PRINCIPLES OF FUNCTIONING OF LAKES AND LAKE ECOSYSTEMS

1. Some physical processes that form the structure of water in lakes

Many modern research and modeling methods treat the lake as a simple “black box” or “well-mixed reactor”, where, in the process of research, scientists study the relationships between biochemical processes and the physical stratification (layered structure) in them (Henderson-Sellers, Markland, 1990 ).

Fresh water is a unique substance. It has the greatest density at 4°C, which protects even relatively shallow bodies of water from freezing, since colder water and the ice that then forms have a lower density and “float” on the surface. This relationship between the density and temperature of water is due to the peculiarities of its molecular structure. As a result, a thermally stratified reservoir is formed both in summer and (possibly) in winter (reverse stratification).

Lake stratification has a seasonal cycle. In spring and summer, as the air temperature rises, the lakes warm up. In this case, the surface layers receive more heat than the deeper layers. Since, as a result of this process, the waters of the surface layer become less dense and less stable, stratification of the water column occurs. As this process develops in spring and summer, the depth of the heated layer increases; this is facilitated by convective turbulent mixing and molecular thermal conductivity, wind mixing and increasing air temperatures. The layer formed in this way is called the epilimnion, its depth rarely exceeds 25 m. Within the epilimnion, wind and convective mixing distributes heat throughout the depth, creating relatively isothermal conditions. For these reasons, the epilimnion is often called a mixing layer (Chebotarev, 1955; Zenin and Belousova, 1988; Henderson-Sellers and Markland, 1990).

Below the epilimnion, water temperatures drop rapidly because the lower layers receive significantly less solar heat and are not subject to wind mixing. This area of ​​sharp decrease in temperature, located above the hypolimnion, is called the metalimnion (thermocline - confined to the depth at which the greatest temperature changes are observed).

Hypolimnion - includes the coldest waters and is relatively isothermal. In this area, temperature changes are minimal throughout the year and there are no currents. The thermocline (usually 2–5 m thick) is an effective barrier to the mixing of waters between the epi- and hypolimnion due to sharp temperature gradients. As a result, the lake as a whole is a dynamically stable system.

In autumn, when the air temperature drops, the lake begins to release heat into the atmosphere. During cooling, the density of the upper layers increases, and they move through the epilimnion to the depth of equilibrium. This type of instability causes currents to develop that eventually break the thermocline and lead to isothermal conditions in the lake. The consequence of this “revolution” is excessive turbidity of the water caused by the resuspension of bottom sediments, as well as an increase in the availability of nutrients in the euphotic zone (in which the intensity of photosynthesis exceeds the intensity of plant respiration); The depth of this zone (layer thickness) in different types of reservoirs has its own specific parameters.

In some small lakes, the epilimnion can be completely replaced by the hypolimnion (or vice versa), so that the lake becomes relatively uniform throughout the year - homothermy is observed. In such lakes, continuous mixing continues, caused by convection and turbulence induced by wind action, which contributes to prolonged turbidity of the water (Chebotarev, 1955; Zenin, Belousova, 1988; Henderson-Sellers, Markland, 1990).

Once a uniform temperature profile is achieved, the lake continues to cool and convective currents reach the bottom. Uniformity is thus established and maintained until the temperature of maximum water density is reached (this phenomenon never occurs in lakes located in warm climate zones). If the temperature of the surface waters is below 4°C, then the anomalous variations in water density with temperature determine that these colder waters will become less dense, leading to an increase in stability, in which the temperature profile shows reverse stratification. The surface waters will eventually freeze. However, due to the fact that this cooler layer is located on the surface, the underlying layers will have a temperature of about 4°C and will not freeze. Thus, the lake acquires ice cover. It forms only when the water of a lake, frozen to a certain depth, loses enough heat. Ice effectively protects water masses from wind mixing.

In the spring, when the amount of heat increases, the ice melts (if there was any, of course). As the lake surface warms, an unstable temperature profile reappears, but subsequent spring convective movements penetrate to a shallower depth than in autumn. After some time, during a period approximately corresponding to the spring equinox, the water masses again become uniform in temperature. This moment corresponds to the last stage of the full annual cycle of stratification (Chebotarev, 1955; Zenin, Belousova, 1988; Henderson-Sellers, Markland, 1990).
Lakes where autumn and spring convective mixing of waters are observed are called dimictic. Lakes where only spring mixing of waters is observed and the water temperature never exceeds 4°C are called cold monomictic (in warm climatic zones, where the water always exceeds 4°C, lakes are warm monomictic).

The mixing of waters in lakes is therefore a function (consequence) of their location. In tropical and equatorial regions, where solar heat input varies little throughout the year, the hypolimnion is rarely much colder than the epilimnion; therefore, even slight cooling causes convective movements of water due to a weak thermocline. Such lakes are called polymictic (water mixing here is often the result of strong winds and slight seasonal changes in air temperature). There are other types of lakes (Henderson-Sellers, Markland, 1990), which are not listed or considered.

2. Main sources of nutrients entering lakes

Freshwater lakes (reservoirs) contain 0.009% of the world's water reserves and 1.4% of fresh water reserves. In recent centuries, freshwater lakes and reservoirs have been degrading and disappearing at an ever-increasing rate. Human activity and passivity are the main reasons for the rapid degradation of water bodies. Since the 1960s, people's views on their relationship to the natural environment have gradually changed. It is now widely accepted that natural resources are exhaustible and must be protected from overexploitation.

All lakes, according to their state of water, flora and fauna, are divided into several groups: oligotrophic, mesotrophic, eutrophic and others (Odum, 1975; Dreux, 1976; Ricklefs, 1979; Biological Dictionary, 1986; Henderson-Sellers, Markland, 1990; Khristoforova, 1999). But it should be borne in mind that this classification is both subjective and relative, since the category of “trophicity” includes local requirements and reflects the differences in lakes in relatively small regions (Henderson-Sellers, Markland, 1990).

The main problem of lakes is eutrophication. This is an increase in the level of primary production due to an increase in the supply of nutrients, mainly nitrogen and phosphorus. The transition of water bodies from an oligotrophic state through a mesotrophic to eutrophic state is associated with the accumulation of bottom sediments in them and a decrease in the water column, in which, at the same rate of entry of nutrients, their concentration increases. There are natural (lasting for thousands of years and even geological periods) and anthropogenic eutrophication, which can occur very quickly, especially in reservoirs with slow flow.

Essentially, eutrophication is a term for the aging of a lake. The “young” lake is oligotrophic, contains a small amount of nutrients, which is capable of maintaining only a low level of biomass. Natural processes, such as wind erosion or rainwater washout, transport nutrients into the aquatic environment, which supports the development of plants and animals.

The intake of nutrients into a reservoir always exceeds their losses from it, which leads to a “net” accumulation of these substances in the reservoir. The formation of precipitation begins there, usually at an average rate of 0.2–2.0 mm/year or more. As sedimentation progresses, the depth of the lake decreases and root (littoral) vegetation begins to invade previously open areas of the water surface. The lake goes through a middle stage - it becomes mesotrophic and eventually becomes an "old" body of water, which is called eutrophic. In a geological sense, such a lake will soon disappear.
In flowing (rivers, streams) and low-flowing water bodies with slow flow (lakes, reservoirs, ponds, inland seas), the rate of entry of nutrients can exceed the rate of their decomposition as a result of additional anthropogenic input, leading to eutrophication and an increase in biomass.

Most of the nutrients enter the lake with surface and underground runoff (rivers, streams, springs, etc.), and the rest directly with precipitation and the fallout of various particles from the atmosphere. Therefore, it is important to understand the interactions between water and nutrients in watersheds. The availability of nutrients in lakes and their consumption are regulated by certain hydrological processes, as well as biological factors (Odum, 1975; Dreux, 1976; Ricklefs, 1979; Dictionary of Biology, 1986; Henderson-Sellers and Markland, 1990; Khristoforova, 1999).

In an ecosystem limited in phosphorus, a decrease in its concentration leads to limited growth of plants and algae. Under such conditions, the eutrophication process slows down and even becomes reversible.

Nitrogen-limited systems often pose a greater problem than phosphorus-limited water bodies because sources of this nutrient are more difficult to control.
The presence of silicon in the water of lakes is of particular interest, since it is necessary for the development of diatoms, the population of which, as a rule, reaches its maximum in the spring. When the amount of silicon is depleted, a rapid decline or “death” of the diatom population occurs. Silicon dioxide is essential for the construction of diatom shells. In the summer, after the diatoms die off, silicon slowly passes back into the water, although a certain part of it is buried in bottom silt.

The redox cycle of iron is an essential component of the biochemistry of lakes, as it is associated with the redox potential (redox potential) and pH of the aquatic environment.
Manganese is a very important biogenic element, but rare, even if it is limiting. Work on the study of the forms of occurrence of manganese identifies two main sources of its supply: with the waters of tributaries into lakes and release from bottom sediments.

Bottom sediments in reservoirs are formed from two main sources: 1 - the introduction of allochthonous matter (external to the lake system) ensures the entry of inorganic particles and some organic substances into the reservoir (rainy weather increases sediment transport and erosion); 2 - “rain” of dead organic matter from the water masses of the lake (this is the second most important contribution to bottom sediments).

In lakes, there is a constant exchange of nutrients between bottom sediments and the adjacent water, which is basically a diffuse process. This process can be enhanced or supplemented by other factors (Henderson-Sellers, Markland, 1990): turbulence (physical disturbances and washout of bottom sediments), bioturbulence (caused by biological forces - the impact of burrowing organisms, worms, fish, birds, etc.), biotic removal (plant growth from bottom sediments), compaction (nutrients are squeezed out through pores with water), redox potential (for example, iron-rich sediments tend to adsorb phosphorus under aerobic conditions and release it under anaerobic conditions) and biological oxidation (decomposition of organic matter). substances by bacteria that transform nutrients into inorganic biologically accessible form).

3. Functioning of the ecosystem of a lake located in the temperate zone

The physical environment, or biotope, together with the species inhabiting it that make up the biocenosis, forms an ecosystem (biogeocenosis). Aquatic systems (rivers, lakes, seas, etc.) are good examples of ecosystems because they have very clear boundaries and are inhabited by aquatic inhabitants that are not able to live on neighboring land. Aquatic systems are very convenient for study because, as a rule, there is a weak exchange between them and land (Odum, 1975; Dreux, 1976; Ricklefs, 1979; Biological Dictionary, 1986; Zenin, Belousova, 1988; Henderson-Sellers, Markland , 1990; Khristoforova, 1999).

Before moving on to the presentation of materials on the feeding and spawning reservoirs of Pacific salmon, let us consider an example of an ecosystem - a lake located in the temperate zone (Dreux, 1976), which includes most lakes in the regions we are considering.

The flora of lake systems includes a number of aquatic plants belonging to different groups of flowering plants, some of which grow on the shore, others in the water. But the main part of the plant mass in the lakes is represented by microscopic algae - diatoms (Bacilariophyta), blue-green (Cyanophyta), green (Chlorophyta), golden (Chrysophyta), dinophyta (Dinophyta), etc. All these plants, thanks to the energy of sunlight, easily penetrate a certain area depth (in different lakes - it may vary), absorb mineral salts and carbon dioxide dissolved in water, and synthesize their own substance from them, grow and reproduce.

All plants: grasses and large algae of the coastal zone, as well as microscopic algae floating in the water column - phytoplankton, and growing in illuminated areas of the bottom - microphytobenthos, are collectively called primary producers. They produce the vast majority of organic matter in water bodies. Only plants, of everything contained or living in aquatic systems, create organic matter at the expense of inorganic matter with the participation of solar energy. In general, the mass of microscopic algae suspended in water approximately corresponds to the total concentration of salts dissolved in water, which reaches a maximum in spring and autumn (Odum, 1975; Dreux, 1976; Ricklefs, 1979; Biological Dictionary, 1986; Henderson-Sellers, Markland, 1990; Khristoforova, 1999).

Nutrients are components that primary producers utilize for life and reproduction. Algae growth relies on the consumption of at least 19 nutrients, although most are required in trace amounts.

In addition to the three main vital components (carbon, hydrogen and oxygen), primary producers require other nutrients in relatively large quantities. Among them are macroelements (sodium, calcium, phosphorus, magnesium, silicon, nitrogen, phosphorus and sulfur).

The remaining elements are required in smaller quantities and are called trace elements (copper, iron, zinc, chlorine, boron, molybdenum, cobalt, vanadium, manganese). The lack of any of these elements limits the development of primary producers. In most aquatic systems, such limiting nutrients are phosphorus; or, to a lesser extent, nitrogen (Odum, 1975; Dreux, 1976; Ricklefs, 1979; Biological Dictionary, 1986; Henderson-Sellers, Markland, 1990; Khristoforova, 1999).

Many animals feed on phytoplankton, most often small ones, incapable of large and fast movements. They, like phytoplankton organisms, are not able to withstand transport by currents. Collectively, small animals in lakes form zooplankton. These are mainly copepods (Copepoda) and cladocera (Cladocera) crustaceans, protocavity worms - rotifers (Rotatoria); this also includes small larvae of a number of insect species, such as mosquitoes.

It should be noted that certain species of fish also use phytoplankton as food. Animals that feed on phytoplankton are primary consumers because they use ready-made organic matter, limiting themselves to its transformation; but they are not capable of creating organic matter anew.

The smallest of the primary consumers (Copepoda, Cladocera and Rotatoria, etc.) appear in huge quantities, usually when there is a lot of food; therefore, in their development they completely follow the development of phytoplankton. On the contrary, fish that feed on phytoplankton, but have a significant life expectancy, are able to starve for a long time or change food items. Zooplankton, in turn, serves as food for larger animals (insect larvae, many species of fish, some species of birds). All such carnivorous animals, that is, those that feed on other animals, are called secondary consumers. This shows that living beings belonging to different systematic groups can play the same role in ecosystems - they all belong to the same food, or, as they more often say, trophic level. Trophic levels are interconnected by dependencies consisting of elementary connections in the form of a chain - all of them together form the so-called food chain, the links of which depend on each other: the disappearance of phytoplankton leads to the disappearance of zooplankton, and therefore secondary consumers (figure).

The food chain described above plays a dominant role in lakes. But besides it, there are many other food chains in lakes. For example, on coastal plants, which are half under water, phytophagous insects that feed on leaves live on their above-water parts. Birds, in turn, feed on these insects. The underwater parts of plants are gnawed by aquatic insects and their larvae (for example, water-loving beetles), as well as gastropods such as pond snails and squirrels.

Plant food is far from completely digested by primary consumers. The excrement of the latter also contains many plant organic substances, which are especially easily digestible due to the fact that they are crushed in the digestive canal. They feed on a large number of species, among which isopod crustaceans (commonly called worms) predominate. Having passed through their digestive canal, the remains of organic food become the prey of bacteria, which finally decompose them into mineral salts and carbon dioxide, which are again used by plants. This shows that in nature there are also food chains of destructors that completely decompose organic matter.

The concept of a food chain is convenient for presentation; in some cases it corresponds to actually observed phenomena, but in general it is somewhat simplified. It would be more accurate to talk about a very complex trophic network that unites all species living in lakes and covers all metabolic processes occurring in them.

Thus, a continuous flow of matter and energy constantly permeates the ecosystem. If the ecosystem is stable, then it can be compared to a large pipe, at one end of which mineral salts and solar energy flow, and living matter comes out of the other. The latter can be exploited by external predators, such as humans, who, by catching fish from the lake and eating them, form the last link of the food web. In this case, a person plays the role of a tertiary or quaternary consumer, but let us not lose sight of the fact that when collecting watercress on the shores of a lake, following the example of many other organisms, he can also be a primary consumer (Dreux, 1976).

In sockeye lakes, the main source of “new” organic matter is phytoplankton.

Literature

Bugaev V.F., Kirichenko V.E. 2008. Feeding and spawning lakes of Asian sockeye salmon (including some other reservoirs of the range) // Petropavlovsk-Kamchatsky: Kamchatpress Publishing House. - 280 s.

In the photo: colonial algae - Sphaeronostoc priniforme. In Kamchatka it is known from lake. Nalychevo and shallow lakes in the river basin. Right Kikhchik (photo by D. Gimelbrant)

Ecosystem refers to the key concepts of ecology. The word itself stands for "ecological system". The term was proposed by ecologist A. Tansley in 1935. An ecosystem combines several concepts:

• Biocenosis - a community of living organisms
• Biotope is the habitat of these organisms
• Types of connections between organisms in a given habitat
• The metabolism that occurs between these organisms in a given biotope.

That is, in essence, an ecosystem is a combination of components of living and inanimate nature, between which energy is exchanged. And thanks to this exchange, it is possible to create the conditions necessary to support life. The basis of any ecosystem on our planet is the energy of sunlight.

To classify ecosystems, scientists chose one characteristic - habitat. This makes it more convenient to distinguish individual ecosystems, since it is the area that determines the climatic, bioenergetic and biological characteristics. Let's consider the types of ecosystems.

Natural ecosystems are formed on earth spontaneously, with the participation of natural forces. For example, natural lakes, rivers, deserts, mountains, forests, etc.

Agroecosystems is one of the types of artificial ecosystems created by man. They are distinguished by weak connections between components, a smaller species composition of organisms, and artificial interchange, but at the same time, it is agroecosystems that are the most productive. People create them for the sake of obtaining agricultural products. Examples of agroecosystems: arable lands, pastures, gardens, vegetable gardens, fields, planted forests, artificial ponds...

Forest ecosystems are communities of living organisms that live in trees. On our planet, a third of the land is occupied by forests. Almost half of them are tropical. The rest are coniferous, deciduous, mixed, broad-leaved.

In the structure of the forest ecosystem, separate tiers are distinguished. Depending on the height of the tier, the composition of living organisms changes.

The main thing in a forest ecosystem is plants, and the main one is one (less often several) plant species. All other living organisms are either consumers or destroyers, one way or another influencing the metabolism and energy...

Plants and animals are only an integral part of any ecosystem. Thus, animals are the most important natural resource, without which the existence of an ecosystem is impossible. They are more mobile than plants. And, despite the fact that fauna is inferior to flora in terms of species diversity, it is animals that ensure the stability of the ecosystem, actively participating in the metabolism and energy.

At the same time, all animals form the genetic fund of the planet, living only in those ecological niches where all conditions for survival and reproduction are created for them.

Plants are a fundamental factor for the existence of any ecosystem. They are most often decomposers - that is, organisms that process solar energy. And the sun, as noted above, is the basis for the existence of life forms on Earth.

If we consider representatives of flora and fauna separately, then each animal and plant represents a microecosystem at one or another stage of existence. For example, the trunk of a tree as it develops is one integral ecosystem. The trunk of a fallen tree is a different ecosystem. It’s the same with animals: an embryo in the reproductive stage can be considered a microecosystem...

Aquatic ecosystems are systems adapted to life in water. It is water that determines the uniqueness of the community of living organisms that live in it. The diversity of animal and plant species, the condition, and stability of the aquatic ecosystem depend on five factors:

• Water salinity
• The percentage of oxygen it contains
• Transparency of water in a reservoir
• Water temperatures
• Availability of nutrients.

It is customary to divide all aquatic ecosystems into two large classes: freshwater and marine. Marine waters occupy more than 70% of the earth's surface. These are oceans, seas, salt lakes. There is less freshwater: most of the rivers, lakes, swamps, ponds and other smaller bodies of water...

The stability of an ecosystem is the ability of a given system to withstand changes in external factors and maintain its structure.

In ecology, it is customary to distinguish two types of ES sustainability:

• Resistant is a type of sustainability in which an ecosystem is able to maintain its structure and functionality unchanged, despite changes in external conditions.
• Elastic— this type of sustainability is inherent in those ecosystems that can restore their structure after changing conditions or even after destruction. For example, when a forest recovers after a fire, they speak specifically about the elastic stability of the ecosystem.
  Human ecosystem

In the human ecosystem, humans will be the dominant species. It is more convenient to divide such ecosystems into areas:

An ecosystem is a stable system of components of living and non-living origin, in which both objects of inanimate nature and objects of living nature participate: plants, animals and humans. Every person, regardless of place of birth and residence (be it a noisy metropolis or a village, an island or a large land, etc.) is part of an ecosystem....

Currently, human influence on any ecosystem is felt everywhere. For their own purposes, man either destroys or improves the ecosystems of our planet.

Thus, wasteful treatment of land, deforestation, and drainage of swamps are considered to be the destructive effects of humans. Conversely, the creation of nature reserves and the restoration of animal populations contribute to the restoration of the Earth’s ecological balance and is a creative influence of humans on ecosystems...

The main difference between such ecosystems is the method of their formation.

Natural, or natural ecosystems are created with the participation of natural forces. A person either has no influence on them at all, or there is an influence, but it is insignificant. The largest natural ecosystem is our planet.

Artificial ecosystems are also called anthropogenic. They are created by man for the sake of obtaining “benefits” in the form of food, clean air, and other products necessary for survival. Examples: garden, vegetable garden, farm, reservoir, greenhouse, aquarium. Even a spaceship can be considered an example of a man-made ecosystem.

The main differences between artificial ecosystems and natural ones.

Shows a clear unity of structure and function. A body of water can be simply described as: stream, river, river, puddle, pond, lake, sea. And it’s more difficult – as an ecosystem.

Main components of the ecosystem

I've come to the conclusion

that just as a frog is considered a classic object for studying an animal organism, a pond is an example for the initial study of an ecosystem... Without overloading the novice researcher with a large number of details in a pond, four can be collected for study main components of the ecosystem.

1. First of all, these are nonliving substances - the main components of the environment, its inorganic and organic components.
2. Then producers, mainly terrestrial plants, which extract various substances from the inanimate environment under the influence of solar energy and create, produce a mass of living matter.
3. Next come all the other living beings who live either by consuming masses of green plants or by devouring other animals.
4. And finally, fungi and bacteria, which exist at the expense of dead tissues of animals and plants: they process and decompose these tissues into simple substances, which are again used by plants.

Ecosystem

Pond as an ecosystem

1. all elements of this reservoir are closely linked and interact, disruption of the action of one of the elements causes a disruption in the structure and life of the entire pond;
2. the system is in some equilibrium, homeostasis and is capable of restoring this balance if the intervention only disturbs this balance and does not destroy the connections themselves or cause an ecological catastrophe of the system;
3. like a living organism, the system lives, it appears, develops, progresses, reaches its peak, then experiences decline, regression and death (example: temporary reservoirs that form when snow melts, during floods and usually dry up and die in the summer).

Assessment of the condition of the reservoir

1. Anthropogenic pressure on any of the system components. Let’s say that intensive recreational fishing is carried out in a closed reservoir, exceeding the permissible level of exploitation. To maintain a fish stock, it is necessary to periodically introduce and introduce juvenile fish into the reservoir. Another example: the density of fish stocking in a reservoir during stocking turned out to be so high that they do not have enough food. It is necessary to bring in food from outside and feed the fish.
2. The anthropogenic pressure on the entire system as a whole is so strong that equilibrium is not restored. Example: washing cars, motorcycles or other vehicles in ponds (everyone knows about the dangers of the film of petroleum products left on the surface of the water). Or intensive use of the reservoir by owners of motor boats.
3. “Age” and stage of development of the reservoir. In particular, you need to look at the condition of the water and the fish in it. It happens that several days pass from the registration of reservoirs to the deployment of an operation to rescue fry from them. So, when counting, you need to see whether the fry will survive these few days, maybe the water is so bad, the fish are suffocating, and the entire reservoir is close to death, that the operation to save the fry cannot be postponed.

A reservoir as an ecosystem – its biogeocenosis

Relationships between neighboring species in a body of water

Reservoir assessment

Fish ponds

Biocenosis of the reservoir

Reservoir survey

• First of all, the type of reservoir - river, river, lake, lake;
• size of the reservoir;
• movement of water – flowing, semi-flowing, standing.

• Along with speed, it takes into account smoothness of flow: with a large slope, river water can rush at a higher speed, but in northern rivers it is usually a smooth fast current, and in the south in mountainous areas the river speed is often higher, the water forms breakers and whirlpools among the stones. In closed lakes, the mobility of water depends on the nature of the shores: with open shores, the wind blows freely, forming waves and mixing the water mass; in forest lakes, the water surface rarely wrinkles from the wind and the water is weakly mixed, the lower layers can be much colder and may be poor in oxygen. This means that the characteristics of a reservoir include a description of its shores. The dimensions (length, width) and depth of the reservoir are determined.
• Information about greatest depth in the characteristics of the reservoir should be combined with information about smaller bays and well-warmed shallows. Determine water transparency, color, taste.
• Water samples for acidity delivered to the laboratory for analysis. Using these samples, it is possible to determine the sources of water pollution and send signals to the sanitary-epidemiological station.
• It is not always easy to prevent water pollution. Play a big role in maintaining clean water origins rivers and streams feeding reservoirs. Sometimes these springs are polluted, the banks are trampled, and garbage gets into the water. It is necessary to clean the springs, install benches near them, build bridges from which you can draw water without destroying the banks. The bottom of the springs must be cleared of debris, silt, and snags. All discovered springs are numbered and entered into the characteristics of the main reservoir; if possible, their location is plotted on a map or topographical diagram. There are general requirements for the composition in reservoirs. When assessing the oxygen content in water in the field, if the water is not very polluted, you can proceed from average values.

An ecosystem whose natural habitat is water is called an aquatic ecosystem. It is this that determines the uniqueness of a particular ecosystem, species diversity and its sustainability.

The main factors that influence the aquatic ecosystem:

1. Water temperature
2. Its chemical composition
3. Amount of salts in water
4. Water clarity
5. Oxygen concentration in water
6. Availability of nutrients.

The components of an aquatic ecosystem are divided into two types: abiotic (water, light, pressure, temperature, soil composition, water composition) and biotic. Biotics, in turn, is divided into the following subspecies:

Producers are organisms that produce organic substances using sun, water and energy. In aquatic ecosystems, the producers are algae, in shallow water bodies - coastal plants.

Decomposers are organisms that consume organic matter. These are various types of marine animals, birds, fish, and amphibians.

Main types of aquatic ecosystems

In ecology, aquatic ecosystems are usually divided into freshwater and marine. This division is based on the salinity of the water. If a liter of water contains more than 35% salts, these are marine ecosystems.

Marine areas include oceans, seas, and salt lakes. Freshwater - rivers, lakes, swamps, ponds.

Another classification of aquatic ecosystems is based on such a feature as the conditions of creation. Here we distinguish between natural and artificial. Natural ones were created with the participation of the forces of nature: seas, lakes, rivers, swamps. Artificial aquatic ecosystems are created by humans: artificial ponds, reservoirs, dams, canals, water farms.

Natural aquatic ecosystems

Freshwater ecosystems

Freshwater ecosystems- these are rivers, lakes, swamps, ponds. All of them occupy only 0.8% of the surface of our planet. Although more than 40% of fish known to science live in fresh water bodies, freshwater ecosystems are still significantly inferior in species diversity to marine ones.

The main criterion for distinguishing freshwater bodies of water is the speed of water flow. In this regard, standing and flowing ones are distinguished. Standing swamps include swamps, lakes and ponds. Flowing ones include rivers and streams.
Standing aquatic ecosystems are characterized by a pronounced distribution of biotic organisms depending on the water layer:

In the upper layer (littoral) the main component is plankton and coastal thickets of plants. This is the kingdom of insects, larvae, turtles, amphibians, waterfowl, and mammals live here. The upper layer of reservoirs is a hunting ground for herons, cranes, flamingos, crocodiles, and snakes.

The middle layer of the reservoir is called profundal. It receives much less sunlight, and the food is supplied by substances that settle in the upper layer of water. Predatory fish live here.

The bottom layer of water is called benthal. The composition of the soil and silt plays a huge role. This is the habitat of bottom fish, larvae, mollusks, and crustaceans.

Marine ecosystems

The biggest marine ecosystem is the World Ocean. It is divided into smaller ones: oceans, seas, salt lakes. All of them occupy over 70% of the surface of our planet and are the most important component of the Earth's hydrosphere.

In marine ecosystems, the main component producing oxygen and nutrients is phytoplankton. It forms in the upper layer of water and, under the influence of solar energy, produces nutrients, which then settle into the deeper layers of the reservoir and serve as food for other organisms.

Large marine ecosystems are the oceans. In the open ocean, species diversity is low compared to coastal zones. The bulk of living organisms are concentrated at depths of up to 100 meters: these are various types of fish, mollusks, corals, and mammals. In coastal zones of marine ecosystems, species diversity is supplemented by numerous species of marine animals, amphibians, and birds.

In the coastal zones of marine ecosystems, smaller ones (by territory) are distinguished: mangrove swamps, shelves, estuaries, lagoons, salt marshes, coral reefs.

Places on the coast where sea water mixes with fresh water (river mouths) are called estuaries. Species diversity reaches its maximum here.

All marine ecosystems are very resilient, able to resist human intervention and quickly recover from anthropogenic influence.

Artificial aquatic ecosystems

All artificial aquatic ecosystems are created by man to satisfy his own needs. These are various ponds, canals, creeks, and reservoirs. Smaller ones include oceanariums and aquariums.

Artificial aquatic ecosystems are characterized by the following features:

• Few plant and animal species
• Strong dependence on human activity
• The instability of an ecosystem, since its viability depends on human influence.

Lakes arose on Earth as a result of tectonic shifts in rock, retreat of glaciers during melting, or changes in river beds. These include ponds and smaller water formations. What they have in common is that they are closed ecosystems with a tendency to disappear.

It doesn’t matter whether the reservoir is wastewater, that is, from which water flows, or without drainage, the ecosystem of the lake will gradually transform towards the predominance of flora over fauna. Then turn into a swamp and eventually dry up and disappear. The speed of such transformation depends only on the size and depth of the water body.

System structure and main influencing factors

The ecosystem of a lake is a collection of species that exists within the boundaries of a water body and interacts with each other. The trophic chain is typical and consists of producers - plants and algae, consumers - fish, reptiles, waterfowl, some species of animals, as well as reducers - bacteria, worms and crustaceans.

Schematic illustration of a lake ecosystem.

Whether the water in a lake is salty or fresh only affects the species structure, which is dominated by living organisms adapted to existence in water with more or less salt content.

The main and defining one is the sun. When interacting with water, solar energy changes, namely increases, the temperature of the latter. This, in turn, affects the process of photosynthesis, that is, the production of oxygen, its content and solubility in water.

Based on the amount of incoming solar energy, the water mass of the lake can be divided into horizontal layers or strata.

In summer, the top layer receives the maximum amount of solar energy. It's heating up. Producers actively convert solar energy into oxygen. The fauna in the upper layer plays the role of consumers. These are mainly waterfowl and birds, reptiles, some types of fish and insects.

The next layer of water plays a “barrier” function between different temperature layers located above and below it. This layer has the maximum density of water, which occurs when its temperature is +4°C. It inhibits the mixing of the lake's water layers. Mixing usually occurs in spring and autumn. As a result, oxygen and nutrients are exchanged.

Sunlight, reaching the bottom layer, is highly scattered. The remains of living organisms and their waste products fall to the bottom. The bottom layer is inhabited by decomposers - crayfish, worms, insect larvae, bacteria and microorganisms. Very rare fish. Their main function is the processing of organic waste. The last stage of the food chain, before a new one begins.

At this stage, the failure occurs, which ultimately leads to the disappearance of the lake. Living conditions do not allow us to cope with waste recycling completely. And the top layer, fed during mixing, increases the biomass. Waste increases and residues accumulate. They turn into silt and then into peat. The lake begins to shallow and disappear.

Human use

The use of the lake by humans can be described very briefly. Man takes water and food from it, and returns untreated water and waste.

Before completely disappearing, the lake turns into a swamp. Bottom silt becomes peat. Peat has the ability to retain moisture. Accumulating it during the period of melting snow or rain, it then gives it to streams and thereby maintains the water level in large reservoirs and groundwater. Man, by extracting peat as a natural fuel or fertilizer, carrying out reclamation work and draining swamps, changes the water regime of the region with all the ensuing consequences.

The lake ecosystem does not contain phosphorus, nitrogen and other substances that stimulate plant growth. Wastewater from industrial enterprises, discharges from city sewer systems, untreated domestic wastewater and, most importantly, water drained from lands used for agricultural needs after rainfall and snowmelt contain these substances. And they accelerate growth and increase the amount of biomass, especially blue-green algae.

The same effect occurs when warm water is discharged after cooling power plant equipment with it. An increase in water temperature as a result of such discharges accelerates the growth of the same algae and other plants. If the temperature is too high, the animal world may die altogether or a malfunction in its reproductive system may occur.

But the most important thing is that the rhythm of spring and autumn mixing of waters is disrupted, as a result of which the bottom layers will not receive the necessary supply of oxygen.

Another form of human use of the lake ecosystem is the introduction of living organisms into it that are unusual for it. Sometimes this can happen by accident. But it happens that this is done deliberately, with the aim of breeding species of fish, shellfish, invertebrates and the like that are useful to humans.

These organisms behave aggressively towards local species of flora and fauna. And taking into account the stimulation of their growth and development by humans, the natural biosystem begins to undergo significant changes. An imbalance occurs that can lead to its complete death. An example is the Great Lakes in America.

You will be interested to see photos and pictures of the lake’s ecosystem.

Watch the video: Beautiful photos of lakes, rivers and seas.