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The water cycle. Global carbon and water cycles

The role of water in the processes occurring in the biosphere is enormous. Without water, metabolism in living organisms is impossible. With the advent of life on Earth, the water cycle became relatively complex, since the simple phenomenon of physiological evaporation was supplemented by the more complex process of biological evaporation (transpiration), associated with the life of plants and animals.

Briefly, the water cycle in nature can be described as follows. Water reaches the Earth's surface in the form of precipitation, which is formed mainly from water vapor entering the atmosphere as a result of physical evaporation and evaporation of water by plants. One part of this water evaporates directly from the surface of water bodies or indirectly through plants and animals, while the other feeds groundwater.

The nature of evaporation depends on many factors. Thus, significantly more water evaporates from a unit area in a forest area than from the surface of a water body. With a decrease in vegetation cover, transpiration also decreases, and, consequently, the amount of precipitation.

The flow of water in the hydrological cycle is determined by evaporation, not precipitation. The atmosphere's ability to hold water vapor is limited. An increase in evaporation rates leads to a corresponding increase in precipitation. The water contained in the air in the form of vapor at any moment corresponds to an average layer 2.5 cm thick, evenly distributed over the surface of the Earth. The amount of precipitation that falls per year averages 65 cm. Consequently, water vapor from the atmospheric front circulates approximately 25 times annually (once every two weeks).

The water content in water bodies and soil is hundreds of times greater than in the atmosphere, but it flows through the first two funds at the same speed. The average time of transport of water in its liquid phase across the Earth's surface is about 3650 years, 10,000 times longer than the time of its transport in the atmosphere. Humans in the process of economic activity have a strong impact on the basis of the hydrological cycle - water evaporation.

Pollution of water bodies and, first of all, seas and oceans with petroleum products sharply worsens the process of physical evaporation, and a decrease in forest area - transpiration. This cannot but affect the nature of the water cycle in nature.

Global cycles of vitally important nutrients break up in the biosphere into many small cycles confined to the local habitats of various biological communities. They can be more or less complex and varying degrees of sensitivity of various kinds external influences. But nature has decreed that under natural conditions these biochemical cycles are “exemplary waste-free technologies.” Cyclicity covers 98-99% of nutrients and only 1-2% goes not even to waste, but to the geological reserve.

In contrast to simple transfer - the movement of mineral elements in the large cycle - in the small cycle the most important points are the synthesis and destruction of organic compounds. These two processes underlying life are in a certain relationship, which constitutes one of its main features.

The unique properties of living matter and its biogeochemical functions, manifested in the ability to transform gases and concentrate chemical elements, explain its ability to perform geochemical work on the planet that is grandiose in scale and consequences.

As noted above, the basis for the functioning of the natural system (NS) are energy and material connections. The substance in the PS moves in a vicious circle, forming a biogeochemical cycle .

On the way from autotrophs to heterotrophs, nutrients can enter the so-called reserve funds, kind of settling tanks. The substances here are inactive and undergo only mineral transformations that are not associated with living matter. Such reserve funds are, for example, coal deposits and deposits of carbonate rocks on the seabed. Reserve funds can also be considered wood reserves in forest ecosystems, peat deposits, forest floor, humus, carbon reserves in the form of carbon dioxide in the atmosphere, hydrosphere, soil, chemical elements dissolved in water, the water itself.

In terms of the speed of movement of matter and stability, reserve funds are heterogeneous. Within the boundaries of the reserve fund, one can identify a mass of matter that is easily accessible to living organisms. Such matter, as a rule, is concentrated in highly mobile geospheres, in which flows of matter move much more energetically than in the rest of the reserve funds. This substance has a much higher chance of being involved in biological food chains. This mass of substance is called exchange fund.

The reserve funds of the atmosphere, hydrosphere and biosphere are usually easily accessible, matter is easily extracted from them and just as easily returned to them, therefore the processes occurring here are relatively stable. It is much more difficult to extract matter from the sedimentary cycle fund (from the lithosphere). Therefore, the processes taking place with the participation of this fund are less active and unstable. Here, the entry into the reserve proceeds at a faster pace than the extraction from it. The process of extracting and returning a substance to reserve funds is part of biogeochemical cycles.

In the process of evolution, biogeochemical cycles acquired an almost closed, circular character. Thanks to this, a certain constancy, dynamic balance of the composition, quantity and concentration of substances involved in the cycle is maintained. At the same time, due to the incomplete closure of the biological cycle, nitrogen and oxygen accumulate in the atmosphere, carbon compounds (oil, coal, gas) accumulate in the earth’s crust, and various salts accumulate in the ocean.

Thanks to high mobility atmosphere and the presence of a large exchange fund in it, some cycles (oxygen, carbon, nitrogen) have the ability to quickly self-regulate. For example, the resulting local concentrations of carbon dioxide quickly dissipate and are more quickly absorbed by vegetation.

Cycles occurring in the mode of sedimentary cycles (turnovers of sulfur, phosphorus, iron) are less active and little regulated. The bulk of these substances is concentrated in the sedentary lithosphere.

Both geological and biological cycles are characterized by irreversibility. New elements, new conditions, different rhythms and links of cycles are necessarily introduced into them. Constantly accumulating, these differences with each new cycle lead to noticeable changes even in biological systems. Some elements periodically fall out of the cycle and linger for one time or another in dead ends, which leads to the development of the biosphere.

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Ecology as a science
The term ECOLOGY was first used in 1866 by E. Haeckel to designate the science that studies the interdependencies between living organisms and

Emergence of global environmental problems
In the first stages of its existence, man collected the fruits of land ecosystems (forests, steppes, savannas, etc.), edible algae, mollusks, crustaceans, etc., caught fish and hunted. E

Demographic problems of the Earth
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Survival of humanity?
The growth of the population and the outstripping growth of the needs of society have set before humanity the global task of providing food with the necessary calorie content and composition, and adequate water.

Relationship between organism and environment
Basic concepts of general ecology. Fundamentals of the doctrine of the biosphere and its evolution. Structure of the biosphere. Environmental factors and their effects. Ecological niche and habitat. Biocenosis, biogeocenosis, ecosystem

Biosphere: properties, structure
The totality of all biogeocenoses (ecosystems) of our planet creates a giant global ecosystem called the biosphere. The term “biosphere” was first introduced into scientific literature in 1875

Levels of biological organization and trophic connections of living things
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Cycle of substances in nature
Thanks to the vital activity of living organisms, chemical elements continuously circulate in the biosphere, passing from the external environment into organisms and again into the external environment.

Oxygen cycle
In the pre-biological period of the Earth's existence, the atmosphere consisted mainly of water vapor, carbon dioxide, nitrogen and some other gases. Oxygen in more or less significant quantities per

Carbon cycle
The biological carbon cycle is simpler than the oxygen cycle, since it involves only organic compounds and carbon dioxide. The pools of carbon in the atmosphere are vast. The bulk of it is battery

Nitrogen cycle
Nitrogen is one of the main biogenic elements. The main reservoir of nitrogen gas is the atmosphere (78% of air volume). However, unlike carbon dioxide, the cycle

Phosphorus cycle
The so-called sedimentary cycles are adjacent to the cycles of basic chemical elements that have a gas phase. Mineral phosphorus is a rare element in the biosphere; its content in the earth’s crust is not

Functioning of the biosphere
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Natural resources
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Atmosphere. Air pollution
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Impact of human activities on the atmosphere
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Environmental standards and regulations
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Eco-protective equipment and technologies
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Cleaning emissions from gaseous impurities
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Hydrosphere. Impact of human activities on the hydrosphere
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Lithosphere pollution
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Fundamentals of environmental law and professional responsibility
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State security agencies
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Environmental assessment
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Legal liability for environmental violations
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Environmental monitoring
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Natural Resources and Nature Conservation
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Topic No. 5. Global cycles of basic nutrients

Questions:

1. Global and local water cycle.

2. Carbon cycle. Changes in the carbon dioxide balance over time: long-term trends and seasonal variations.

3. Oxygen cycle.

4. Nitrogen cycle. The role of microorganisms in maintaining the nitrogen cycle: ammonifying bacteria, nitrifying bacteria.

5. Phosphorus cycle, its low isolation. Phosphorus as a limiting factor.

6. Sulfur cycle. The role of microorganisms in maintaining the sulfur cycle. Pollution of water bodies with hydrogen sulfide.

Target: formation of ideas about the transboundary transfer of basic nutrients (water, carbon, oxygen, nitrogen, sulfur, phosphorus).

Solar energy on Earth causes two cycles of substances: large, or geological, most clearly manifested in the water cycle and atmospheric circulation, and small, biological (biotic), developing on the basis of the large one and consisting of a continuous, cyclical, but uneven in time and space, and accompanied by more or less significant losses in the natural redistribution of matter, energy and information within ecological systems of various levels of organization.

The most significant cycle on Earth in terms of transferred masses and energy consumption is the planetary hydrological cycle - the water cycle.

In liquid, solid and vapor states, water is present in all three main components of the biosphere: the atmosphere, the hydrosphere, and the lithosphere. All waters are united by the common concept of “hydrosphere”. The components of the hydrosphere are interconnected by constant exchange and interaction. Water, continuously moving from one state to another, makes small and large cycles. The evaporation of water from the surface of the ocean, the condensation of water vapor in the atmosphere and the precipitation on the surface of the ocean form a small cycle. When water vapor is carried by air currents to land, the cycle becomes much more complex. In this case, part of the precipitation evaporates and enters back into the atmosphere, the other feeds rivers and reservoirs, but ultimately returns to the ocean through river and underground runoff, thereby completing the large cycle.

The biotic (biological) cycle refers to the circulation of substances between soil, plants, animals and microorganisms. According to the definition of N.P. Remezov, L.E. Rodin and N.I. Bazilevich, the biotic (biological) cycle is the flow of chemical elements from soil, water and atmosphere into living organisms, the transformation of incoming elements into new complex compounds and their return back in the process of life activity with the annual fall of part of the organic matter or with completely dead organisms that are part of the ecosystem.

2. Carbon cycle. Changes in the carbon dioxide balance over time: long-term trends and seasonal variations

Migration of CO 2 in the biosphere occurs in two ways.

The first way is to absorb it during photosynthesis with the formation of glucose and other organic substances from which all plant tissues are built. Subsequently, they are transferred to food chains and form the tissues of all other living beings in the ecosystem. It should be noted that the probability of a single carbon “being” in the composition of many organisms during one cycle is small, because with each transition from one trophic level to another, there is a high probability that the organic molecule containing it will be broken down during cellular respiration to obtain energy. The carbon atoms then re-enter the environment as carbon dioxide, thus completing one cycle and preparing to begin the next. On land where there is vegetation, atmospheric carbon dioxide is absorbed during the daytime through the process of photosynthesis. At night, part of it is released by plants into the external environment. With the death of plants and animals on the surface, oxidation of organic substances occurs with the formation of CO 2.

Carbon atoms are also returned to the atmosphere when organic matter is burned. An important and interesting feature of the carbon cycle is that in distant geological epochs, hundreds of millions of years ago, a significant part of the organic matter created in the processes of photosynthesis was not used by either consumers or decomposers, but accumulated in the lithosphere in the form of fossil fuels: oil, coal, oil shale, peat, etc. These fossil fuels are mined in huge quantities to meet the energy needs of our industrial society. By burning it, we, in a sense, complete the carbon cycle.

In the second way, carbon migration is carried out by creating a carbonate system in various reservoirs, where CO 2 turns into H 2 CO 3, HCO 3, CO 2. With the help of calcium (or magnesium) dissolved in water, carbonates (CaCO 3) are precipitated through biogenic and abiogenic pathways. Thick layers of limestone are formed. According to A. B. Ronov, the ratio of buried carbon in photosynthetic products to carbon in carbonate rocks is 1:4. Along with the large carbon cycle, there are a number of small carbon cycles on the land surface and in the ocean.

Figure 1.13 - Water cycle

Global cycles of vitally important nutrients break up in the biosphere into many small cycles confined to the local habitats of various biological communities. They can be more or less complex and to varying degrees sensitive to various types of external influences. But nature has decreed that under natural conditions these biochemical cycles are “exemplary waste-free technologies.” Cycling covers 98-99% of nutrients and only 1-2% goes not even to waste, but to the geological reserve (Figure 1.14).

1.8 Fundamentals of biosphere sustainability

The stability of ecosystems and their entire biosphere depends on many factors (Figure 1.15), the essence of the most important of which is as follows:

Figure 1.15- Factors of biosphere stability

1. The biosphere uses external sources energy: solar energy and the energy of heating the earth’s interior to streamline its organization, effective use free energy without causing environmental pollution. The constant use of a certain amount of energy and its dissipation in the form of heat has created an evolutionarily established heat balance in the biosphere.

Biocenoses are characterized by the law (principle) of “energy conductivity”: the through flow of energy, passing through the trophic levels of the biocenosis, is constantly extinguished.

In 1942, R. Lindeman formulated the law of the energy pyramid or the law (rule) of 10%, according to which from one trophic level ecological pyramid moves to another higher level (“on the ladder” producer - consumer - decomposer) on average about 10% of the energy received at the previous level of the ecological pyramid.

2. The biosphere uses substances (mostly light nutrients) mainly in the form of gyres. Biogeochemical cycles of elements have been worked out evolutionarily and do not lead to the accumulation of waste.

3. There is a huge diversity of species and biological communities in the biosphere. Competitive and predatory relationships between species contribute to the establishment of equilibrium between them. At the same time, there are practically no dominant species with excessive numbers, which protects the biosphere from severe danger from internal factors.

Species diversity is a factor in increasing the resistance of ecosystems to external factors. The gene pool of wild nature is an invaluable gift, the potential of which has so far been used only to a small extent.

4. Almost all patterns characteristic of living matter have adaptive significance. Biosystems are forced to adapt to continuously changing living conditions. In the ever-changing environment of life, each type of organism is adapted in its own way. This is expressed by the rule of ecological individuality: no two species are identical.

The ecological specificity of species is emphasized by the so-called axiom of adaptability: each species is adapted to a strictly defined set of existence conditions specific to it - an ecological niche.

5. Self-regulation or maintenance of population size depends on a combination of abiotic and biotic factors. Each population interacts with nature as an integral system.

Population maximum rule: the number of natural populations is limited by the depletion of food resources and breeding conditions, the insufficiency of these resources and too short period accelerating population growth.

Any population has a strictly defined genetic, phenotic, sex-age and other structure. It cannot consist of fewer individuals than is necessary to ensure its resistance to environmental factors.

Principle minimum size is not a constant for any species, it is strictly specific for each population. Going beyond the minimum threatens the population with death: it will no longer be able to regenerate itself.

The destruction of each of these factors can lead to a decrease in the stability of both individual ecosystems and the biosphere as a whole.

Related information.

IN on a global scale biochemical cycles of water and carbon dioxide are, in our opinion, of the most importance for humanity. Biochemical cycles are characterized by the presence of small but mobile funds in the atmosphere.

The atmospheric pool of CO 2 in the cycle, compared to carbon reserves in the oceans, fossil fuels and other reservoirs of the earth's crust, is relatively small.

With the advent of scientific and technological progress, previously balanced carbon flows between the atmosphere, continents and oceans begin to enter the atmosphere in quantities that cannot be fully absorbed by plants.

Exist different estimates influence of human activity on the enrichment of the atmosphere with CO 2; however, all authors agree that the main carbon accumulators are forests, since forest biomass contains 1.5 times more CO 2, and humus contained in the soil contains 4 times more CO 2. than in the atmosphere.

Plants are a good regulator of CO 2 content in the atmosphere. Most plants are characterized by an increase in the intensity of photosynthesis with an increased content of carbon dioxide in the air

The Earth's photosynthetic "green belt" and the carbonate system of the sea maintain a constant level of CO 2 in the atmosphere. However, the rapid increase in the consumption of fossil fuels, as well as the decrease in the absorption capacity of the “green belt” lead to the fact that the CO 2 content in the atmosphere is gradually increasing. It is assumed that if the level of CO 2 in the atmosphere is doubled (before the onset of active human influence on the environment it was 0.29%), then an increase in global temperature by 1.5 - 4.5 ° C is possible. This can lead to the melting of glaciers and, as a result, to an increase in the level of the World Ocean, as well as to adverse consequences in agriculture. There is currently a national research program in the United States to Agriculture in case of warming or cooling of the climate.

In addition to CO 2, carbon monoxide CO is present in small quantities in the atmosphere - 0.1 parts per million and methane CH 4 - 1.6 parts per million. These carbon compounds are actively included in the cycle and therefore have a short residence time in the atmosphere: CO - about 0.1 year, CH 4 - 3.6 years, and CO 2 - 4 years. Carbon monoxide and methane are formed during incomplete or aerobic decomposition of organic matter and are oxidized to CO 2 in the atmosphere.

The accumulation of CO on a global scale does not seem to be realistic, but in cities where the air stagnates, there is an increase in the concentration of this compound, which negatively affects people's health.

Methane is produced by the decomposition of organic matter in marshy areas and shallow seas. According to some scientists, methane performs useful function- it maintains the stability of the ozone layer, which protects all life on Earth from the harmful effects of ultraviolet radiation.

The pool of water in the atmosphere, as shown in Figure 11, is small, and its turnover rate is higher and its residence time is shorter than CO 2. Like the CO 2 cycle, human activities affect the water cycle.

From an energy point of view, two parts of the CO 2 cycle can be distinguished: the “upper” part, which is driven by the Sun, and the “lower” part, in which energy is released. As already noted, about 30% of all the solar energy arriving at the Earth’s surface is spent on setting the water cycle in motion.

In ecological terms, special attention should be paid to two aspects of the water cycle. Firstly, the sea loses more water through evaporation than it receives through precipitation, that is, a significant part of the precipitation that supports land ecosystems, including agroecosystems, consists of water that has evaporated from the surface of the sea. Secondly, as a result of human activity, surface runoff increases and groundwater replenishment decreases. There are already areas where groundwater accumulated in the previous century is used. Therefore, in this case, water is a non-renewable resource. After groundwater is depleted, it will be delivered from other territories, which will require the investment of additional energy.

Nitrogen cycle

Nitrogen, like carbon, is part of atmospheric air and is present in it in the form of molecules (Md).

It plays an important role in the life of organisms. Like oxygen, nitrogen is necessary for animal respiration. Nitrogen is part of many organic compounds, primarily protein. In a protein molecule, it forms strong amide bonds with carbon or combines with hydrogen, present in the form of amine (- NH 3) or amide (- NH 2) groups.

The formation of amide (peptide) bonds (C - N bonds) is the main mechanism for the synthesis of protein molecules and peptides, which constitute the essence of all life on Earth.

A diagram reflecting the nitrogen cycle is shown in Fig. 6.

Rice. 6. Diagram of the nitrogen cycle. The main stages are highlighted and estimates of the amount of nitrogen involved in the main flows are given. Numbers in brackets are teragrams (Tg = 10 6 t) per year (according to Yu. Odum, 1986)

The source of nitrogen for autotrophs is nitrates (salts of nitric acid HNO 3), as well as atmospheric molecular nitrogen. Nitrate nitrogen enters the leaves through the root system of plants, where it is used for the synthesis of plant protein.

The second way in which nitrogen enters organisms is through direct nitrogen fixation from the atmosphere. This phenomenon is completely unique and characteristic of prokaryotes - nuclear-free microorganisms. Before 1950, only three taxa of microorganisms capable of fixing atmospheric nitrogen were known:

· free-living bacteria of the genera Azotobacter and Clostridium;

· symbiotic nodule bacteria Rhizobium genus;

· blue-green algae (cyanobacteria) of the genera Anabaena, Nostoc, as well as other members of the order Nostocales.

Then other types of organisms capable of fixing nitrogen from the atmosphere were discovered: purple bacteria of the genus Rhodospirillum, as well as soil bacteria close to Pseudomonas, actinomycetes from alder root nodules (Ainus, Ceanothus, Myrica and others). It was also found that blue-green algae of the genus Anabaena (it must be emphasized that these algae have the ability for heterotrophic nutrition and have other characteristics that allow them to be classified as bacteria) can be symbionts of fungi, mosses, ferns and even seed plants, and the ability to nitrogen fixation is beneficial for both participants. This amazing ability is why rice and pulses can be grown in the same field for several years without the need for nitrogen fertilizers.

The biochemical mechanism of direct fixation of atmospheric nitrogen is carried out with the participation of the enzyme nitrogenase, which catalyzes the splitting of the nitrogen molecule (N 2). This process requires significant energy expenditure to break the triple bond in the nitrogen molecule. The reaction occurs with the participation of a water molecule, resulting in the formation of ammonia (NH 3), for example, in legume nodules. To fix 1 g of nitrogen, bacteria spend about 10 g of glucose (about 40 kcal), synthesized during photosynthesis, i.e., the efficiency is only 10%.

This example also illustrates the benefits of symbiosis as a strategy of “cooperation” that promotes survival. It is not difficult to come to the idea that it is promising to develop varieties of agricultural crops that, using symbiosis with nitrogen-fixing microorganisms, would produce good yields without the use of fertilizers.

Nitrogen-containing organic compounds formed in plants through trophic chains enter the body of heterotrophs (animals), as well as into the soil after the plants die. In the soil they undergo decomposition with the participation of saprophages, are mineralized and then used by other plants. The final link in decomposition is ammonifier organisms that form ammonia (NH 3). Ammonia is involved in nitrification reactions, i.e. the formation of nitrites and their conversion to nitrates. Thus, the nitrogen cycle in the soil is constantly maintained.

At the same time, part of the nitrogen returns to the atmosphere due to the activity of denitrifying bacteria, which decompose nitrates to molecular nitrogen (N 2). As a result of bacterial denitrification, up to 50 - 60 kg of nitrogen evaporates annually from 1 hectare of soil.

The suspension of the nitrogen cycle may occur due to its accumulation in deep ocean sediments. In this case, nitrogen is switched off from the cycle for several million years. Losses are compensated by the supply of nitrogen gas during volcanic eruptions. Yu. Odum believes that volcanic eruptions are useful in this sense, and if “all volcanoes on Earth are blocked, then more people may well die from hunger than are now suffering from eruptions” (Odum Yu. Ecology. M.: Mir , 1986. T. 1. P. 209).

The nitrogen cycle is an example of a well-buffered gaseous cycle. It is an important factor limiting or controlling the number of organisms.

The nitrogen cycle has been studied in sufficient detail. It is known, in particular, that of the 10 9 tons of nitrogen that are absorbed annually in the biosphere, about 80% returns to the cycle from land and water, and only 20% of the required amount is “new” nitrogen coming from the atmosphere with rain and in a result of nitrogen fixation. On the contrary, from the nitrogen supplied to the fields with fertilizers, very little most of reused; the majority is lost with the harvest as a result of water removal and denitrification.

Phosphorus cycle

Phosphorus is also an element necessary for the nutrition of living organisms and plays a vital role in the growth and development of plants.

The reservoir of phosphorus, unlike nitrogen, is not the atmosphere, but rocks and other sediments formed in past geological eras. The mineral phosphorus is found in many rocks. It enters the hydrosphere during their erosion, is deposited as sediment in shallow waters, and is partially deposited in deep-sea silts.

In animals, phosphorus in the form of organic compounds (with proteins, in particular) is part of bones and other tissues. It also plays a role in the energy storage processes of cells in the form of adenosine triphosphoric and adenosine diphosphoric acids.

As a result of the decomposition of dead organisms and the mineralization of organic compounds, phosphorus in the form of phosphates (salts of orthophosphoric acid) is again used by plants and thereby again involved in the cycle.

The removal of phosphorus from the cycle occurs due to its accumulation in bottom sediments. The phosphorus cycle is an example of a simple sedimentary cycle with insufficient “buffering” and impaired self-regulation mechanisms due to anthropogenic impact on the environment. There is an opinion that the mechanisms for returning phosphorus to the cycle are insufficient and do not compensate for losses associated with technogenesis.

Human activities such as fishing and bird fishing lead to an imbalance in phosphorus balance. According to J. Hutchinson, only about 60,000 tons of elemental phosphorus are returned to land as a result of fishing (Quoted from: Odum Yu. Ecology. M.: Mir, 1986. Vol. 1). 1-2 million tons of phosphorus-containing rocks are mined annually for fertilizers. Moreover, most of this amount is washed off with water and removed from the circulation.

Currently, there is concern about the increase in the concentration of phosphates in aquatic ecosystems, which leads to their intensive overgrowing, degradation of ecosystems and ultimately to their death.

Phosphorus is widely used in agricultural technology in the form of phosphorus (mineral) fertilizers to increase soil fertility and crop yields. Thus, mineral phosphorus enters water and terrestrial ecosystems- due to the removal of dissolved phosphates with agricultural wastewater and runoff from fields where phosphate fertilizers were used, as well as the discharge of municipal and industrial wastewater.

According to J. Hutchinson, the turnover time of phosphorus in the water of small lakes (area 0.3 - 0.4 km 2 and depth 6 - 7 m) is 5.4 - 7.6 days, and large lakes (area 2 km 2, depth about 4 m) - 17 days. The turnover time in bottom sediments is much longer and is approximately 40 and 176 days, respectively. The difference in the value of the indicator is apparently explained by the fact that in small lakes the ratio of the surface of bottom sediments to the volume of water is greater. Thus, phosphorus is deposited in large, but not deep-water bodies of water, which greatly complicates the fight against their overgrowth.

Hydrobionts play a large role in self-purification. Thus, filter-feeding animals and detritivores make a significant contribution to the phosphorus cycle. For example, a population of filter feeders bivalves In 2.5 days, Modiolus demissus “returns” from the water as much “suspended” phosphorus as is contained in the water, i.e., the turnover time of “suspended” phosphorus is only 2.5 days (Odum Yu. Ecology. M.: Mir , 1986. T. 1. P. 219).

At the same time, as already noted, phosphorus is vital for plants and is one of the factors limiting the number of plant and other organisms included in trophic chains.

Sulfur cycle

The sulfur cycle diagram is shown in Fig. 8.

Mineral sulfur enters the soil as a result of the natural decomposition of sulfur and copper pyrites in rocks. It is transported with precipitation and enters terrestrial and aquatic ecosystems.

The sulfur cycle is characterized by an extensive reserve fund in soil and sediments and a smaller reserve in the atmosphere.

In the rapidly exchanging sulfur fund key role played by specialized groups of microorganisms (sulfate-oxidizing and sulfate-reducing).

Sulfur is a component of proteins and is part of a number of amino acids: cystine, cysteine, methionine. These amino acids are synthesized by plants using the mineral sulfur. Sulfur enters the body of animals with plant foods.

Rice. 8. The sulfur cycle, covering air, water and soil.

The "ring" in the center of the diagram illustrates the processes of oxidation (O) and reduction (R), due to which sulfur is exchanged between the pool of available sulfate (SO 4) and the pool of iron sulfides in soil and sediments. Specialized microorganisms perform reactions: H 2 S ® S 2 ® SO 4 - colorless, green and purple sulfur bacteria; SO 4 ®H 2 S (anaerobic reduction of sulfate) - Desulfovibrio; H 2 S ®SO 4 (aerobic sulfide oxidation) - thiobacillus; organic S in SO 4 and H 2 S are aerobic and anaerobic heterotrophic microorganisms, respectively. Primary production, of course, ensures the incorporation of sulfate into organic matter, and excretion by animals serves as a means of returning sulfate to the cycle. Sulfur dioxide (SO 2), released into the atmosphere when burning fossil fuels, especially coal, is one of the most dangerous components of industrial emissions (according to Yu. Odum, 1986).

As you know, everything structural components biospheres are closely interconnected by complex biogeochemical cycles of migration of substances and energy. Processes of mutual exchange and interaction take place on different levels: between geospheres (atmo-, hydro-, lithosphere), between natural areas, individual landscapes, their morphological parts, etc. However, a single general process of exchange of matter and energy dominates everywhere, a process that generates phenomena of different scales - from atomic to planetary. Many elements, having gone through a chain of biological and chemical transformations, return to the composition of the same chemical compounds in which they were at the initial moment. At the same time, the main driving force in the functioning of both global and small (as well as local) cycles is the living organisms themselves.
The role of biogeochemical cycles in the development of the biosphere is exceptionally great, since they ensure the repetition of the same organic forms with a limited volume of the initial substance participating in the cycles. Humanity can only be amazed at how wisely nature is structured, which itself tells the “unlucky Homo sapiens” how to organize the so-called waste-free production. Let us note, however, that in nature there are no completely closed cycles: any of them is simultaneously closed and open. An elementary example of a partial cycle is water that, having evaporated from the surface of the ocean, partially returns there.
There are complex relationships between individual small gyres, which ultimately leads to constant redistribution matter and energy between them, to eliminate some kind of asymmetric phenomena in the development of cycles. Thus, in the lithosphere, oxygen and silicon appeared in excess in a bound state, in the atmosphere in a free state, nitrogen and oxygen, in the biosphere - hydrogen, oxygen and carbon. It should also be noted that the bulk of carbon was concentrated in sedimentary rocks of the lithosphere,
where carbonates accumulated the bulk of carbon dioxide released into the atmosphere with volcanic eruptions.
We must not forget that there is a very close connection between space and the Earth, which, with a certain degree of convention, should be considered within the framework of the global circulation (since, as already noted, it is not closed). From space, our planet receives radiant energy (solar and cosmic rays), corpuscles of the Sun and other stars, meteorite dust, etc. The role of solar energy. In turn, the Earth gives back some of the energy, dissipates hydrogen into space, etc.
Many scientists, starting with V. Vernadsky, considering the global biogeochemical cycle of elements in nature as one of the most important factors in maintaining dynamic equilibrium in nature, distinguished two stages in the process of its evolution: ancient and modern. There is reason to believe that at the ancient stage the cycle was different, however, due to the absence of many unknowns (names of elements, their mass, energy, etc.), it is almost impossible to simulate the cycles of past geological eras (“former biospheres”).
To this it should be added that the main part of living matter consists of C, O, H, N, the main sources of plant nutrition are CO2, H2O and other minerals. Taking into account the importance of carbon, oxygen, hydrogen, nitrogen for the biosphere, as well as the specific role of phosphorus, we will briefly consider their global cycles, called “private” or “small”. (There are also local circulations associated with individual landscapes.)
Biogeochemical cycles individual elements. As you know, three chemical element- oxygen, carbon and hydrogen - make up 98% total mass living matter, with the first of them accounting for 70%, the second - 18 and the third - 10%. Unlike most of the oxygen and hydrogen present in organisms in the form of an aqueous substance (which is a solvent and a medium for biochemical reactions to occur), carbon is, in essence, a structure-forming component. Its ability to easily form carbon-carbon bonds is well known in science, resulting in polymer chains and rings that serve as the basis for the production of a variety of organic compounds.
During the long evolution of the biosphere, significant changes have occurred in the distribution of carbon. A huge amount of carbon turned out to be concentrated on the ocean floor in the form of poorly soluble calcium carbonate, as well as in the carbonates of the sedimentary lithosphere in the form of caustobioliths! etc. A lot of carbon is concentrated in the biomass of land and in sea organisms, in the atmosphere, in the humosphere. The driving force of the modern global carbon cycle is the biological cycle, which proceeds according to the following scheme: “bioassimilation of carbon from the atmosphere, aquatic or terrestrial environment by plants, consumption of organic compounds by animals and people, oxidation of organic substances to carbon dioxide in the process of respiration and decomposition of waste, return of carbon dioxide in atmosphere".
The carbon cycle on land and in the ocean is not the same: on land it mainly returns back to the atmosphere, in the ocean it remains mainly in solution. It is known that the ocean is a semi-autonomous system in gas exchange with the atmosphere, which indicates a slow exchange carbon dioxide in the ocean-atmosphere system. As for the land-ocean system, one-way migration of carbon predominates here in the form of the removal of this element from land in carbonate and organic compounds.
The circulation of oxygen, one of the most important elements in nature, is of enormous scientific interest, partly due to its growing consumption for industrial and other needs. There is an opinion that humanity will primarily face a shortage of oxygen, since it annually burns about a quarter of this element produced by terrestrial vegetation.
The beginning of intensive accumulation of oxygen in the atmosphere is associated with the spread of photosynthetic elements about 2 billion years ago. During the long evolution of the global oxygen cycle, the largest part of this element remained in the atmosphere, another part was dissolved in the ocean, and the third was recorded in the earth’s crust in the form of sulfates, carbonates, and various oxides.
The global nitrogen cycle is comparatively less well studied, mainly due to the difficulties in estimating the components of the cycle. It is still unknown exactly which specific organisms are capable of fixing nitrogen and converting it into such chemical compounds, which can be used by living organisms. Meanwhile, only fixed nitrogen, assimilated by living organisms of land and ocean, takes part in the biological cycle from the huge reserve of nitrogen in the atmosphere and sedimentary shell of the lithosphere. In general, under natural conditions, the processes of nitrogen fixation and release balance each other.
Of particular interest is the sedimentary cycle of phosphorus - a rather rare element in the biosphere (in the earth's crust its content does not exceed 1%). The scheme of the phosphorus cycle on land is as follows: “the absorption of inorganic phosphorus by plants, its conversion into the living matter of plants and animals (as well as people), the return of organic phosphates along with corpses, waste and excrement of living beings to the ground, the processing of phosphates by microorganisms.”
A completely different picture takes place in reservoirs, which is associated with the deposition of dead organisms at the bottom and their accumulation in bottom sediments. It is known that the decomposition of organic matter near the bottom often occurs in a slow manner due to insufficient oxygen supply. As a result, mineralized phosphorus forms an insoluble complex with ferric iron and thus is no longer available for absorption by aquatic organisms. However, this is not the only way to “remove” phosphorus from the global cycle. A large amount of it is carried into the World Ocean, but the rate of reverse transfer (by birds and fisheries products) is significantly less. The example of the global phosphorus cycle shows the danger posed by any ill-considered human impact on the natural course of biogeochemical processes in the biosphere.
Some of the cycles of elements that are especially important for the biosphere that we have examined show the enormous importance of maintaining the existing dynamic equilibria in a single global biogeochemical cycle.

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