LAKE
body of water surrounded by land. Lakes vary in size from very large, such as Caspian Sea and the Great Lakes North America, to tiny reservoirs of several hundred square meters or even less. The water in them can be fresh, as in the lake. Upper, or salty, as in the Dead Sea. Lakes are found at any height, from the lowest absolute mark on Earth on the land surface -408 m (Dead Sea) and almost to the highest (in the Himalayas). Some lakes do not freeze all year round, while others, such as Lake. Vanda in Antarctica, ice-bound for most of the year. Many lakes exist permanently, while others (for example, Lake Eyre in Australia) are only occasionally filled with water. Despite their diversity, lakes of all types share a number of common physical, chemical and biological characteristics and are subject to many general laws. Therefore, the study of lakes in all their diversity and in all aspects is dealt with by one scientific discipline - lake science, or limnology (from the Greek lmn - lake, pond and logos - word, doctrine). Probably the best way to understand the nature of lakes is to consider them not only as landforms but also as aquatic ecosystems in which the interaction of all components leads to the establishment of observable conditions and where a change in one characteristic causes more or less significant changes in all other components of the ecosystem. In this sense, lakes are similar to oceans, but there are differences between them: lakes are smaller and more vulnerable to external influences, including natural climatic changes. Age is one of the significant differences between lakes and oceans. Only a few of the existing lakes, such as Tanganyika or Baikal, are several million years old. Most of the lakes are probably younger than 12,000 years, and man-made lakes - artificial reservoirs - are only a few decades old.

EAST COAST OF LAKE TANGANIK, confined to the East African Rift Zone.

ORIGIN OF THE LAKE BELLS
The lakes fill basins that have different genesis. Since the formation of these basins is often dependent on local conditions, lakes are concentrated in certain areas, such as the Lake District in northwest England, the lake district in Austria, and the vast belt of lakes that covers the states of Minnesota, Wisconsin and Michigan. The formation of lake basins is influenced by tectonic activity, volcanism, landslides, glacial processes, karst and suffusion, fluvial processes, eolian processes, coastal processes, accumulation of organogenic deposits, damming of watercourses by humans or beavers, and meteorite fall. The oldest and deepest of the existing lakes arose under the influence of tectonic activity, but most of the lakes were formed due to glacial processes. Nevertheless, the role of other listed factors is also important.
Tectonic activity. Tectonic depressions arise as a result of movements of the earth's crust, and many lake basins of tectonic origin occupy large area and are ancient. They are usually very deep. Tectonic processes manifest themselves in different ways. For example, the Caspian Sea is confined to a deflection at the bottom ancient sea Tethys. In the Neogene, an uplift occurred, as a result of which the Caspian depression became isolated. Its waters gradually desalinated under the influence of atmospheric precipitation and river runoff. The basin of the lake Victoria in East Africa formed as a result of the dome uplift of the surrounding land. The Great Salt Lake in Utah also arose due to the tectonic uplift of the area through which the flow from the lake was previously carried out. Tectonic activity often leads to the formation of faults (cracks in the earth's crust), which can turn into lake basins if a reverse fault occurs in the area or if a block enclosed between faults sinks. In the latter case, the lacustrine basin is said to be associated with a graben. Several lakes within the East African Rift System have this origin. Among them - lake. Tanganyika, formed ca. 17 million years old and very deep (1470 m). On the continuation of this system to the north are the Dead Sea and Lake Tiberias. Both are very ancient. Max Depth Lake Tiberias is currently only 46 m. ​​The grabens are also confined to Lake Tahoe on the border of the states of California and Nevada in the USA, Biwa (the source of freshwater pearls) in Japan and Baikal, which holds the world's largest mass of fresh water (23 thousand km3), in Siberia.

Volcanic activity leads to the formation of a variety of lake basins - from small rounded craters with low sides (maars) to large deep calderas formed when magma erupts through a side crater located near the top of the volcano, which leads to the collapse of the volcanic cone. A good example of a caldera lake is Lake. Crater in Oregon, formed during the eruption of the Mazama volcano c. 6000 years ago. This picturesque lake of almost round shape has a depth of 608 m (seventh deepest in the world). In the middle of the lake is the island of Wizard, which arose as a result of a later eruption. Lakes of this type are found in Japan and the Philippines. In volcanic areas, lake basins can also form when hot lava flows from below a colder surface lava horizon, which contributes to the subsidence of the latter (this is how Yellowstone Lake was formed), or when rivers and streams are dammed by lava or mud lava flow during volcanic eruptions. This is how the basins of many lakes in Japan and New Zealand arose.

Landslides, podruzhivaya water flows, contribute to the formation of lakes. However, if the dam collapses or water overflows, these lakes soon disappear. For example, in 1841, the Indus River in the territory of modern Pakistan was dammed by a landslide resulting from an earthquake, and six months later the "dam" collapsed, and the lake, 64 km long and 300 m deep, was lowered in 24 hours. A lake of this type can only remain stable if excess water is drained through erosion-resistant hard rock. For example, Lake Sarez, formed in the Eastern Pamirs in 1911, still exists and has a depth of 500 m (the tenth deepest lake in the world). Glacial activity is the most effective factor in the creation of lake basins. Ice sheets several kilometers thick, which in geologically recent times covered much of North America and much of northern Europe, formed lake basins in various ways, and most of the lakes in these regions are of glacial origin. For example, many lakes are confined to plowing basins, which were formed during the movement of glaciers over a heterogeneous surface. At the same time, glaciers demolished loose sediments. Thousands of lakes that have filled such basins are found in northern Canada, Norway and Finland, where they occupy significant areas.

Karovye lakes are located on the slopes of the mountains in the upper reaches of the troughs. They are characterized by hollows, shaped like amphitheatres. Frost weathering processes also take part in the formation of the beds of such lakes. Fjord lakes have an elongated shape, steep banks and a U-shaped transverse profile. They occupy depressions at the bottom of river valleys, reworked and deepened by large glaciers. Good examples of lakes of this type are Loch Ness in Scotland and many lakes in Norway. Partly by glacial processes, a group of lakes has been formed, radiating from a single center in the Lake District in northwest England. The large lakes of northern Canada - Athabasca, Great Bear and Great Slave - have a similar origin. The depth of the latter reaches 640 m. Even the basins of the Great Lakes, which have a complex genesis, have been affected by glaciers. In addition, lakes are formed when river valleys are dammed by moraines. Finally, during the retreat of the glaciers, huge blocks of dead ice. Many of them melted only hundreds of years later, when the climate improved, and basins filled with water appeared in their place.
See also GLACIERS.

Karst and suffusion. Karst lakes are formed when soluble minerals and rocks such as limestone, gypsum and rock salt are carried away by water, either depressions on the surface or underground voids are formed, the roof of which then collapses. These lakes are not necessarily small: for example, Lake. Zhirot in french alps has a depth of 99 m with an area of ​​​​only 57 hectares.
fluvial processes. As a result of the activity of rivers, lakes are formed in several ways: water wells appear at the foot of waterfalls; depressions are developed in the rocky soil by flowing waters under the influence of the process of evorsion (when holes are drilled due to the friction of stones and other abrasive material on the bottom in whirlpools); river channels are blocked during the removal of river sediments by other rivers and their accumulation. For example, the Mississippi River formed a lake. St. Croy near St. Paul (Minnesota), having dammed the St. Croy River, but then itself was dammed downstream by sediments of the Chippewa River, and as a result, Lake was formed. Pippin. Finally, in valleys with well-developed floodplains, for example, in the valley of the Mississippi River in the states of Louisiana and Arkansas, as a result of the breakthrough of the necks of meanders and channel processes, oxbow lakes are cut off in the form of large meanders.
eolian processes. In basins of eolian origin, there are lakes dammed by eolian sands or enclosed among dunes. There are also deflationary lakes, confined to blowout basins, which are common in arid or semi-arid regions of Texas, South Africa and Australia. The origin of deflationary lakes, sometimes called playas, is not fully understood, but it is possible that they are sometimes formed by the combined action of wind blowing and excavation by animals that use them for watering.
coastal processes. During the movement of the alongshore sediment flow sea ​​bays can be separated by sand bars and turn into lakes. If such a bar remains stable, the resulting salt Lake then desalinated. Processes of accumulation of organogenic deposits. Lake Okeechobee in Florida is one of the better known lakes formed from such processes. Although its basin arose when a depression was raised at the bottom of the sea, originally Lake. Okeechobee was dammed by dense aquatic vegetation and accumulations of its remnants. Damping of streams by humans or beavers. Dams built by beavers can reach large sizes - more than 650 m long - but they are short-lived. Unintentional human activity has led to the creation of thousands of lakes at the site of quarries and mine workings, and, in addition, dams have been specially built. During the construction of large dams in Africa, huge reservoirs arose, including Nasser on the Nile River, Volta on the Volta River and Kariba on the Zambezi River. Some dams were built to generate electricity for aluminum smelting from large local deposits of bauxite.
impact of meteorites. Probably the most rare and unusual lake basins are depressions formed as a result of meteorite impacts. It has been reliably found out that one of the lakes of the Ungava Peninsula in the prov. Quebec (Canada) is confined to the Nouveau Quebec meteorite crater. This rounded lake is located among lakes of glacial origin, which have an irregular shape.
SOURCES OF LAKE WATER
To be called a lacustrine basin, formed by one of the methods described above, of course, must at least occasionally be filled with water, which can enter the lake in various ways. In many large lakes in humid regions, a significant part of the water can come directly from atmospheric precipitation falling on the surface of the lakes. For example, food Victoria in East Africa is about 75% atmospheric. The main source of water for smaller lakes or lakes in more arid areas is usually the surface runoff of rivers and streams. Lakes can be fed by groundwater that comes out in the underwater part of the lake basin. Many lakes, in particular of glacial origin, are associated with hollows worked out in the strata of loose aquifers and are located below the groundwater level. In this case, water enters the lake or flows out of it, seeping through the sides of the basin. There are also key lakes, at least partially fed by underwater springs. Sometimes, from sources, a huge amount of salts enters the lake, captured during the passage of a watercourse through easily soluble rocks (for example, in Lake Tiberias). The freshest waters are characteristic of lakes fed exclusively by atmospheric precipitation. However, the salinity of lakes also depends on how the water leaves the lake. The content of mineral salts in flowing lakes is usually close to their concentration in the feed stream. Lakes, in the basins of which water is filtered both into and out of the lake, are usually fresh. However, some lakes have an inflow of water, but no runoff, and water only evaporates from their surface, resulting in an increase in the concentration of soluble salts in water bodies. In such endorheic, or "closed" lakes (as opposed to "open"), highly specialized communities of plants and animals, such as some crustaceans or insects, often form. Another factor affecting the salinity of lakes is the amount of precipitation. Finally, the nature of the rocks among which the lakes are located is of great importance. Thus, the lakes in the area of ​​the Canadian Shield are mostly very fresh, since the rocks through which the water flows are completely insoluble. An essential aspect of the water balance of lakes is the rate of water exchange. This characteristic is determined either by the time of complete water change in the lake (in years), which is expressed through the ratio of the volume of the lake to the annual water flow from it, or through the inverse value, called the water exchange coefficient of the reservoir. The time for a complete water change can be very short - one week or less, which corresponds to a water exchange coefficient of 50 times a year - for reservoirs located on rivers above dams, but it can also be long - up to 500 years, with an annual water exchange coefficient of 0.002 (as in Lake Superior). Water bodies with a shorter cycle of complete water change (and, accordingly, with high water exchange coefficients) are cleared of pollutants faster and generally have lower concentrations.
SUBSTANCES DISSOLVED IN LAKE WATER
Water is an excellent solvent, and therefore lake waters contain a lot of dissolved substances. It is noteworthy, however, that the vast majority of these substances in most lakes are represented by a limited number of compounds, namely, positively charged ions (cations) of calcium, magnesium, sodium and potassium and negatively charged ions (anions) consisting of carbon and oxygen (bicarbonates), sulfur and oxygen (sulfates) and chlorine (chlorides) (both groups of ions are listed in descending order of their content). These seven ions make up 90 to 95% total dissolved substances in the waters of most lakes, and their total concentration, usually measured in milligrams per liter (mg / l), characterizes the salinity (mineralization) of the water. Other substances, such as plant nutrients (nitrogen and phosphorus) and metals (iron and manganese), are present in much lower amounts, so that their concentrations are measured in micrograms per liter (µg/L). In drainless lakes, evaporation leads to a change in the composition of salts. Lakes are called chloride, sulfate or carbonate lakes, depending on which anions have accumulated in them. most under the influence of evaporation or atmospheric precipitation.

STRATIFICATION OF LAKE WATER
In some lakes, especially in shallow waters or those exposed to strong winds, there is no noticeable water stratification at all. This means that the water masses are more or less constantly mixed by the action of the wind and are fairly homogeneous in all respects. However, for most deep lakes and those that are in the wind shadow, a distinct stratification of the water column according to physical properties is characteristic, as a result of which less dense waters are located above denser ones. Such stratification significantly affects the chemical composition and biology of lakes.

When solar energy interacts with water, the latter acquires a unique property: its density reaches its maximum value (1.0) at a temperature of approx. 4 ° C, gradually decreasing both with increasing and decreasing temperatures. In lakes, sunlight is used by plants for photosynthesis and by animals to see underwater. Light also influences the vertical migrations of some organisms, but the main effect of solar energy is water heating. The influx of energy from the Sun is significant. The arrival of solar energy during one summer day can reach 500 cal per 1 cm2 of the lake surface. Part of this energy is reflected from the mirror of the lake, part is scattered by the water surface into space, and part is absorbed by water and converted into thermal energy. This thermal energy is partially radiated back into the atmosphere or spent on evaporation. It is mainly the upper layer of water several meters thick that is heated, since the radiation is quickly absorbed as it penetrates deeper. Heating causes the water in this upper layer to expand, causing its density to decrease compared to that of the underlying cold layers. Heated water accumulates on top of cold and therefore denser waters. However in early spring , especially in temperate regions, the temperature of the water as a whole remains low, so that the decrease in density due to such heating is insignificant, and the wind mixes the heated water throughout its thickness. Later, as the influx of solar energy increases, the water temperature in the lake as a whole rises, and the decrease in density per unit temperature increment becomes greater, as well as the volume of the heated near-surface water layer. Ultimately, the wind is no longer able to mix the entire water mass, and the influx of solar energy is concentrated in a few upper meters of water. As a result, the lake waters are divided into two horizons: the upper, less dense, warm - epilimnion, and the lower, denser, cold - hypolimnion. The intermediate layer, in which there is a rapid decrease in temperature with depth, is called the metalimnion, or thermocline. Such stratification is determined more by the density of water than by its temperature. Because in tropical regions, where water temperatures are generally higher, density changes are much greater (see graph), and the temperature difference between epilimnion and hypolimnion can be much smaller than in temperate areas. In any case, if the density of water in the epilimnion and hypolimnion differ by 0.001 to 0.003, a noticeable stable stratification is achieved. Such small differences allow lake waters to resist mixing even under the influence of strong winds. At the end of summer, when the days become shorter and the influx of solar radiation decreases, the upper layer of water cools down, becomes denser and soon, together with the underlying waters, undergoes wind mixing, due to which the power of the epilimnion increases. This process continues until the temperature of the water throughout the entire depth of the lake, as a result of mixing, equals the temperature of the hypolimnion or becomes close to it. In tropical regions, where temperatures are consistently above 0°C, this kind of circulation of lake waters can continue throughout the winter. However, where winter air temperatures drop below 0 ° C, lake waters continue to cool and mix until a temperature of 4 ° C is established. If further surface waters cool below this temperature, corresponding to the maximum density of water, they again become lighter and remain on the surface, creating a stratification in the lake, which not only depends on density, but is also inversely related to temperature. Ice binding of the water surface has a stabilizing effect, and such stratification persists throughout the winter, until complete mixing of lake waters occurs again in spring. Thus, periods of summer and winter stratification and spring and autumn mixing of lake waters are usually distinguished in the annual cycle of lakes. In most lakes, depending on the climatic features of the region, stratification is established once or twice a year, or is not established at all for a more or less noticeable period. However, the stratification of other lakes persists, usually due to the fact that the density of deep waters increases not due to temperature differences, but rather due to a higher concentration of dissolved chemical compounds. Such lakes, in contrast to periodically completely mixed ones, are called partially mixed lakes, since mixing does not occur in the lower layer. The same layer can exist in very deep lakes, such as Tanganyika, where the seasonal dynamics of air temperatures proceeds so quickly that the water in the lake does not have time to completely mix. The ability of lakes to store heat during the summer and release it in the winter can have a significant moderating effect on the local climate. This is especially true for large lakes such as the Great. For example, oz. Michigan annually absorbs and then gives off more than 50 kcal of heat per 1 cm2 of its surface.
HYDRODYNAMICS OF LAKES
The movement of water in lakes differs significantly from high-amplitude tidal and powerful ocean currents. Only in such large lakes as Superior and Michigan, there are constant currents, but even in them there are practically no tidal fluctuations (their amplitude in Lake Superior is only 3 cm). Nevertheless, under the influence of the temperature gradient, flowing streams and winds, water moves in the lakes. For example, at the end of summer, when heat is released from the surface of the lakes into the atmosphere at night, the water, cooling in this way, becomes heavier and sinks towards the hypolimnion, mixing with its upper layer. This is one of the main mechanisms of epilimnion growth in depth, which leads to complete mixing of water in autumn. When a river flows into a stratified lake, a runoff current occurs either in the surface layer or at medium depths. Surface currents are formed when the tributary waters have a lower density than the waters of the lake itself, as, for example, in summer when the Jordan River flows into Lake Tiberias. Medium-depth currents are formed if the watercourse rushes down to the layers corresponding to its own density. If water flows through the dam at the same time, this current can spread over long distances and carry waters with specific properties (for example, with a higher or lower silt content) through the entire reservoir. If the density of the watercourse is higher than the density of any layer of lake water, it will sink to the bottom and form a bottom current. In this case, even the formation of an underwater channel is possible, as, for example, at the confluence of the river. Rhone in Lake Geneva . Under the influence of wind, several types of movements of lake waters arise. One of them - the eddy wind current (or Langmuir circulation) - is clearly distinguished on the surface of lakes by alternating smooth and small rippled bands. When the wind blows, the water moves with the wind and forms cylindrical eddies whose axes are parallel to both the direction of the wind and the surface of the lake. In some vortices, the movement occurs clockwise, and in others - counterclockwise. As a result, longitudinal (windward-stretched) zones of convergence (oncoming and downward movement of water) are formed, alternating with longitudinal zones of divergence (ascending and divergent movement of water). Divergence zones are located at some distance from one another (for example, from 5 to 15 m). They are easily recognizable as smooth streaks as bubbles, dust and other floating objects collect along convergence zones where water sinks but is not fast enough to carry this material with it. Another type of water movement occurs when the wind constantly blows over the surface of the lake. Since the water moves with the wind, the water level at the far end of the lake rises somewhat, which leads to the formation of a compensatory current - either along the coast, if the lake is shallow, or, in deeper lakes, oppositely directed and passing at some depth from the surface. However, if the wind subsides, as a result of the surge of water to the far shore, a compensatory current forms on the surface of the lake, and the water moves first in one direction, then in the other, until these oscillations die out. Such surface movements of water with variable direction are called surface seiches. On large lakes, their height can exceed several meters. Seiches can cause great damage to low-lying coastal areas. Fortunately, these seiches fade fairly quickly and the lakes return to normal. If the lake is very deep or has a clear stratification, another type of water movement may occur, called inland seiches. When water moves with the wind, its level rises by approximately 1 mm per linear kilometer. If the wind is steady, then the balance of the water mass is disturbed. Both near the surge and surge shores of the lake, warm, less dense water masses are located above the cold and denser ones, but near the surge coast, the water layer is several millimeters larger. To balance the excess pressure created by this additional layer of water, the denser bottom waters move against the wind to the opposite shore of the lake, while the less dense surface waters move downwind. This leads to a distortion of the thermocline: it rises on the leeward side of the lake. However, since the density difference between surface and bottom waters is often only approx. 0.001 of the average density of water, the change in the ratio of these two types of water required to balance the shear exceeds the magnitude of the surge by about 1000 times. Therefore, the thermocline skew is very large compared to the magnitude of the surge: on such large lakes as Baikal, it can reach or exceed 150 m. . As a result, the surface and bottom waters continue to fluctuate, and the thermocline, like a pendulum, changes its inclination to one side or the other, until, finally, this movement dies out, and the lake comes to a state of internal equilibrium. The duration of such fluctuations is determined by the parameters of the lake basin, but it is much longer than the attenuation period of surface seiches, and, for example, on the lake. Baikal can reach 30 days. It is noteworthy that as a result of such oscillatory movements of bottom waters, only slight vertical mixing occurs, but the water is transported over long horizontal distances and may even come into contact with bottom sediments and change its chemical properties. In addition, such movements contribute to the transport of pollutants discharged into the upper part of the bottom water layer at one side of the lake for many kilometers to another place, where water is possibly abstracted for industrial or domestic needs. Under some conditions, inland seiches can even cause deep waters with very low levels of dissolved oxygen to reach the surface of the lake near the shore, where it causes fish to die. Such a phenomenon is periodically observed in Lake Tiberias with a characteristic 24-hour period of internal seiches, coinciding with the daily frequency of summer winds.
LIFE OF THE LAKES
The lakes are home to a wide variety of living organisms, from viruses and bacteria to freshwater seals and sharks. These organisms are not only affected by the physical and chemical properties of their habitat, but also influence it themselves, especially in stratified lakes. There are three types of habitats in lakes: the zone of contact between the atmosphere and water, the zone of contact between bottom sediments and water, and the water column itself. In each zone there is a set of organisms adapted to the specific conditions of a given type of habitat.
The zone of contact between the atmosphere and water. Organisms living in this zone are collectively called "neuston" (from the Greek neusts - floating). Although these organisms are interesting in their own right, the group as a whole is quite small. Its most famous representatives are water strider bugs, swimming beetles and mosquito larvae that hang attached to the surface film of water.
Contact zone of bottom sediments and water. The totality of organisms living in this zone is called benthos (from the Greek. bnthos - depth). This group includes both plants and animals. Plants, commonly known as aquatic, or macrophytes, live in shallow waters where light is available and form a certain zoning. At the bottom, along the edge of the lake, semi-submerged macrophytes grow, including sedges and cattails. Farther from the shore and somewhat deeper, such macrophytes take root, such as, for example, water lilies with long stems topped with floating leaves, through which carbon dioxide from the atmosphere is absorbed. Further away from the coast, greater depth macrophytes (for example, pondweeds) grow completely submerged in water. In North America, this group includes many species, including curly pondweed (Potamogeton scirpus), urut (Myriophyllum exalbescens), and others. Most (though not all) of these plants take root in the bottom soil, from where they extract nutrients. The size of the lake area occupied by such plants depends on a number of factors: on what proportion of the lake area is shallow, on the properties of bottom sediments, and on the characteristics of wave activity. While in some lakes with steep underwater slopes (for example, in the Upper) there are almost no macrophytes, in many lakes of smaller sizes or in large, but shallow ones (for example, in Lake Neusiedler See on the border of Austria and Hungary), the bottom can be completely covered with such plants. In tropical regions, floating aquatic plants are common, for example, eichhornia, or water hyacinth (Eichhornia), and pistia (Pistia), in temperate latitudes - tiny duckweed (Lemna). These plants, especially the larger ones, can grow strongly and form a dense continuous cover on lakes and reservoirs. The vast surface area of ​​shallow water plants serves as a habitat for a group of organisms attached to them called periphyton (from the Greek peri - around, around and phytn - plant), which includes bacteria, protozoa and algae. These organisms make the underwater parts of plants slippery to the touch. Shallow (littoral) areas also give shelter to various animal organisms - gastropods and bivalves, leeches, insect larvae that live among plants and stones that are often found in the coastal zone. Deeper, outside the littoral zone, macrophytes do not grow. The sublittoral zone is located here, where the bottom gradually descends towards the deep part of the lake. Bacteria, protozoa and true worms, as well as larvae similar to them, live in the sublittoral zone. different types insects. With depth, habitat conditions become less favorable (especially in stratified lakes), and only a few adapted species are found there.
Water column. The organisms living here are divided into two groups: nekton and plankton, i.e. small organisms that float in water and are generally incapable of moving against the watercourse. Both terms have Greek roots: nektos - floating and plankton - wandering.
Nekton. According to their nutritional habits, lake fish are divided into several groups. Fish-eating or predatory fish, which are often non-commercial species, feed mainly on smaller fish and fry of other fish species. Planktivorous fish feed on plankton suspended in the water column and are themselves often eaten by predatory fish. Fish that feed on algae and herbivorous fish such as carp that feed on shallow water plants stand out. Benthivorous fish eat animals that live at the bottom of water bodies and organic particles that fall to the bottom of the lake.
Plankton. The term "plankton", originally introduced to refer to organisms (plants and animals) passively swimming in the upper part of the ocean waters, is also used for organisms that live in lakes. There are phytoplankton (plant organisms) and zooplankton (animal organisms). All of them are microscopic and have a specific gravity close to that of fresh water, but if it were higher, the plankton would quickly sink to the bottom.

Blue-green algae: 1 - Oscillatoria, 2 - Microcystis aeruginosa, 3 - Anabaena, 4 - Coelosphaerium, 5 - Spirulina, 6 - Aphanizomenon flos-aquae. Green algae: 7 - Scenedesmus, 8 - Closterium, 9 - Spirogyra, 10 - Staurastrum, 11 - Chlorella, 12 - Micrasterias, 13 - Xanthidium, 14 - Cosmarium, 15 - Pediastrum.

Phytoplankton is represented by microscopic algae, consisting of individual cells or their colonies (sometimes immersed in mucus) or filamentous algae. In fresh water bodies, four functional groups of phytoplankton are distinguished, consisting of representatives of six or seven departments of the plant kingdom. The chloroplasts (specific intracellular formations) of green algae contain the green pigment chlorophyll, which is not masked by other pigments. In diatoms, chlorophyll is accompanied by other pigments that often give them a golden brown color. In blue-green algae, which many biologists consider bacteria (cyanobacteria), chlorophyll is dissolved in the protoplasm of the cell and masked by other pigments, which is why they have a bluish-green color. Pigmented flagellates, capable of actively moving, are a group of small organisms belonging to different departments of the plant kingdom. Although all types of algae are usually present at the same time, the prevalence of one or another of them is seasonal. For example, in temperate regions, diatoms are most abundant in spring, then at the end of spring they are replaced by green algae, in summer - blue-green, and in autumn - diatoms again. In the same climatic conditions in nutrient-rich lakes, blue-green algae dominate most of the year, as is often the case in the tropics. Flagellates, like some blue-green algae, are often present under ice in winter. The reasons for successive changes in algae types throughout the year and the predominance of some of them over others are different. Numerous conflicting theories exist to explain these phenomena. In some lakes, up to 200 species of algae can be simultaneously detected at concentrations reaching hundreds of thousands of cells per 1 ml of water. The spring maximum concentration of diatoms is often called the spring bloom of water bodies, and the autumn maximum, respectively, the autumn bloom. An important property of diatoms is that they use silica (SiO2) to build a hard shell around the cell called a shell. Therefore, diatoms are heavier than other algae. In some blue-green algae, cell buoyancy is regulated by gas vacuoles. Algae play an important role in lakes, as they, together with larger plants, form the first link in the water food chain. In the process of photosynthesis, they, using sunlight captured by chlorophyll and other pigments, extract about 18-20 elements from lake water and use them in building a new cellular substance. At the same time, dissolved oxygen is released in the surface layer of water, where photosynthesis takes place. The energy accumulated in this way in primary production is then used for the life of other organisms living in the lake. Zooplankton are commonly referred to as microscopic animals or other microscopic organisms that do not carry out photosynthesis. Zooplankton includes some groups of bacteria, as well as protozoa, rotifers and tiny crustaceans. Although non-pathogenic (not disease-causing) bacteria are not animals, they are included in zooplankton. They abound in lake water, where their concentration can exceed 100 million in 1 ml. If not for these bacteria (many of which decompose organic matter into its constituent parts), the metabolism in lakes would slow down and eventually stop, since all available minerals would be bound into organic compounds in living or dead organisms. Instead, bacteria convert dead organic matter into free chemical elements and thus complete the cycle, again making these elements available for photosynthesis and growth. Protozoa are microscopic single-celled animals, sometimes called non-cellular, such as amoeba and paramecia (ciliary ciliates). They are often found in abundance in lake waters. Some of them attach themselves to larger organisms, others float freely in the water, feeding on bacteria or the smallest organic residues - detritus. A more complex structure than the simplest, have rotifers, so named for the corolla of hairs, or cilia, around the mouth opening. These cilia vibrate harmoniously in such a way that they give the impression of a spinning wheel. Rotifers are multicellular animals. They feed on small algae, bacteria and organic detritus, and occasionally other rotifers. In most cases, their reproduction is sexual, both females and males participate in it. However, in many cases, parthenogenetic reproduction occurs, in which only females participate. Females lay eggs that carry a diploid set of chromosomes, from which females also develop. Only in harsh environmental conditions do females lay eggs with a haploid set of chromosomes. Some of these eggs then develop (without fertilization) and hatch into males that produce haploid sperm. These males fertilize haploid eggs, and special, so-called. resting (latent) eggs that have increased resistance to harsh conditions, such as drying. When environmental conditions become favorable again, female individuals develop from resting eggs, reproducing parthenogenetically. The smallest crustaceans are one of the most visible constituents of zooplankton. These crustaceans are very small - 0.3-12 mm long. In most lakes, they are the main link between primary producers (algae) and subsequent links in the food chain (fish). They are so small that they feed only on microscopic algae, but they are large enough to be food for fish. Thus, the abundance of these crustaceans is controlled by two factors: food availability and predators. First of all, larger ones are eaten, i.e. more noticeable, crustaceans. In other words, predation is selective. There are two groups of lake crustaceans: copepods and cladocerans. Copepods resemble shrimp in appearance, as they have a clearly defined head, chest and abdomen, ending in a tail. Separate groups copepods are distinguished mainly by the length of the antennules: in some they are very short, in others the length of the antennules exceeds the length of the body. Although some copepods feed on filamentous algae, many of them eat smaller animals. Reproduction is sexual, and approximately the same number of males and females are born. The eggs are carried in a single or double chambered oviduct located at the base of the tail. The eggs develop into larvae that look completely different from adult crustaceans. After six molts, they take on the appearance of adults. Copepods can be recognized by their characteristic spasmodic swimming style. The copepods include the Cyclopes, who, like the mythological namesake, have a single eye in the middle of the "forehead". The body of branched crustaceans is enclosed in a translucent bivalve chitinous carapace (shell). Most cladocerans are herbivores. They filter the water with swimming limbs equipped with feathery bristles, extracting from it the smallest particles of organic detritus, bacteria and especially algae, although some of the cladocerans are predators. Filtered food moves through a special groove to the mouth opening and enters the intestine, where digestion takes place. The eggs are carried and developed in a brood chamber on the back of the female. Juveniles leave her during molting. Basically, cladocerans reproduce parthenogenetically, laying diploid eggs, from which only females hatch. However, under harsh conditions, males hatch from these eggs and fertilize the resulting haploid eggs with haploid sperm, turning them into diploid "resting" ones. Such eggs are laid in pairs in intensely pigmented protective shells that are shed during molting and are able to survive unfavorable periods, and when conditions improve, females are hatched from them, breeding parthenogenetically. Sometimes, under the influence of wind, mass accumulations of such shells are formed along the edge of the coast. Other organisms are also found in zooplankton, such as mysids (Mysis) - small crustaceans that often live in the lower cold oxygen-rich water layers of deep lakes, and a transparent mosquito larva that usually lives at the bottom of lakes. Sometimes there are even freshwater jellyfish with a diameter of up to 38 mm.
CHEMICAL PROCESSES IN LAKES
Although the chemical composition of the lake is important for all organisms, as evidenced, for example, by specialized plant and animal species that live in salt lakes, it is plants that carry out photosynthesis that most strongly affect the chemistry of lake waters. Photosynthesis uses solar energy to convert carbon dioxide and water into hydrocarbons and oxygen. At the same time, in addition to carbon dioxide and water, 18-20 more chemical elements are involved in photosynthesis, and a decrease in the content of any of them below the optimal requirement significantly slows down the process of photosynthesis. This so-called. the hypothesis of the limiting role of nutrients, put forward in the middle of the 19th century. Justus Liebig, is still used in the characterization of aquatic ecosystems. In freshwater bodies, most nutrients are present in quantities in excess of the need for them, but two of them - nitrogen and phosphorus - are relatively rare. It is these elements, individually or together, that limit the process of photosynthesis, or primary production. Moreover, since some blue-green algae are able to bind atmospheric nitrogen, converting it into ammonium and using it in the process of photosynthesis, and phosphorus does not have such a source, the latter becomes the most important limiting element. As a result, many important characteristics of lakes, such as the total increase in primary production or the abundance of algae, are directly dependent on the phosphorus content in lakes. Therefore, lakes are classified according to this indicator. There are oligotrophic lakes (with a low content of nutrients), mesotrophic (with an average content) and eutrophic lakes (with a high content of nutrients). Epilimnion is almost always saturated with dissolved oxygen, which is formed here during photosynthesis, as well as captured from the boundary layer of the atmosphere during the circulation of water. At the same time, all other elements necessary for photosynthesis and growth are extracted from the water by algae, and the chemistry of the waters of the epilimnion undergoes corresponding changes. At the same time, the epilimnion produces a lot of organic detritus, consisting of dead fragments of algae, descending into the hypolimnion. There, dissolved oxygen is used for respiration and decomposition, and many inorganic substances are returned to the water. Thus, in a stratified lake, the initially homogeneous water mass is subdivided into two distinctly different layers: the upper, warmer, with a deficit of available nutrients, and the lower, colder, with a higher concentration of nutrients. In temperate climates, this separation takes place both in winter and summer, although in winter it is less pronounced, since under the ice, due to less access to light, the level of primary water production is significantly reduced. In unstratified lakes, seasonal changes occur throughout the water column. In many lakes rich in nutrients, photosynthesis proceeds so intensively that dissolved oxygen is completely consumed directly at the surface of bottom sediments. In this case, even more significant changes in the chemical composition of water are observed. At the interface between bottom sediments and water, oxygen-containing insoluble iron compounds lose oxygen and become soluble, as a result of which a large amount of iron, manganese, phosphorus and nitrogen enters the water. This process is called internal eutrophication, because in some lakes, as a result of wind mixing or the influence of internal seiches, nutrients released from sediments enter the upper water layer, thus increasing the trophic level of the lake. In temperate regions, during the period of spring and autumn mixing of waters, the surface layer of sediments again absorbs oxygen, all differences in the chemical composition of water in depth disappear, and the water mass again becomes chemically homogeneous.
LAKE DEPOSITS
Lacustrine deposits, which play an important role in the chemistry of lakes, are mostly formed in the lakes themselves. Usually they consist of semi-decomposed remains of algae, zooplankton and larger organisms, and in lakes formed about 10 thousand years ago, they can reach a large thickness (about 20 m). The study of lacustrine sediment cores shows that the concentration of bacteria in them is very high, especially at the contact of bottom sediments and water. The same pattern can be traced in the concentration of various chemicals, such as phosphorus and ammonium. Since lacustrine sediments are usually cold and poor in oxygen, they provide excellent evidence of the state of the lake in the past, which is reflected either in the composition and quantity of specific algae pigments, or in the composition of identifiable remains of the most decay-resistant parts of organisms. Various methods have been developed to determine the age of individual layers of lacustrine sediments. Among them are methods based on the use of natural radioactive isotopes of lead 210Pb and carbon 14C; correlation of marker horizons in sediments, such as ash, with historical data on eruptions of nearby volcanoes. The study of sediments makes it possible to recreate a detailed picture of the changing conditions in a given lake. In addition, since lake sediments accumulate information about the natural conditions of the entire drainage basin, they also capture past climatic changes. For example, studying the composition of plant pollen in a lake sediment column allows us to determine which land plants were common at certain stages of geological history, and taking into account the modern environmental requirements of these plant species determines what temperatures and humidity were at that time.
PROBLEMS OF THE STATE OF LAKES
Lakes are ecosystems in which all components are interconnected. In the absence of external influences, the lakes reach a certain state of equilibrium with the environment, which eventually leads to a more or less stable position, when the organisms living in the lakes adapt to the existing conditions. However, lakes are rarely in equilibrium. On the contrary, they are often used as sources of water for irrigation, drinking water, for agricultural purposes, or for the discharge of such products of modern civilization as industrial wastewater, stormwater and agricultural runoff. Lakes are polluted by increasing levels of pesticides, herbicides and airborne organic compounds such as polychlorinated biphenyls, as well as acid rain from pollutant emissions from car engines and thermal power plants. Plant and animal species alien to them penetrate into them, brought in by fishermen on the bottoms of ships and by other random means. Eutrophication, or excessive enrichment of lakes with nutrients from anthropogenic sources, is on the menacing scale, causing significant environmental damage. In some cases, large lakes of economic importance are even under the threat of complete extinction. For example, the volume of water in the Aral Sea (a large salt lake) has now halved as a result of the analysis of the waters of the Amu Darya and Syr Darya flowing into it for irrigation. As a result, its salinity increased almost three times (from 9.6-10.3‰ to 27-30‰). Exposed areas of the seabed are blown by dust storms, which lead to the removal of salts and pesticides and their deposition within the nearby inhabited areas. Lake pollution is a very serious problem. For example, in order to reduce eutrophication of water bodies, many countries have adopted laws to limit the concentration of phosphorus in water that has passed through treatment plants and may enter lakes. A whole science of lake restoration has emerged, based largely on empirical relationships relating indicators such as algae abundance and water clarity to phosphorus concentrations in lake waters. In some regions, water abstraction from lakes is regulated. The use of pesticides is being carefully studied.
LARGEST LAKES IN THE WORLD
Area, thousand km2
Caspian Sea (Asia - Europe), salty 371.0* Upper (USA - Canada) 82.1 Victoria (Kenya, Tanzania, Uganda) 69.4 Huron (USA - Canada) 59.6 Michigan (USA) 57.8 Aral Sea sea ​​(Kazakhstan - Uzbekistan), salty 36.5* Tanganyika (DRC, Burundi, Tanzania, Zambia) 32.9 Baikal (Russia) 31.5 Big Bear (Canada) 31.3 Nyasa (Malawi, Tanzania, Mozambique) 29, 0 Great Slave (Canada) 28.5 Erie (USA - Canada) 25.6 Winnipeg (Canada) 24.3 Balkhash (Kazakhstan), salty 22.0* Ontario (USA - Canada) 19.7 Ladoga (Russia) 17, 7 Chad (Niger, Chad, Cameroon, Nigeria), brackish 16.3* Maracaibo (Venezuela) 13.5 Onega (Russia) 9.7 Air (Australia), salty 9.3* Volta (Ghana) 8.5 Titicaca ( Peru - Bolivia) 8.3 Nicaragua (Nicaragua) 8.0 Athabasca (Canada) 8.0 Reindeer (Canada) 6.7 Rudolf (Kenya - Ethiopia), salty 6.5 Issyk-Kul (Kyrgyzstan), brackish 6.2 Kokunor (Qinghai) (China) Salted 5.7* Torrens (Australia) Salted 5.7* Venern (Sweden) 5.7 Albert (DRC - Uganda) 5.6 Nettilling (Canada) 5.4 Winn ipegosis (Canada) 5.39 Cariba (Zambia - Zimbabwe) 5.31 Nipigon (Canada) 4.9 Gairdner (Australia), salted 4.77* Urmia (Iran), salted 4.69 Manitoba (Canada) 4.66 Forest (US - Canada) 4.47 * The area is not constant.
LITERATURE
Bogoslovsky B.B. lake science. M., 1960 Muraveisky S.D. Rivers and lakes. M., 1960

Collier Encyclopedia. - Open society. 2000 .

Synonyms:

A lake is a closed land depression that collects and accumulates surface and groundwater. Unlike rivers, these are reservoirs of slow water exchange. The total area of ​​all lakes on Earth is 2.7 million square kilometers. They occupy about 1.8% of the land surface.

Lakes are always and everywhere formed according to one scenario - for various reasons, a depression, a low or a fault is formed on the ground - a hollow. If in the future it will be filled with water, a lake will turn out. Everything else is not essential. The location and origin of the lakes is associated with the climate of the area, which determines their nutrition and evaporation, as well as with factors that contribute to the formation of lake depressions. Where the climate is humid, the lakes are full-flowing, fresh and numerous. For the most part, they are flowing here. In arid areas, the lakes are shallow, often salty and endorheic. Thus, the hydrochemical features of lakes are determined by their geographical location.

Lakes are usually classified according to four criteria: the origin of lake basins; the origin of the water mass; water regime and mineral composition (salinity).

Origin of lake basins

By origin, 5 groups of lake basins are distinguished. Tectonic lake basins - are formed as a result of cracks, faults and lowering of the earth's crust. Such lakes are distinguished by their steep slopes and depth. As an example - Lake Baikal, the Dead Sea, Chad, Titicaca.

Volcanic lake basins - are formed in the craters of volcanoes or in the lowlands of lava fields. As an example, we can mention the Kuril Lake in Kamchatka, the lakes of Java and New Zealand. In the photo - lakes in the craters of the Kelimutu volcano.

Glacial (moraine) lake basins - dug by moving glaciers with subsequent erosion and accumulation of water in front of glacial landforms. When a glacier melts, the material brought by it is deposited in the form of hills, ridges, hills and depressions. Such lakes are usually narrow and long, elongated along the melting line of the glacier - the lakes of Finland, Karelia, the Alps, the Urals, and the Caucasus.

Karst lake basins - they arose as a result of failures, sedimentation of soil and erosion of soft rocks - limestone, gypsum, dolomite. As a result, small but deep lake basins are formed.

Damped (dammed or dammed) lake basins - arise as a result of blocking the riverbed by rockfalls. This is how Lake Sevan, a number of lakes in the Alps, the Himalayas and the Caucasus were formed.

But depressions suitable for filling with water can appear in other ways. It all depends on the location and climate - the proximity of the sea, rivers, strong winds, groundwater, permafrost layers in the soil. The result is the same - the formation of a hollow and filling it with water.

Other types of lakes

Limannye lakes are located along the shores of the seas. They represent coastal areas of the sea, separated from it by coastal spits.

Organogenic lakes eventually appear among swamps and coral reefs. Floodplain lakes are associated with changes in the river channel - lakes of the Kuban floodplains, ilmens of the Volga delta. Such lakes have a characteristic horseshoe shape.

The wind creates eolian lakes, which are formed in the hollows of blowing - Lake Teke, Lake Selecty in Kazakhstan and a number of others arose in this way.

Suffosion lakes appear where groundwater is actively washing away small pieces of rock, causing soil to settle. Such lakes are typical for the south of Western Siberia.

Thermokarst sinkhole lakes (pictured) appear when permafrost areas melt. Dips in the ground are formed, filled with melt water. There are many such lakes in the Kolyma Lowland - the very lake region of Russia.

According to the origin of water masses, lakes are divided into two types - atmospheric and relict. atmospheric lakes have never been part of the oceans. There are many such lakes on Earth. Relic (or residual) lakes appeared on the site of the retreating seas - the Caspian, Aral, Ladoga, Onega, Ilmen and others.

According to the water regime, two types of lakes are distinguished - waste and non-drainage. Waste lakes are lakes in which water is exchanged, rivers flow into them and flow out of them. They are usually fresh. Such lakes are often located in areas of excessive moisture.

mineral lakes

Endorheic lakes have inflowing rivers, but no outflowing ones. Evaporation predominates in the water flow of such lakes, and all mineral substances remain in the reservoir. Most of them are salty. Such lakes are located in areas of insufficient moisture.

According to salinity, four types of lakes are distinguished - fresh, salty, brackish and mineral. Fresh lakes - if the salinity does not exceed 1 ppm. Salt lakes - if the content of soluble substances in them is in the range of 24.7 - 47 ppm. Brackish - salinity up to 24 ppm. Mineral - 47 ppm. It can be soda, sulfate, chloride lakes. In mineral lakes, salts can precipitate, for example, lakes Elton and Baskunchak, which are a source of salt production. Pictured is a salt lake in Kenya.

Lakes play an important role in the planet's ecosystem. They create a special microclimate favorable for different forms of life. Even when salty, they attract many different organisms. And freshwaters form their own balanced and surprisingly rich ecosystems. Geological forces tend to level the surface of the continent through erosion, the accumulation of sediment leads to a decrease in the depth of the lake and its gradual disappearance. Biological and chemical reactions take place in the waters of lakes, as a result of which some elements pass into bottom sediments or, conversely, dissolve in water. Bottom sediments change the relief of the lake bottom and, under certain conditions, can be transformed into rocks of organic origin. Overgrowth of lakes creates new landforms.

Most of the lakes are relatively young formations. One of the most ancient is Baikal. Its age is 25 - 30 million years. The largest of the lakes is the Caspian. Its area is about 368 thousand square kilometers. The deepest - Baikal - 1620 meters. I would like to hope that these amazing natural formations will remain in their original state for a long time to come.

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How many closed depressions are there on land in which water accumulates. When water does not have time to evaporate, it forms lakes. That's what a lake is!

Definition of "lake"

A lake is an accumulation of water in a natural depression on land. It consists of a lake bowl or a bed filled with water to the brim. This body of water is not connected to the sea and ocean. Knowing what a lake is, it is easier to understand its origin. And it differs significantly. There is a lake: tectonic, glacial, river, seaside. There are also failure, mountain, crater and artificial.

Lake features

What is a lake, what are its features? First, unlike rivers, lakes do not have currents and are not part of the oceans. Secondly, lakes have different mineralization of water. the deepest and fresh lake- Baikal. And the largest lake, and, in terms of salt composition, similar to ocean water, is the Caspian. Once it was the sea, as it was connected to the ocean.

There is also a division of lakes according to their position, according to the water balance, according to the chemical composition of the water and according to the nutritional value of the substances contained in the lake.

There are really a lot of features. There are lakes of different shapes, sizes, bottom topography. So, small lakes are called lagoons, and larger ones are called "seas". They receive water not only from rain, but also from underground rivers. Such close "cooperation" allows the rivers not to dry up. Often lakes even give life to new rivers.

There are more than two million freshwater and salt lakes in Russia. The largest lakes in the European part of the country include Ladoga (17.87 thousand km²) and Onega (9.72 thousand km²) in the northwest, Lake Peipsi (3.55 thousand km²) on the Estonian border, as well as the Rybinsk reservoir ( 4.58 thousand km²) on the Volga north of Moscow.

Narrow lakes from 160 to 320 km in length are located behind the dams on the Don, Volga and Kama. In Siberia, similar artificial lakes are located on the upper Yenisei and its tributary, the Angara, where the 570 km long Bratsk reservoir is one of the largest in the world. But they are all insignificant compared to Lake Baikal, the largest reservoir of fresh water on the planet. With a length of 636 km and an average width of 50 km, the surface area of ​​Lake Baikal is 31.72 thousand km², and the maximum depth is 1642 m.

There are countless smaller lakes, located mainly in the poorly drained lowlands of the Russian and West Siberian Plains, especially in the more northern regions. Some of them reach significant sizes, in particular, Lake Beloe (1.29 thousand km²), Topozero (0.98 thousand km²), Vygozero (0.56 thousand km²) and Lake Ilmen (0.98 thousand km²) on the territory of the European north-west of the country, and Lake Chany (1.4-2 thousand km²) in south-west Siberia.

List of the largest lakes in Russia

We present to your attention the 10 largest lakes of the Russian Federation with a description, photo and geographical location on the map of the country.

Caspian Sea

The Caspian Sea is the world's largest inland water body (area: 371 thousand km²). It is called a sea, not a lake, because the ancient Romans who arrived in this region discovered that its water was salty and named it the sea after the tribes of the Caspian who lived near the shores of the lake. The Caspian Sea borders the following five countries: Russia, Kazakhstan, Turkmenistan, Azerbaijan and Iran. The main river feeding the lake is the Volga, which provides about 80% of the inflow of the Caspian Sea, and the remaining 20% ​​falls on other smaller rivers.

The Caspian Sea is rich in oil and natural gas but mining of these are under development. Also, the extraction process is hindered by the problem of dividing the natural resources of the lake between the five countries bordering it. About 160 species and subspecies of fish from 60 genera live in the Caspian Sea and the deltas of the rivers flowing into it. About 62% of the species are endemic.

Baikal

Baikal is the deepest (1642 m), the oldest (25-35 million years) and the most voluminous (23.6 thousand km³) of all lakes in the world, it is a superstar reservoir in the field of hydrology, geology, ecology and history. Today, Lake Baikal contains about 20 percent of the fresh water on the Earth's surface, which is comparable in volume to the entire Amazon River basin. Baikal has 27 islands, including one over 70 km long (Olkhon Island).

More than 1,500 species of animals live off the shores of the lake, 80% of which are found nowhere else on the planet. The most famous representative of the Baikal fauna is the seal, which lives exclusively in fresh water. According to some reports, the population of seals is about 100,000 individuals. Also near the lake there are such large predators as wolves, which occupy the top positions of the Siberian food chain, feeding on deer, birds, rodents and smaller predators.

Ladoga lake

Lake Ladoga is the largest freshwater lake in Europe, located in the north-west of Russia, 40 km east of St. Petersburg. The area of ​​the lake is 17.87 thousand km², the volume is 838 km³, and the maximum depth at a point to the west of Valaam Island it reaches 230 m.

The depression of the lake appeared under the influence of glaciers. The northern shores are mostly high and rocky, and are also separated by deep, ice-covered bays. The southern shores have many sandy or rocky beaches, mostly low, slightly concave, overgrown with willow and alder. In some places there are ancient coastal embankments covered with pine trees. The largest tributaries are the Volkhov, Svir and Vuoksa rivers.

48 different species of fish were found in the lake, of which the most common are roach, carp, bream, pike perch, perch and smelt. Of the 48 species, 25 are of commercial importance and 11 are in the important food fish category.

Lake Ladoga also serves as a key stopping point for migratory birds of the North Atlantic Flyway, which typically mark the arrival of spring.

Lake Onega

Lake Onega is the second largest lake in Europe, located in the northwest of the European part of Russia, between Lake Ladoga and the White Sea. It covers an area of ​​9.72 thousand km², 248 km long and up to 83 km wide. The greatest depth is about 127 m.

The basin of the lake was formed by the movement of the earth's crust and glaciers. The high rocky shores in the north and northwest are composed of layered granite and covered with forest. There are deep bays in Petrozavodsk, Kondopoga and Pevenets. The southern shores are narrow, sandy, often swampy or flooded. Lake Onega has about 1650 islands, covering a total of about 260 km², usually in the northern and northwestern bays.

The lake is home to over 40 species of fish, including vendace (a small member of the salmon family), smelt, burbot bream, pike, perch, roach and salmon. Many types of fish have significant economic value.

Taimyr

Taimyr is the second (after Baikal) largest lake in the Asian part of Russia, located in central regions the Taimyr Peninsula. It is located south of the Byrranga mountains, in the zone.

The lake and tundra zone is popular place for birds such as geese, swans, ducks, buzzards, peregrine falcons and snowy owls. Lake Taimyr is home to a large number of fish, including grayling, muksun, char and whitefish. Although the area is relatively remote, depletion of stocks of certain commercial fish species is still observed.

Taimyr is famous for the largest population of reindeer in Eurasia. Also in this region there are such animals as argali, arctic fox, wolf and lemmings. In 1975, the area was re-introduced.

Since 1983, the lake and its environs have been included in the Taimyr nature reserve. Scientists have discovered plutonium in the sediments of the lake, which allegedly entered Taimyr through wind-blown radioactive particles after nuclear testing held on Novaya Zemlya during the Cold War.

Khanka

Lake Khanka has an area of ​​4 thousand km², of which approximately 97% is located in Russia. The maximum depth of the lake is 10.6 m, and the average volume is 18.3 km². The lake is fed by 23 rivers, 8 of which are in China, and the rest in the territory of the Russian Federation. The only outflow is the Sungacha River, which flows east to the Ussuri River, which forms the international border, and flows north where it joins the Amur River.

Khanka is famous for being home to the highest diversity of birds in the entire temperate zone of Eurasia. At least 327 species of nesting, wintering and migratory birds have been sighted in the lake area.

Chudsko-Pskovskoe Lake

Lake Peipus-Pskovskoye is the largest transboundary and fifth (after Ladoga, Onega, Swedish Venern and Finnish Saim) lake in Europe, located on the border between Estonia and Russia. It occupies 3.6% of the total area of ​​the Baltic Sea basin. A total of 30 islands are located on Lake Peipus, and 40 more in the delta of the Velikaya River. Most of them rise only 1-2 m above the water level, and often suffer from floods.

About 54 species of coastal aquatic plants grow in the basin of Lake Peipus-Pskov, including reed, calamus, reeds and various herbs. 42 species of fish live in the waters of the lake, such as smelt, vendace, bream, perch, pike, roach and whitefish. Wetlands serve as important nesting and feeding grounds for migratory birds such as swans, geese and ducks that migrate from the White Sea to the Baltic Sea. The region is home to one of the largest swallow colonies in Estonia.

Ubsu-Nur

Ubsu-Nur is the largest lake in Mongolia in terms of surface area (3.35 thousand km²), as well as the largest salt lake in the country. The Ubsu-Nur basin is one of the most important biodiversity poles of Eurasia. Although most of the lake is in Mongolia, its northeastern shores are located in the Tyva Republic of the Russian Federation.

The lake is shallow, very salty, and is the remnant of a large sea that existed several thousand years ago. The basin covers an area of ​​about 70 thousand km² and is one of the best preserved natural steppe landscapes on the continent. It is here that the northernmost part of the desert and the most southern part tundra.

Reed and freshwater river deltas serve as resting and nesting sites for numerous migratory birds. Over 220 species of birds can be found around the lake, including the black stork, osprey, white-tailed eagle, whooper, and black-headed gull. About 29 different species of fish live in the waters of the lake, one of which is suitable for human consumption. mountainous area serves as a home for Mongolian gerbils, wild sheep and Siberian ibex.

vats

Although Lake Chany is not well known outside of Siberia, it is one of the largest lakes in the country. Chany is a shallow lake with salty and constantly fluctuating water, the level of which can vary from season to season and from year to year. The lands of the lake basin serve as pastures for cattle.

In terms of area, Beloye is the second (after Onega) natural lake in the Vologda region, and the third (after the Rybinsk reservoir). It is one of the ten largest natural lakes in Europe. The lake has a relatively round shape with a diameter of 46 km. Its area is 1.29 thousand km², and the basin area is about 14 thousand km².

The lake is famous for its fish stocks, the most famous delicacy is the Belozersky smelt. The forage base and high level of oxygen create favorable conditions for the life of many species. The following fish species are common in the waters of the lake: perch, pike, bream, ruff, sabrefish, roach, bleak, burbot, chub, rudd, whitefish, ide, tench, asp, dace and gudgeon).

Table of 10 largest lakes in Russia

lake name	Area, km²	Volume, km³	Dimensions, km	Maximum depth, m	Average depth, m
Caspian Sea	371000	78200	1200 by 435	1025	208
Baikal	31722	23615	636 by 79.5	1642	744,4
Ladoga lake	17870	838	219 by 125	230	46,9
Lake Onega	9720	285	248 by 83	127	30
Taimyr	4560	12,8	-	26	2,8
Khanka	4070	18,3	90 to 45	10,6	4,5
Chudsko-Pskovskoe Lake	3555	25	width 50	15	7,1
Ubsu-Nur	3350	35,7	85 to 80	20	10,1
vats	1400-2000	-	91 to 88	7	2,1
White Lake	1290	5,2	46 to 33	20	4

There are a huge number of lakes on our planet. They can differ strikingly from each other both in size, origin, and in other indicators. Then how are they similar, and what is a lake in general?

It is not easy to give a precise definition of this concept. For example, if you say that this is a reservoir surrounded on all sides by land, then this will not be entirely correct. Since those into which rivers flow (or flow out of them), coastline torn.

If we claim that this is a fresh water body, then what about the Dead Sea and others in which the water is salty? We can say that they have no connection with the oceans. But known to all located in South America, connects to the Caribbean Sea.

So what is a lake? It would be more correct to say that this is a reservoir of natural origin on land. First of all, the lakes differ in size from each other. Sometimes in the mountains you can find small ones, only a few tens of meters long, while the largest lake on Earth - the Caspian Sea - has a length of more than 1000 kilometers.

Rainwater flows into the lakes, rivers and streams flow into them, so they must be located in low points of the terrain. But this is not always observed. South American Lake Titicaca is located at an altitude of 3812 meters above sea level.

How are they formed

To understand what a lake is, you need to find out how they arise. There are glacial reservoirs located in troughs of the earth's surface, formed under the enormous weight of an ancient glacier. These depressions gradually filled with melted glacial waters. Most often they are placed large groups are small and deep. There are many of them in Finland, Canada, Siberia.

They are located in high mountain valleys. Sometimes it happens that such a lake appears right before our eyes - during mountain landslides, the riverbed is blocked and water accumulates near the resulting dam. Usually they are short-lived, and water quickly erodes the barrier, but there are exceptions. An example is the Pamirs.

The lakes formed in elongated, narrow and very deep. There are many of them in Africa: Tanganyika, Nyasa and others. This is the deepest lake in the world, Lake Baikal.

Reservoirs of tectonic origin may also have a shallow depth, for example, the Khmelev lakes, which are located in the eastern part.

Alpine lakes filled with glacial water are only fresh. But the Dead Sea, located in the basin, is so salty that there is no life in it.

In some lakes, due to the presence of a large amount of impurities in its composition, the water is not only salty, but also cloudy, which gives it a different color. But most reservoirs, especially small ones, have fresh and clean water. For example, in Leningrad region Lake Bezymyannoye is located, which is considered one of the cleanest in Russia. The reason for this is the presence of a large number of springs and springs, constantly renewing and refreshing the water.

Some of the lakes regularly change their size, and on the maps their coastline is indicated conditionally. Most often it depends on the seasonal precipitation. So, Lake Chad on the African mainland can change several times during the year.