the biota of the continents did not exist, then these additional land precipitation would be much less than the precipitation brought from the ocean. Only the formation of vegetation cover and soil leads to a large amount of evaporation from the land surface. With the formation of vegetation cover, water accumulates in the soil, plants and the continental part of the atmosphere, which leads to an increase in the closed circulation on land. At present, precipitation on land is, on average, three times higher than river runoff. Consequently, only one third of precipitation is brought from the ocean and more than two thirds is provided by the closed water cycle on land. Thus, water on land becomes biologically accumulative, main part water regime land is formed by biota and can be regulated biologically.[ ...]
It is convenient to identify some of the main features of the manifestation of the first and second forces, based on the idea of the action of matter cycles on Earth: large - geological (geocircle) and small - biological (biocircle from).[ ...]
The plant communities of the southern taiga are more resistant to chemical pollution than those of the northern taiga. The low stability of the northern taiga cenoses is due to their low species diversity and simpler structure, the presence of species sensitive to chemical pollution (mosses and lichens), low productivity and capacity of the biological cycle, and less ability to recover.[ ...]
However, any ecosystem, regardless of size, includes a living part (biocenosis) and its physical, that is, inanimate, environment. At the same time, small ecosystems are part of ever larger ones, up to the global ecosystem of the Earth. Similarly, the general biological cycle of matter on the planet also consists of the interaction of many smaller, private cycles.[ ...]
Soil is an integral component of terrestrial biogeocenoses. It carries out conjugation (interaction) of large geological and small biological cycles of substances. Soil is a unique gGo of the complexity of the material composition natural formation. Soil matter is represented by four physical phases: solid (mineral and organic particles), liquid (soil solution), gaseous (soil air) and living (organisms). Soils are characterized by a complex spatial organization and differentiation of features, properties and processes.[ ...]
According to the first corollary, we can only count on low-waste production. Therefore, the first stage in the development of technologies should be their low resource intensity (both at the input and at the output - economy and insignificant emissions), the second stage will be the creation of a cyclical production (the waste of some can be raw materials for others) and the third - the organization of a reasonable disposal of inevitable residues and neutralization of irremovable energy waste. The notion that the biosphere works on the principle of non-waste is erroneous, since it always accumulates substances leaving the biological cycle that form sedimentary rocks.[ ...]
The essence of soil formation, according to V. R. Williams, is defined as the dialectical interaction of the processes of synthesis and decomposition of organic matter, which occurs in the system of a small biological cycle of substances.[ ...]
On the different stages development of the biosphere, the processes in it were not the same, despite the fact that they followed similar patterns. The presence of a pronounced circulation of substances, according to the law of the global closure of the biogeochemical cycle, is a mandatory property of the biosphere at any stage of its development. Probably, this is an immutable law of its existence. Particular attention should be paid to the increase in the share of the biological, and not the geochemical, component in the closure of the biogeochemical cycle of substances. If at the first stages of evolution the general biospheric cycle prevailed - a large biospheric circle of exchange (at first only within aquatic environment, and then divided into two subcycles - land and ocean), then in the future it began to be crushed. Instead of a relatively homogeneous biota, ecosystems appeared and became more and more deeply differentiated. different levels hierarchy and geographical dislocation. Small, biogeocenotic, exchange circles have gained importance. The so-called "exchange of exchanges" arose - a harmonious system of biogeochemical cycles with the highest value of the biotic component.[ ...]
In mid-latitudes, the income of energy from the Sun is 48-61 thousand GJ/ha per year. With the introduction of additional energy of more than 15 GJ/ha per year, processes unfavorable for the environment occur - soil erosion and deflation, silting and pollution of small rivers, eutrophication of water bodies, and violations of the biological cycle in ecosystems.[ ...]
The East Siberian region is characterized by severe winters with little snow and mainly summer precipitation, which washes the soil layer. As a result, in the East Siberian chernozems, a periodic flushing regime takes place. The biological cycle is suppressed by low temperatures. As a result, the content of humus in the Trans-Baikal chernozems is low (4-9%) and the thickness of the humus horizon is small. The content of carbonates is very low or absent. Therefore, the chernozems of the East Siberian group are called low-carbonate and non-carbonate (for example, leached low-carbonate or non-carbonate chernozems, ordinary low-carbonate chernozems).[ ...]
Most minor elements at concentrations common in many natural ecosystems have little effect on organisms, perhaps because organisms have adapted to them. Thus, the migrations of these elements were of little interest to us, if the environment did not get into the environment too often. by-products mining industry, various industries, chemical industry and modern Agriculture, products containing high concentrations heavy metals, toxic organic compounds and other potentially dangerous substances. Even a very rare element, if it is introduced into the environment in the form of a highly toxic metal compound or a radioactive isotope, can acquire an important biological significance, since even a small (from a geochemical point of view) amount of such a substance can have a pronounced biological effect.[ ...]
The chemical nature of vitamins and other growth-stimulating organic compounds, as well as the need for them in humans and domestic animals, has long been known; however, research on these substances at the ecosystem level has just begun. The content of organic nutrients in water or soil is so low that they should be called "micronutrients" as opposed to "macronutrients" such as nitrogen and "micronutrients" such as "trace" metals (see Chapter 5). Often the only way to measure their content is a biological sample: special strains of microorganisms are used, the growth rate of which is proportional to the concentration of organic nutrients. As emphasized in the previous section, the role of a particular substance and the rate of its flow cannot always be judged by its concentration. It is now becoming clear that organic nutrients play an important role in community metabolism and that they may be a limiting factor. This interesting area research in the near future will undoubtedly attract the attention of scientists. The following description of vitamin B12 (cobalamin) cycling, taken from Provasoli (1963), shows how little we know about organic nutrient cycling.[ ...]
V.R. Williams (1863-1939) developed the doctrine of the factors of agriculture. According to the first law of agriculture, none of the factors of plant life can be replaced by another. And, besides, all the factors of plant life, of course, are equivalent (the second law). Let us single out his important idea that the soil is the result of the interaction of a small - biological and large - geological cycle of matter.[ ...]
V. R. Williams closely connected his positions in the field of genetic soil science and the study of soil fertility with practical matters agriculture and put them in the basis of the grass-field system of agriculture. The most important and original views were expressed by V.R. Williams on the role of living organisms in soil formation, on the essence of the soil-forming process and the nature of individual specific processes, on the small biological cycle of substances, on soil fertility, soil humus and soil structure.[ ...]
These approaches are essentially related as a strategy and tactics, as a choice of long-term behavior and a measure of first-priority decisions. They cannot be separated: pollution human environment environment harms other organisms and wildlife in general, and degradation natural systems weakens their ability to naturally cleanse the environment. But it should always be understood that it is impossible to preserve the quality of the human environment without the participation of natural ecological mechanisms. Even if we master low-polluting technologies, we will not achieve anything if at the same time we do not stop preventing nature from regulating the composition of the environment, purifying it and making it habitable. The cleanest technologies and the most advanced environmental protection devices will not save us if deforestation continues, diversity decreases species disrupt the cycle of substances in nature. It should be emphasized that from an ecological point of view, the concept of “protection” is flawed from the very beginning, since activities should be built in such a way as to prevent all effects and results from which one would have to “protect” later.[ ...]
About 99% of all matter in the biosphere is transformed by living organisms, and the total biomass of the living matter of the Earth is estimated at only 2.4 1012 tons of dry matter, which is 10-9 part of the mass of the Earth. The annual reproduction of biomass is about 170 billion tons of dry matter. The total biomass of plant organisms is 2500 times greater than that of animals, but the species diversity of the zoosphere is 6 times richer than that of the phytosphere. If we lay out all living organisms in one layer, then a biological cover with a thickness of only 5 mm would form on the surface of the Earth. But despite the small size of the biota, it is it that determines the local conditions on the surface of the earth's crust. Its existence is responsible for the appearance of free oxygen in the atmosphere, the formation of soils and the cycle of elements in nature.[ ...]
We have already described mushrooms above, and we actually call its fruiting body a mushroom, but this is only part huge organism. This is an extensive network of microscopic fibers (reefs), which is called mycelium (mycelium) and penetrates detritus, mainly wood, leaf litter, etc. Mycelium, as it grows, releases a significant number of enzymes that decompose wood to a state ready for use, and gradually, the mycelium completely decomposes dead wood. It is interesting, as B. Nebel (1993) writes, that fungi can be found on inorganic soil, since their mycelium is able to extract even very low concentrations of organic substances from its thickness. Bacteria function in a similar way, but at a microscopic level. Very important for maintaining the stability of the biological cycle is the ability of fungi and some bacteria to form huge amounts of spores (reproductive cells). These microscopic particles are carried by air currents in the atmosphere over very considerable distances, which allows them to spread everywhere and give viable offspring in any space in the presence of optimal conditions vital activity.
The biosphere of the Earth is characterized in a certain way by the existing circulation of substances and the flow of energy. The cycle of substances is the repeated participation of substances in the processes that occur in the atmosphere, hydrosphere and lithosphere, including those layers that are part of the Earth's biosphere. The circulation of matter is carried out with the continuous supply of external energy from the Sun and internal energy Earth.
Depending on the driving force, within the circulation of substances, one can distinguish geological (large circulation), biological (biogeochemical, small circulation) and anthropogenic cycles.
Geological cycle (great circulation of substances in the biosphere)
This circulation redistributes matter between the biosphere and deeper horizons of the Earth. driving force this process are exogenous and endogenous geological processes. Endogenous processes occur under the influence of the internal energy of the Earth. This is the energy released as a result radioactive decay, chemical reactions of formation of minerals, etc. Endogenous processes include, for example, tectonic movements, earthquakes. These processes lead to the formation large forms relief (continents, oceanic depressions, mountains and plains). Exogenous processes flow under the influence of the external energy of the Sun. These include the geological activity of the atmosphere, hydrosphere, living organisms and humans. These processes lead to the smoothing of large landforms (river valleys, hills, ravines, etc.).
The geological cycle continues for millions of years and consists in the fact that rocks are destroyed, and weathering products (including water-soluble nutrients) are carried by water flows to the World Ocean, where they form marine strata and only partially return to land with precipitation. Geotectonic changes, the processes of subsidence of the continents and the rise of the seabed, the movement of the seas and oceans for a long time lead to the fact that these strata return to land and the process begins again. The symbol of this circulation of substances is a spiral, not a circle, because. the new cycle of circulation does not exactly repeat the old one, but introduces something new.
To big cycle refers to the water cycle (hydrological cycle) between the land and the ocean through the atmosphere (Fig. 3.2).
The water cycle as a whole plays a major role in shaping natural conditions on our planet. Taking into account the transpiration of water by plants and its absorption in the biogeochemical cycle, the entire supply of water on Earth decays and is restored for 2 million years.
Rice. 3. 2. Water cycle in the biosphere.
In the hydrological cycle, all parts of the hydrosphere are interconnected. More than 500 thousand km3 of water participate in it every year. The driving force behind this process is solar energy. Water molecules under the action of solar energy are heated and rise in the form of gas into the atmosphere (875 km3 of fresh water evaporates daily). As they rise, they gradually cool, condense and form clouds. After sufficient cooling, the clouds release water in the form of various precipitations that fall back into the ocean. Water that has fallen on the ground can follow two different ways: either soak into the soil (infiltration) or run off (surface runoff). On the surface, water flows into streams and rivers that lead to the ocean or other places where evaporation occurs. Water absorbed into the soil can be retained in its upper layers (horizons) and returned to the atmosphere by transpiration. Such water is called capillary. Water that is carried away by gravity and seeps down the pores and cracks is called gravitational water. Gravity water seeps down to an impenetrable layer of rock or dense clay, filling all voids. Such reserves are called groundwater, and their upper bound– level ground water. Underground rock layers through which groundwater flows slowly are called aquifers. Under the influence of gravity, groundwater moves along the aquifer until it finds a “way out” (for example, forming natural springs that feed lakes, rivers, ponds, i.e. become part of surface water). Thus, the water cycle includes three main "loops": surface runoff, evaporation-transpiration, groundwater. More than 500 thousand km3 of water is involved in the water cycle on Earth every year, and it plays a major role in shaping natural conditions.
Biological (biogeochemical) circulation
(small circulation of substances in the biosphere)
The driving force of the biological cycle of substances is the activity of living organisms. It is part of a larger one and takes place within the biosphere at the ecosystem level. A small cycle consists in the fact that nutrients, water and carbon accumulate in the matter of plants (autotrophs), are spent on building bodies and life processes, both plants and other organisms (usually animals - heterotrophs) that eat these plants. The decomposition products of organic matter under the action of destructors and microorganisms (bacteria, fungi, worms) decompose again to mineral components. These inorganic substances can be reused for the synthesis of organic substances by autotrophs.
In biogeochemical cycles, a reserve fund (substances that are not associated with living organisms) and an exchange fund (substances that are connected by direct exchange between organisms and their immediate environment) are distinguished.
Depending on the location of the reserve fund, biogeochemical cycles are divided into two types:
Cycles of the gas type with a reserve fund of substances in the atmosphere and hydrosphere (cycles of carbon, oxygen, nitrogen).
Cycles of sedimentary type with a reserve fund in the earth's crust (circulations of phosphorus, calcium, iron, etc.).
Cycles of the gas type, having a large exchange fund, are more perfect. And besides, they are capable of rapid self-regulation. Sedimentary-type cycles are less perfect, they are more inert, since the bulk of the matter is contained in the reserve fund of the earth's crust in a form inaccessible to living organisms. Such cycles are easily disturbed by various kinds of influences, and part of the exchanged material leaves the cycle. It can return again to the circulation only as a result of geological processes or by extraction by living matter.
The intensity of the biological cycle is determined by temperature environment and the amount of water. For example, the biological cycle proceeds more intensively in wet tropical forests than in the tundra.
Cycles of the main biogenic substances and elements
The carbon cycle
All life on earth is based on carbon. Each molecule of a living organism is built on the basis of a carbon skeleton. Carbon atoms are constantly migrating from one part of the biosphere to another (Fig. 3. 3.).
Rice. 3. 3. Carbon cycle.
The main carbon reserves on Earth are in the form of carbon dioxide (CO2) contained in the atmosphere and dissolved in the oceans. Plants absorb carbon dioxide molecules during photosynthesis. As a result, the carbon atom is converted into a variety of organic compounds and thus included in the structure of plants. Following are several options:
· carbon remains in plants ® plant molecules are eaten by decomposers (organisms that feed on dead organic matter and at the same time break it down to simple inorganic compounds) ® carbon is returned to the atmosphere as CO2;
· plants are eaten by herbivores ® carbon is returned to the atmosphere during the respiration of animals and as they decompose after death; or herbivores will be eaten by carnivores and then the carbon will again return to the atmosphere in the same ways;
Plants die and turn into fossil fuels (e.g. coal) ® carbon is returned to the atmosphere after fuel is used, volcanic eruptions and other geothermal processes.
In the case of the dissolution of the original CO2 molecule in sea water, several options are also possible: carbon dioxide can simply return to the atmosphere (this type of mutual gas exchange between the World Ocean and the atmosphere occurs constantly); carbon can enter the tissues of marine plants or animals, then it will gradually accumulate in the form of sediments on the bottom of the oceans and eventually turn into limestone or again pass from the sediments into sea water.
The CO2 cycle rate is about 300 years.
Human intervention in the carbon cycle (burning of coal, oil, gas, dehumification) leads to an increase in the content of CO2 in the atmosphere and the development of the greenhouse effect. At present, the study of the carbon cycle has become important task for scientists involved in the study of the atmosphere.
Oxygen cycle
Oxygen is the most common element on Earth (sea water contains 85.82% oxygen, atmospheric air 23.15%, and 47.2% in the earth's crust). Oxygen compounds are indispensable for sustaining life (play essential role in the processes of metabolism and respiration, is part of proteins, fats, carbohydrates, of which organisms are “built”). The main mass of oxygen is in bound state(the amount of molecular oxygen in the atmosphere is only 0.01% of general content oxygen in the earth's crust).
Since oxygen is found in many chemical compounds, its circulation in the biosphere is very complex and mainly occurs between the atmosphere and living organisms. The concentration of oxygen in the atmosphere is maintained through photosynthesis, as a result of which green plants, under the influence of sunlight, convert carbon dioxide and water into carbohydrates and oxygen. The bulk of oxygen is produced by land plants - almost ¾, the rest - by photosynthetic organisms of the oceans. A powerful source of oxygen is the photochemical decomposition of water vapor in the upper atmosphere under the influence of the ultraviolet rays of the sun. In addition, oxygen makes the most important cycle, being part of the water. A small amount of oxygen is formed from ozone under the influence of ultraviolet radiation.
The oxygen cycle rate is about 2 thousand years.
Deforestation, soil erosion, various mine workings on the surface reduce total weight photosynthesis and reduce the oxygen cycle over large areas. In addition, 25% of the oxygen generated as a result of assimilation is consumed annually for industrial and domestic needs.
nitrogen cycle
The biogeochemical nitrogen cycle, like the previous cycles, covers all areas of the biosphere (Fig. 3.4).
Rice. 3. 4. Nitrogen cycle.
Nitrogen is included in earth's atmosphere unbound in the form diatomic molecules(approximately 78% of the total volume of the atmosphere is nitrogen). In addition, nitrogen is found in plants and animals in the form of proteins. Plants synthesize proteins by absorbing nitrates from the soil. Nitrates are formed there from atmospheric nitrogen and ammonium compounds present in the soil. The process of converting atmospheric nitrogen into a form usable by plants and animals is called nitrogen fixation. When organic matter rots, a significant part of the nitrogen contained in them turns into ammonia, which, under the influence of nitrifying bacteria living in the soil, is then oxidized into ammonia. nitric acid. This acid, reacting with carbonates in the soil (for example, calcium carbonate CaCO3), forms nitrates. Some of the nitrogen is always released during decay in free form into the atmosphere. In addition, free nitrogen is released during the combustion of organic substances, during the combustion of firewood, coal, and peat. In addition, there are bacteria that, with insufficient air access, can take oxygen from nitrates, destroying them with the release of free nitrogen. The activity of denitrifying bacteria leads to the fact that part of the nitrogen from the form available to green plants (nitrates) becomes inaccessible (free nitrogen). Thus, far from all the nitrogen that was part of the dead plants returns back to the soil (part of it is gradually released in a free form).
The processes that compensate for the loss of nitrogen include, first of all, electrical discharges occurring in the atmosphere, in which a certain amount of nitrogen oxides is always formed (the latter with water give nitric acid, which turns into nitrates in the soil). Another source of replenishment of nitrogen compounds in the soil is the vital activity of the so-called azotobacteria, which are able to assimilate atmospheric nitrogen. Some of these bacteria settle on the roots of plants from the legume family, causing the formation of characteristic swellings - nodules. Nodule bacteria, assimilating atmospheric nitrogen, process it into nitrogen compounds, and plants, in turn, turn the latter into proteins and other compounds. complex substances. Thus, in nature, continuous circulation nitrogen.
Due to the fact that every year with the harvest the most protein-rich parts of plants (for example, grain) are removed from the fields, the soil “requires” to apply fertilizers that compensate for the loss in it. essential elements plant nutrition. The main uses are calcium nitrate (Ca(NO)2), ammonium nitrate (NH4NO3), sodium nitrate (NANO3), and potassium nitrate (KNO3). Also, instead of chemical fertilizers, the plants themselves from the legume family are used. If the amount of artificial nitrogen fertilizers applied to the soil is excessively large, then nitrates also enter the human body, where they can turn into nitrites, which are highly toxic and can cause cancer.
Phosphorus cycle
The bulk of phosphorus is contained in rocks formed in past geological epochs. The content of phosphorus in the earth's crust is from 8 - 10 to 20% (by weight) and it is found here in the form of minerals (fluorapatite, chlorapatite, etc.), which are part of natural phosphates - apatites and phosphorites. Phosphorus can enter the biogeochemical cycle as a result of rock weathering. Erosion processes carry phosphorus into the sea in the form of the mineral apatite. In the transformation of phosphorus big role played by living organisms. Organisms extract phosphorus from soils and water solutions. Further, phosphorus is transferred through the food chains. With the death of organisms, phosphorus returns to the soil and to the silt of the seas, and is concentrated in the form of marine phosphate deposits, which in turn creates conditions for the creation of phosphorus-rich rocks (Fig. 3. 5.).
Rice. 3.5. The cycle of phosphorus in the biosphere (according to P. Duvigno, M. Tang, 1973; with changes).
At misapplication phosphate fertilizers, as a result of water and wind erosion (destruction under the action of water or wind), a large amount of phosphorus is removed from the soil. On the one hand, this leads to excessive consumption of phosphorus fertilizers and depletion of phosphorus-containing ores.
On the other hand, an increased content of phosphorus in waterways its transfer causes a rapid increase in the biomass of aquatic plants, "blooming of reservoirs" and their eutrophication (enrichment with nutrients).
Since plants carry away a significant amount of phosphorus from the soil, and the natural replenishment of soil phosphorus compounds is extremely insignificant, the application of phosphorus fertilizers to the soil is one of the most important measures to increase productivity. Approximately 125 million tons are mined annually in the world. phosphate ore. Most of it is spent on the production of phosphate fertilizers.
Sulfur cycle
The main reserve fund of sulfur is found in sediments, soil and atmosphere. the main role in the involvement of sulfur in the biogeochemical cycle belongs to microorganisms. Some of them are reducing agents, others are oxidizing agents (Fig. 3. 6.).
Rice. 3. 6. Sulfur cycle (according to Yu. Odum, 1975).
In nature, various sulfides of iron, lead, zinc, etc. are known in large quantities. Sulfide sulfur is oxidized in the biosphere to sulfate sulfur. Sulfates are taken up by plants. In living organisms, sulfur is part of amino acids and proteins, and in plants, in addition, it is part of essential oils, etc. The processes of destruction of the remains of organisms in soils and in the silts of the seas are accompanied by complex transformations of sulfur (microorganisms create numerous intermediate sulfur compounds). After the death of living organisms, part of the sulfur is reduced in the soil by microorganisms to H2S, the other part is oxidized to sulfates and is again included in the cycle. Hydrogen sulfide formed in the atmosphere is oxidized and returned to the soil with precipitation. In addition, hydrogen sulfide can re-form "secondary" sulfides, and sulfate sulfur creates gypsum. In turn, sulfides and gypsum are again destroyed, and sulfur resumes its migration.
In addition, sulfur in the form of SO2, SO3, H2S and elemental sulfur is emitted by volcanoes into the atmosphere.
The sulfur cycle can be disrupted by human intervention. The reason for this is the burning of coal and emissions from the chemical industry, resulting in the formation of sulfur dioxide, which disrupts the processes of photosynthesis and leads to the death of vegetation.
Thus, biogeochemical cycles provide homeostasis of the biosphere. However, they are largely subject to human influence. And one of the most powerful anti-environmental actions of a person is associated with the violation and even destruction of natural cycles (they become acyclic).
Anthropogenic cycle
The driving force of the anthropogenic cycle is human activity. This cycle includes two components: biological, associated with the functioning of a person as a living organism, and technical, associated with the economic activities of people. The anthropogenic cycle, unlike the geological and biological cycles, is not closed. This openness causes the depletion of natural resources and pollution of the natural environment.
