Processes of self-purification of natural waters. Self-cleaning

One of the most valuable properties of natural waters is their ability to self-purify. Self-purification of water is the restoration of their natural properties in rivers, lakes and other water bodies, occurring naturally as a result of interrelated physicochemical, biochemical and other processes (turbulent diffusion, oxidation, sorption, adsorption, etc.). The ability of rivers and lakes to self-purify is closely dependent on many other natural factors, in particular physical and geographical conditions, solar radiation, the activity of microorganisms in water, the influence of aquatic vegetation and especially the hydrometeorological regime. The most intensive self-purification of water in reservoirs and streams occurs in the warm season, when biological activity in aquatic ecosystems is greatest. It flows faster on rivers with fast currents and dense thickets of reeds, reeds and cattails along their banks, especially in the forest-steppe and steppe zones of the country. A complete change of water in rivers takes on average 16 days, in swamps - 5 years, in lakes - 17 years.

Reducing the concentration of inorganic substances polluting water bodies occurs by neutralizing acids and alkalis due to the natural buffering of natural waters, the formation of sparingly soluble compounds, hydrolysis, sorption and precipitation. The concentration of organic substances and their toxicity are reduced due to chemical and biochemical oxidation. These natural methods of self-purification are reflected in the accepted methods of purifying contaminated water in industry and agriculture.

To maintain the required natural water quality in reservoirs and streams, the spread of aquatic vegetation, which acts as a kind of biofilter in them, is of great importance. The high cleaning ability of aquatic plants is widely used in many industrial enterprises both in our country and abroad. For this purpose, various artificial settling tanks are created, in which lake and swamp vegetation is planted, which effectively purifies polluted waters.

In recent years, artificial aeration has become widespread - one of the effective ways to purify contaminated water, when the self-purification process is sharply reduced due to a deficiency of oxygen dissolved in water. For this purpose, special aerators are installed in reservoirs and watercourses or at aeration stations before discharging contaminated water.

Protection of water resources from pollution.

The protection of water resources consists of prohibiting the discharge of untreated water into reservoirs and watercourses, creating water protection zones, promoting self-purification processes in water bodies, preserving and improving the conditions for the formation of surface and underground runoff in watersheds.

Several decades ago, rivers, thanks to their self-purifying function, managed to purify their waters. Now, in the most populated areas of the country, as a result of the construction of new cities and industrial enterprises, water use sites are located so densely that often wastewater discharge sites and water intakes are almost nearby. Therefore, more and more attention is being paid to the development and implementation of effective methods for purification and post-treatment of wastewater, purification and neutralization of tap water. In some enterprises, water-related operations are playing an increasingly important role. Costs for water supply, treatment and wastewater disposal are particularly high in the pulp and paper, mining and petrochemical industries.

Sequential wastewater treatment at modern enterprises involves primary, mechanical treatment (easily settling and floating substances are removed) and secondary, biological (biologically degradable organic substances are removed). In this case, coagulation is carried out - to precipitate suspended and colloidal substances, as well as phosphorus, adsorption - to remove dissolved organic substances and electrolysis - to reduce the content of dissolved substances of organic and mineral origin. Disinfection of wastewater is carried out through chlorination and ozonation. An important element of the cleaning process is the removal and disinfection of the resulting sediment. In some cases, the final step is distillation of water.

The most advanced modern treatment facilities ensure that wastewater is freed from organic contaminants by only 85-90% and only in some cases by 95%. Therefore, even after cleaning, it is necessary to dilute them 6-12 times, and often more, with clean water to maintain the normal functioning of aquatic ecosystems. The fact is that the natural self-purifying ability of reservoirs and watercourses is very insignificant. Self-purification occurs only if the discharged water has undergone complete purification, and in the water body it has been diluted with water in a ratio of 1:12-15. If wastewater enters reservoirs and watercourses in large volumes, and even more so untreated, the stable natural balance of aquatic ecosystems is gradually lost and their normal functioning is disrupted.

Recently, more and more effective methods of purification and post-treatment of wastewater after its biological treatment have been developed and implemented using the latest wastewater treatment methods: radiation, electrochemical, sorption, magnetic, etc. Improving wastewater treatment technology, further increasing the degree of purification are the most important tasks in areas of water protection from pollution.

The post-treatment of treated wastewater on agricultural irrigated fields (AIF) should be used much more widely. When post-treatment of wastewater at ZPO, no funds are spent on their industrial post-treatment, it creates the opportunity to obtain additional agricultural products, and water is significantly saved, since the intake of fresh water for irrigation is reduced and there is no need to spend water to dilute wastewater. When municipal wastewater is used in a waste treatment facility, the nutrients and microelements it contains are absorbed by plants faster and more completely than artificial mineral fertilizers.

Important tasks also include preventing pollution of water bodies with pesticides and toxic chemicals. To do this, it is necessary to speed up the implementation of anti-erosion measures, to create pesticides that would decompose within 1-3 weeks without preserving toxic residues in the crop. Until these issues are resolved, it is necessary to limit the agricultural use of coastal zones along watercourses or not to use pesticides in them. The creation of water protection zones also requires more attention.

In protecting water sources from pollution, the introduction of fees for wastewater discharge, the creation of comprehensive regional schemes for water consumption, water disposal and wastewater treatment, and the automation of control over water quality in water sources are important. It should be noted that complex regional schemes make it possible to move to the reuse and reuse of water, the operation of wastewater treatment facilities common to the region, as well as to automate the processes of managing the operation of water supply and sewerage systems.

In preventing pollution of natural waters, the role of protecting the hydrosphere is great, since the negative properties acquired by the hydrosphere not only modify the aquatic ecosystem and have a depressing effect on its hydrobiological resources, but also destroy land ecosystems, its biological systems, as well as the lithosphere.

It must be emphasized that one of the radical measures to combat pollution is to overcome the ingrained tradition of considering water bodies as wastewater receivers. Where possible, either water abstraction or wastewater discharge should be eliminated in the same watercourses and bodies of water.

Protection of atmospheric air and soil.

Specially protected natural areas. Protection of flora and fauna.

Effective form protection of natural ecosystems, as well as biotic communities are specially protected natural areas. They make it possible to preserve standards (samples) of untouched biogeocenoses, not only in some exotic, rare places, but also in all typical natural zones of the Earth.

TO specially protected natural areas(SPNA) refer to areas of land or water surface that, due to their environmental and other significance, are completely or partially withdrawn from economic use by Government decisions.

The Law on Protected Natural Areas, adopted in February 1995, established the following categories of these territories: a) state natural reserves, incl. biosphere; b) national parks; c) natural parks; d) state natural reserves; e) natural monuments; f) dendrological parks and botanical gardens.

Reserve- this is a specially protected by law space (territory or water area), which is completely withdrawn from normal economic use in order to preserve the natural complex in its natural state. Only scientific, security and control activities are permitted in nature reserves.

Today in Russia there are 95 nature reserves with a total area of 310 thousand square meters. km, which is about 1.5% of the entire territory of Russia. In order to neutralize the technogenic influence of adjacent territories, especially in areas with developed industry, protective zones are created around nature reserves.

Biosphere reserves (BRs) perform four functions: preserving the genetic diversity of our planet; conducting scientific research; monitoring the background state of the biosphere (ecological monitoring); environmental education and international cooperation.

It is obvious that the functions of a natural reserve are broader than those of any other type of protected natural areas. They serve as a kind of international standards, environmental standards.

A single global network of more than 300 biosphere reserves has now been created on Earth (in Russia there are 11). All of them work according to the agreed UNESCO program, conducting constant observations of changes in the natural environment under the influence of anthropogenic activities.

National Park- a vast territory (from several thousand to several million hectares), which includes both completely protected areas and zones intended for certain types of economic activities.

The goals of creating national parks are: 1) environmental (preservation of natural ecosystems); 2) scientific (development and implementation of methods for preserving the natural complex in conditions of mass admission of visitors) and 3) recreational (regulated tourism and recreation of people).

In Russia there are 33 national parks with a total area of about 66.5 thousand square meters. km.

Natural Park- a territory of special ecological and aesthetic value and used for organized recreation of the population.

Reserve is a natural complex that is designed to preserve one or more species of animals or plants with limited use of others. There are landscape, forest, ichthyological (fish), ornithological (birds) and other types of reserves. Usually, after the population density of protected species of animals or plants has been restored, the reserve is closed and one or another type of economic activity is allowed. In Russia there are now more than 1,600 state nature reserves with a total area of over 600 thousand square meters. km.

Natural monument- individual natural objects that are unique and irreproducible and have scientific, aesthetic, cultural or educational significance. These can be very old trees that were “witnesses” of some historical events, caves, rocks, waterfalls, etc. There are about 8 thousand of these in Russia, while in the territory where the monument is located, any activity that could destroy them is prohibited .

Dendrological parks and botanical gardens are collections of trees and shrubs created by man for the purpose of both preserving biodiversity and enriching the flora, and in the interests of science, study and cultural and educational work. They often carry out work related to the introduction and acclimatization of new plants.

For violation of the regime of specially protected natural areas, Russian legislation establishes administrative and criminal liability. At the same time, scientists and experts strongly recommend significantly increasing the area of specially protected areas. So, for example, in the USA the area of the latter is more than 7% of the country's territory.

The solution to environmental problems, and, consequently, the prospects for the sustainable development of civilization, is largely related to the competent use of renewable resources and various functions of ecosystems, and their management. This direction is the most important way for a fairly long-term and relatively sustainable use of natural resources in combination with the preservation and maintenance of the stability of the biosphere, and, consequently, the human environment.

Each biological species is unique. It contains information about the development of flora and fauna, which is of great scientific and applied importance. Since all the possibilities for using a given organism in the long term are often unpredictable, the entire gene pool of our planet (with the possible exception of some pathogenic organisms dangerous to humans) is subject to strict protection. The need to protect the gene pool from the standpoint of the concept of sustainable development (“coevolution”) is dictated not so much by economic considerations as by moral and ethical considerations. Humanity will not survive alone.

It is worth recalling one of B. Commoner’s environmental laws: “Nature knows best!” The possibilities of using the gene pool of animals, which were previously unforeseen, are now being demonstrated by bionics, thanks to which there are numerous improvements in engineering designs based on the study of the structure and functions of the organs of wild animals. It has been established that some invertebrates (mollusks, sponges) have the ability to accumulate large amounts of radioactive elements and pesticides. As a result, they can be bioindicators of environmental pollution and help humans solve this important problem.

Protection of the plant gene pool. As an integral part of the general problem of environmental protection, the protection of the plant gene pool is a set of measures to preserve the entire species diversity of plants - carriers of the hereditary heritage of productive or scientifically or practically valuable properties.

It is known that under the influence of natural selection and through sexual reproduction of individuals, the most beneficial properties for the species accumulate in the gene pool of each species or population; they are contained in gene combinations. Therefore, the tasks of using natural flora are of great importance. Our modern grain, fruit, vegetable, berry, fodder, industrial, ornamental crops, the centers of origin of which were established by our outstanding compatriot N.I. Vavilov, trace their ancestry either from wild ancestors, or are creations of science, but based on natural gene structures. By using the hereditary properties of wild plants, completely new types of useful plants have been obtained. By means of hybrid selection, perennial wheat and grain-forage hybrids were created. According to scientists' calculations, about 600 species of wild plants can be used in the selection of agricultural crops from the flora of Russia.

The protection of the plant gene pool is carried out by creating nature reserves, natural parks, and botanical gardens; formation of a gene pool bank of local and introduced species; studying biology, environmental needs and competitive ability of plants; ecological assessment of the plant habitat, forecasts of its changes in the future. Thanks to the reserves, Pitsunda and Eldar pine trees, pistachio, yew, boxwood, rhododendron, ginseng, etc. have been preserved.

Protection of the gene pool of animals. The change in living conditions occurring under the influence of human activity, accompanied by direct persecution and extermination of animals, leads to a depletion of their species composition and a reduction in the number of many species. In 1600 There were approximately 4,230 species of mammals on the planet; to date, 36 species have disappeared, and 120 species are in danger of extinction. Of the 8,684 bird species, 94 have disappeared and 187 are endangered. The situation is no better with subspecies: since 1600, 64 subspecies of mammals and 164 subspecies of birds have disappeared, 223 subspecies of mammals and 287 subspecies of birds are in danger.

Protection of the gene pool of humanity. For this purpose, various scientific directions have been created, such as:

1) ecotoxicology- a section of toxicology (the science of poisons), which studies the ingredient composition, characteristics of distribution, biological action, activation, deactivation of harmful substances in the environment;

2) medical genetic counseling in special medical institutions to determine the nature and consequences of the action of ecotoxicants on the human genetic apparatus in order to give birth to healthy offspring;

3) screening- selection and testing for mutagenicity and carcinogenicity of environmental factors (the natural environment around humans).

Environmental pathology- the doctrine of human diseases, in the occurrence and development of which the leading role is played by unfavorable environmental factors in combination with other pathogenic factors.

Fundamental directions of environmental protection.

Standardization of environmental quality. Protection of the atmosphere, hydrosphere, lithosphere, biotic communities. Eco-protective equipment and technologies.

Self-purification of water in reservoirs is a set of interconnected hydrodynamic, physicochemical, microbiological and hydrobiological processes leading to the restoration of the original state of a water body.

Among the physical factors, dilution, dissolution and mixing of incoming contaminants are of paramount importance. Good mixing and reduced concentrations of suspended particles are ensured by the fast flow of rivers. The self-purification of reservoirs is facilitated by the settling of insoluble sediments to the bottom, as well as the settling of polluted waters. In zones with a temperate climate, the river cleans itself after 200-300 km from the place of pollution, and in the Far North - after 2 thousand km.

Water disinfection occurs under the influence of ultraviolet radiation from the sun. The disinfection effect is achieved by the direct destructive effect of ultraviolet rays on protein colloids and enzymes of the protoplasm of microbial cells, as well as spore organisms and viruses.

Among the chemical factors of self-purification of reservoirs, oxidation of organic and inorganic substances should be noted. The self-purification of a reservoir is often assessed in relation to easily oxidized organic matter or by the total content of organic matter.

The sanitary regime of a reservoir is characterized primarily by the amount of oxygen dissolved in it. It should be at least 4 mg per 1 liter of water at any time of the year for reservoirs of the first and second types. The first type includes reservoirs used for drinking water supply to enterprises, the second type includes those used for swimming, sporting events, and those located within populated areas.

Biological factors of self-purification of a reservoir include algae, mold and yeast. However, phytoplankton does not always have a positive effect on self-purification processes: in some cases, the massive development of blue-green algae in artificial reservoirs can be considered a process of self-pollution.

Representatives of the animal world can also contribute to the self-purification of water bodies from bacteria and viruses. Thus, the oyster and some other amoebas adsorb intestinal and other viruses. Each mollusk filters more than 30 liters of water per day.

The cleanliness of water bodies is unthinkable without protecting their vegetation. Only on the basis of deep knowledge of the ecology of each reservoir and effective control over the development of the various living organisms inhabiting it can positive results be achieved, transparency and high biological productivity of rivers, lakes and reservoirs ensured.

Other factors also adversely affect the self-purification processes of water bodies. Chemical pollution of water bodies with industrial wastewater, nutrients (nitrogen, phosphorus, etc.) inhibits natural oxidative processes and kills microorganisms. The same applies to the discharge of thermal wastewater by thermal power plants.

A multi-stage process, sometimes extending over a long time, is self-purification of oil. Under natural conditions, the complex of physical processes of self-purification of water from oil consists of a number of components: evaporation; settling of lumps, especially those overloaded with sediment and dust; sticking together of lumps suspended in the water column; floating of lumps forming a film with inclusions of water and air; reducing the concentrations of suspended and dissolved oil due to settling, floating and mixing with clean water. The intensity of these processes depends on the properties of a particular type of oil (density, viscosity, coefficient of thermal expansion), the presence of colloids, suspended and transportable plankton particles, etc. in water, air temperature and solar illumination.

There is a continuous exchange of matter and energy between the components of the aquatic ecosystem during its functioning. This exchange is cyclical in nature with varying degrees of closure, accompanied by the transformation of matter under the influence of physical, chemical and biological factors. During transformation, a gradual decomposition of complex substances into simple ones can occur, and simple substances can be synthesized into complex ones. Depending on the intensity of the external impact on the aquatic ecosystem and the nature of the processes, either the aquatic ecosystem is restored to background states (self-purification), or the aquatic ecosystem moves to another stable state, which will be characterized by different quantitative and qualitative indicators of biotic and abiotic components. If the external influence exceeds the self-regulating capabilities of the aquatic ecosystem, its destruction may occur. Self-purification of aquatic ecosystems is a consequence of the ability to self-regulate. The supply of substances from external sources is an impact that the aquatic ecosystem is able to withstand within certain limits through intrasystem mechanisms. In an ecological sense, self-purification is a consequence of the processes of inclusion of substances entering a water body into biochemical cycles with the participation of biota and factors of inanimate nature. The cycle of any element is composed of two main funds - a reserve fund, formed by a large mass of slowly changing components, and an exchange (circulation) fund, which is characterized by rapid exchange between organisms and their habitat. All biochemical cycles can be divided into two main types - with a reserve fund in the atmosphere (for example, nitrogen) and with a reserve fund in the earth's crust (for example, phosphorus).

Self-purification of natural waters is carried out due to the involvement of substances coming from external sources into continuously occurring transformation processes, as a result of which the received substances are returned to their reserve fund.

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The transformation of substances is the result of various simultaneously operating processes, among which physical, chemical and biological mechanisms can be distinguished. The magnitude of the contribution of each mechanism depends on the properties of the impurity and the characteristics of a particular ecosystem.

Physical mechanisms of self-cleaning.Gas exchange at the atmosphere-water interface. Thanks to this process, substances that have a reserve fund in the atmosphere enter the water body, and these substances are returned from the water body to the reserve fund. One of the important special cases of gas exchange is the process atmospheric reaeration, due to which a significant portion of oxygen enters the water body. The intensity and direction of gas exchange are determined by the deviation of the gas concentration in water from the saturation concentration C\ The value of the saturation concentration depends on the nature of the substance and the physical conditions in the water body - temperature and pressure. At concentrations greater than C, the gas evaporates into the atmosphere, and at concentrations less than Cs, the gas is absorbed by the water mass.

Sorption- absorption of impurities by suspended substances, bottom sediments and surfaces of aquatic organisms. Colloidal particles and organic substances in a non-dissociated molecular state are sorbed most energetically. The process is based on the phenomenon of adsorption. The rate of accumulation of a substance per unit mass of the sorbent is proportional to its unsaturation for the given substance and the concentration of the substance in water and inversely proportional to the content of the substance in the sorbent. Examples of regulated substances subject to sorption are heavy metals and surfactants.

Sedimentation and resuspension. Water bodies always contain a certain amount of suspended substances of inorganic and organic origin. Sedimentation is characterized by the ability of suspended particles to fall to the bottom under the influence of gravity. The process of transition of particles from bottom sediments into a suspended state is called resuspension. It occurs under the influence of the vertical component of the turbulent flow velocity.

Chemical mechanisms of self-cleaning.Photolysis- transformation of molecules of a substance under the influence of light absorbed by them. Special cases of photolysis are photochemical dissociation - the disintegration of particles into several simpler ones and photoionization - the transformation of molecules into ions. Of the total amount of solar radiation, about 1% is used in photosynthesis, from 5% to 30% is reflected by the water surface. The main part of solar energy is converted into heat and participates in photochemical reactions. The most effective part of sunlight is ultraviolet radiation. Ultraviolet radiation is absorbed in a layer of water about 10 cm thick, but due to turbulent mixing it can penetrate into deeper layers of water bodies. The amount of a substance subjected to photolysis depends on the type of substance and its concentration in water. Of the substances entering water bodies, humic substances are susceptible to relatively rapid photochemical decomposition.

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Hydrolysis- ion exchange reaction between various substances and water. Hydrolysis is one of the leading factors in the chemical transformation of substances in water bodies. A quantitative characteristic of this process is the degree of hydrolysis, which is understood as the ratio of the hydrolyzed part of the molecules to the total salt concentration. For most salts it is a few percent and increases with increasing dilution and water temperature. Organic substances are also subject to hydrolysis. In this case, hydrolytic cleavage most often occurs through the bond of a carbon atom with other atoms.

Biochemical self-purification is a consequence of the transformation of substances carried out by hydrobionts. As a rule, biochemical mechanisms make the main contribution to the process of self-purification, and only when aquatic organisms are oppressed (for example, under the influence of toxicants) do physicochemical processes begin to play a more significant role. Biochemical transformation of substances occurs as a result of their inclusion in trophic networks and is carried out during the processes of production and destruction.

Primary production plays a particularly important role, since it determines the majority of intra-reservoir processes. The main mechanism of new formation of organic matter is photosynthesis. In most aquatic ecosystems, phytoplankton are the key primary producers. During the process of photosynthesis, solar energy is directly transformed into biomass. A by-product of this reaction is free oxygen produced by photolysis of water. Along with photosynthesis, plants undergo respiration processes that consume oxygen.

Autotrophic production and heterotrophic destruction are two of the most important aspects of the transformation of matter and energy in aquatic ecosystems. The nature and intensity of production-destructive processes and, consequently, the mechanism of biochemical self-purification are determined by the structure of a particular ecosystem. Therefore, they can vary significantly in different water bodies. Moreover, within the same body of water there are different zones of life (ecological zones), differing in the communities of organisms inhabiting them. These differences are due to changes in living conditions during the transition from surface to depth and from coastal zones to open parts.

In watercourses, due to intense mixing and shallow depths, vertical zonation is not expressed. Based on the flow cross-section, a distinction is made between ripal - the coastal zone and medial - the open zone corresponding to the core of the river. The ripal is characterized by low flow velocities, thickets of macrophytes, and high values of the quantitative development of hydrobionts. In the medial, the speed of water movement is higher, the quantitative development of hydrobionts is lower. According to the longitudinal profile, zones of reaches and zones of rifts are distinguished. In the zone of reaches characterized by a slow flow, the population is quantitatively richer, but qualitatively poorer. The opposite picture is typical for riffles.

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Complex environmental conditions affect self-purification processes in watercourses. Slow currents are characterized by favorable conditions for photosynthesis, intensive processes of transformation of substances, and sedimentation processes. Zones with high velocities are characterized by intense processes of mixing, gas exchange and destruction of substances.

In reservoirs, ecological zonation is more clearly manifested than in watercourses. In water bodies, along the horizontal profile, the littoral zone is distinguished - a zone of coastal shallow waters and the pelagic zone (limnic zone) - a zone of open water. In deep reservoirs, three zones are distinguished vertically in the pelagic water mass - epilimnion, metalimnion and hypolimnion. The metalimnion, or thermocline, is the zone separating the epilimnion and hypolimnion. It is characterized by a sharp decrease in water temperature (1 degree per 1 m depth). Above the metalimnion is the epilimnion. The epilimnion is characterized by the predominance of production processes. With increasing depth, as photosynthetically active radiation (PAR) decreases, the intensity of photosynthesis decreases. The depth at which production becomes equal to destruction is called the compensation horizon. Above it is the trophogenic zone, where production processes predominate, and below it is the tropholytic zone, where respiration and decomposition processes predominate. The trophogenic zone is located in the epilimnion, and the tropholitic zone, as a rule, covers the metalimnion and hypolimnion.

In the bottom zone of reservoirs, in addition to the littoral zone, there is a profundal zone - a deep-water part that approximately coincides with the part of the reservoir bed filled with hypolimnion waters.

Thus, in reservoirs it is possible to distinguish zones with a predominance of photosynthetic products and zones where only processes of destruction of substances occur. In the hypolimnion, especially in winter and summer, anaerobic conditions are often observed, which reduces the intensity of self-purification processes. On the contrary, in the littoral zone the temperature and oxygen regimes are favorable for intensive self-purification processes.

Eutrophication, which is understood as the hyperproduction of organic matter in a water body under the influence of external (allochthonous) and intra-water body (autochthonous) factors, is one of the serious environmental problems faced by almost all developed countries. Almost any water body is subject to eutrophication, but it is most pronounced in water bodies. Eutrophication of water bodies is a natural process, its development is assessed on a geological time scale. As a result of anthropogenic input of nutrients into water bodies, there has been a sharp acceleration of eutrophication. The result of this process, called anthropogenic eutrophication, is a decrease in the time scale of eutrophication from thousands of years to decades. Eutrophication processes are especially intense in urbanized areas, which has made them one of the most characteristic features of urban water bodies.

Section 3. Water environment of the city

The trophicity of a water body corresponds to the level of input of organic matter or the level of its production per unit of time and, thus, is an expression of the combined action of organic matter formed during photosynthesis and supplied from the outside. According to the level of trophicity, two extreme types of water bodies are distinguished - oligotrophic and eutrophic. The main differences between these two types of water bodies are given in table 3.14.

Table 3.14. Characteristics of oligotrophic and eutrophic reservoirs

	Condition of the reservoir
Hapaktvpistics
	oligotrophic	eutrophic
Physico-chemical characteristics
Dissolved oxygen concentration	High	Low
in the hypolimnion
Concentration of nutrients	Low	High
Suspended solids concentration	Low	High
Light penetration	good	Bad
Depth	Big	Small
Biological characteristics
Productivity	Low	High
Diversity of aquatic species	Small	Big
Phytoplankton:
biomass	Small	Big
daily migrations	Intensive	Limited
bloom	Rare	Frequent
characteristic groups	Diatoms,	Green, blue
	green algae	green algae

The main mechanism of the natural eutrophication process is siltation of water bodies. Anthropogenic eutrophication occurs due to the entry of excess amounts of nutrients into water as a result of economic activity. The high content of nutrients stimulates autotrophic hyperproduction of organic matter. The result of this process is water bloom due to excessive development of algal flora. Among the nutrients entering water, nitrogen and phosphorus have the greatest influence on eutrophication processes, since their content and ratio regulate the rate of primary production. The remaining biogenic elements, as a rule, are contained in water in sufficient quantities and do not affect the eutrophication processes. For lakes, the limiting element is most often phosphorus, and for watercourses it is nitrogen.

A water body is assigned to a certain trophic level based on the intake of organic matter. Since the specified

Ecology of the city

In practice, this parameter is difficult to control; other characteristics of the aquatic ecosystem, which are closely related to the trophic state of the reservoir, are used as indicators of the trophic level. These characteristics are called indicator characteristics. Most often in modern practice, the quantities of nutrients supplied, the concentrations of nutrients in a water body, the rate of oxygen depletion in the hypolimnion, water transparency, and phytoplankton biomass are used as indicators. Phytoplankton are the main primary producers in most aquatic ecosystems. Therefore, the ecological state of most water bodies is determined by phytoplankton and depends on a number of physical, chemical and biological environmental factors.

Physical factors of eutrophication.Illumination. The dependence of primary production on illumination is shown in rice. 3.18. The penetration of light into the water column is determined by a number of factors. Incident light is absorbed by the water itself and colored substances dissolved in it, and is scattered by suspended substances in the water. The depth at which the illumination is 5% of the illumination at the surface is called the euphotic horizon. Above the euphotic horizon is the euphotic zone. The change in primary production with depth depends on changes in illumination. In the summer months, the maximum productivity may shift in depth. This is explained by excess illumination on the surface, leading to the suppression of phytoplankton, as a result of which the best conditions for its existence are created in deeper layers.

Temperature influences the physical and biological processes of eutrophication. It determines the degree of oxygen saturation of water; the temperature profile affects the intensity of vertical turbulence and thus affects the transfer of nutrients from the bottom areas to the epilimnion. Temperature also affects the amount of primary production (Fig. 3.19). The optimal temperature varies depending on the type of organism, but in most cases lies in the range of 20-25° C.

The ecological state of water bodies is largely related to the processes of self-purification - a natural reserve for restoring the original properties and composition of water.
The main processes of self-purification lead to:

transformation (transformation) of pollutants into harmless or less harmful substances as a result of chemical and especially biochemical oxidation;
relative purification - the transition of pollutants from the water column to bottom sediments, which in the future can serve as a source of secondary water pollution;
removal of pollutants outside the water body as a result of evaporation, release of gases from the water column or wind removal of foam.

The transformation of pollutants plays the greatest role in the process of water self-purification. It covers non-conservative pollutants whose concentrations change as a result of chemical, biochemical and physical processes in water bodies. Non-conservatives mainly include organic and biogenic substances. The intensity of oxidation of a transformed pollutant depends, first of all, on the properties of this substance, water temperature, and conditions for the supply of oxygen to the water body.

Temperature conditions can be assessed by the average water temperature for three summer months, which sufficiently reflects the conditions for the entire warm period (the water temperature on Russian rivers in the winter months remains almost the same, close to 0°C). According to this indicator, rivers and reservoirs are divided into three groups: with temperatures below 15°C, from 15 to 20°C and above 20°C.

The conditions for the supply of oxygen are determined mainly by the intensity of water mixing and duration, which has a fairly close correlation with summer.

The intensity of water mixing in rivers is estimated approximately, depending on the nature of the terrain through which they flow, and for lakes and reservoirs - by the shallowness coefficient g, depending on the area of the water surface and the average depth of the reservoir. According to these assessment criteria, rivers and reservoirs are divided into 4 groups: with strong, significant, moderate and weak mixing. Based on the combination of temperature and mixing conditions, 4 categories of conditions for the transformation of pollutants in surface waters are distinguished: favorable, average, unfavorable and extremely unfavorable. Assessment of water self-purification based on these indicators is unacceptable neither for the largest transzonal rivers (Volga, Yenisei, Lena, etc.), nor for small rivers (with a basin area of less than 500–1000 km2), since the water temperature and mixing conditions in them are very different from background values.

An important role in the self-purification of water is also played by the physical process of diluting the content of pollutants, the concentration of which in river water decreases with increasing water flow in the river. The role of dilution is not only to reduce the concentration of pollutants, but also to reduce the likelihood of poisoning (toxicosis) of aquatic organisms responsible for the biochemical degradation of pollutants. An indicator of the conditions for dilution of pollutants is the average annual water flow for a river, and the total water flow of the tributaries flowing into it for a reservoir. According to this indicator, all rivers and reservoirs are divided into 6 groups (with water flow from less than 100 to more than 10,000 m3/s). Based on the combination of two most important conditions - the transformation of pollutants and water consumption - it is possible to approximately assess the conditions for self-purification of surface waters from pollutants and combine them into 5 categories: from “most favorable” to “extremely unfavorable”. Self-purification conditions taking into account dilution for transzonal rivers were calculated individually for individual sections of each river. The upper reaches of medium and large rivers, characterized by weak dilution capacity, are classified as rivers with “extremely unfavorable” self-purification conditions.
There are certain spatial patterns in the conditions for the transformation of pollutants in Russian surface waters. Thus, water bodies with “extremely unfavorable” conditions are located in low-lying tundra and forest-tundra areas. All deep-water lakes (Ladoga, Onega, Baikal, etc.) and reservoirs with particularly slow water exchange belong to the same group. And territories with “favorable” transformation conditions are confined to the Central Russian and Volga Uplands, the foothills of the North Caucasus.

Taking into account the dilution of pollution, most medium-sized and almost all small rivers in Russia are characterized by “extremely unfavorable” self-purification conditions. The “most favorable” conditions for self-purification are characterized by sections of the Ob, Yenisei, Lena and Amur rivers, which fall into the highest category of water content (more than 10,000 m3/s) with water temperatures in the average range (15–20°C), as well as the lower reaches of the Volga with a temperature above 20°C. The following reservoirs have the same category of conditions: Volgogradskoye, Tsimlyanskoye, Nizhnekamskoye.

Analysis of territorial differences in the conditions of self-purification of rivers and reservoirs makes it possible to approximately assess the degree of danger of their pollution from the influx of pollutants. This, in turn, can serve as a basis for establishing the level of restrictions on wastewater discharge in cities and developing recommendations on the size of the reduction in dispersed input of pollutants into surface waters.

Negative natural factors include the presence of steep slopes and flooded areas that are unstable to additional anthropogenic load. Negative technogenic factors should be considered high clutter in certain areas, the influence of polluted and insufficiently treated wastewater from residential areas, industrial zones and enterprises, affecting the quality of water bodies. Consequently, the condition of the reservoirs does not meet the requirements for cultural and community facilities. In addition, excess air pollution along highways is typical for almost the entire territory.

II. Water bodies, being natural and natural-technogenic elements of landscape-geochemical systems, in most cases are the final link in the runoff accumulation of most of the mobile technogenic substances. In landscape-geochemical systems, substances from higher levels to lower hypsometric levels are transported with surface and underground runoff, and vice versa (from low to higher levels) by atmospheric flows and only in some cases by flows of living matter (for example, during a massive escape from reservoirs of insects after completion of the larval stage of development taking place in water, etc.).

Landscape elements representing the initial, most highly located links (occupying, for example, local watershed surfaces) are geochemically autonomous and the intake of pollutants into them is limited, with the exception of their entry from the atmosphere. Landscape elements that form lower stages of the geochemical system (located on slopes and in depressions of the relief) are geochemically subordinate or heteronomous elements that, along with the input of pollutants from the atmosphere, receive part of the pollutants that come with surface and groundwater from higher-lying parts of the landscape -geochemical cascade. In this regard, pollutants formed in the catchment area, due to migration in the natural environment, sooner or later enter water bodies mainly with surface and groundwater runoff, gradually accumulating in them.

5 Basic processes of self-purification of water in a water body

Self-purification of water in reservoirs is a set of interconnected hydrodynamic, physico-chemical, microbiological and hydrobiological processes leading to the restoration of the original state of a water body.

6 Measures to intensify the processes of self-purification of a water body

Self-purification of water is an indispensable link in the water cycle in nature. Pollution of any type during self-purification of water bodies ultimately turns out to be concentrated in the form of waste products and dead bodies of microorganisms, plants and animals that feed on them, which accumulate in the silt mass at the bottom. Water bodies in which the natural environment can no longer cope with incoming pollutants are degraded, and this occurs mainly due to changes in the composition of biota and disruptions in food chains, primarily the microbial population of the water body. Self-purification processes in such water bodies are minimal or stop completely.

Such changes can only be stopped by purposefully influencing factors that contribute to reducing the generation of waste and reducing pollution emissions.

This task can be solved only by implementing a system of organizational measures and engineering and reclamation work aimed at restoring the natural environment of water bodies.

When restoring water bodies, it is advisable to begin the implementation of a system of organizational measures and engineering and reclamation work with the arrangement of the catchment area, and then carry out the cleaning of the water body, followed by the development of coastal and floodplain areas.

The main objective of the environmental protection measures and engineering and reclamation work in the catchment area is to reduce the generation of waste and prevent unauthorized discharge of pollutants onto the topography of the catchment area, for which the following activities are carried out: introduction of a system for regulating waste generation; organization of environmental control in the system of production and consumption waste management; conducting an inventory of facilities and locations for production and consumption waste; reclamation of disturbed lands and their improvement; tightening of fees for unauthorized discharge of pollutants onto the terrain; introduction of low-waste and non-waste technologies and recycling water supply systems.

Environmental protection measures and work carried out in coastal and floodplain areas include work on leveling the surface, leveling or terracing slopes; construction of hydraulic engineering and recreational structures, strengthening of banks and restoration of stable grass cover and tree and shrub vegetation, which subsequently prevent erosion processes. Landscaping work is carried out to restore the natural complex of a water body and transfer most of the surface runoff into the underground horizon for the purpose of its purification, using rocks of the coastal zone and floodplain lands as a hydrochemical barrier.

The banks of many water bodies are littered, and the waters are polluted with chemicals, heavy metals, petroleum products, floating debris, and some of them are eutrophicated and silted. It is impossible to stabilize or activate self-purification processes in such water bodies without special engineering and reclamation intervention.

The goal of carrying out engineering and reclamation measures and environmental protection work is to create conditions in water bodies that ensure the effective functioning of various water purification structures, and to carry out work to eliminate or reduce the negative impact of sources of distribution of pollutants of both off-channel and river-bed origin.