Glacial lakes of Russia. Tectonic lakes How long do lakes live?

The uniqueness of natural lakes lies in a number of their special characteristics. They are characterized by slow water exchange, free thermal conditions, a unique chemical composition, and differences in water levels.

In addition, they create their own microclimate and cause changes in the surrounding landscape. They accumulate mineral and organic substances, some of which are valuable and useful.

Geographical object "lake" (meaning)

There are about 5,000,000 lakes in our world. Lakes on the globe occupy almost 2% of the surface, which is almost 2.6 million km 3 . Being a component of the hydrosphere, classical natural lakes, are bodies of natural origin, which are lake bowls of water that do not have direct contact (contact) with the sea or ocean. There is a whole science that studies them - limnology. However, there are also anthropogenic lakes that arose as a result of human activity.

If we consider the lake as geographical feature, then its definition becomes more clear: it is a hole on land with closed edges into which flowing water falls and, as a result, accumulates there.

Characteristics of lakes

To give an accurate description of a specific lake, you need to determine its origin, position (above or underground), type of water balance (waste or not), salinity parameters (fresh or not), its chemical composition etc.

In addition, the following parameters need to be accurately determined: the total area of ​​the water surface, the total length of the shoreline, the maximum distance between opposite shores, the average width of the lake (calculated by dividing the area by the previous indicator), the volume of water that fills it, its average and maximum depth .

Types of lakes by origin

The generally accepted classification of lakes by origin factor is as follows:

1. Anthropogenic (artificial) - created by man;
2. Natural - arose naturally (exogenous or endogenous - either from within the Earth, or as a result of processes on its surface), without human intervention.

Natural lakes, in turn, have their own division based on the principle of origin:

• Tectonic - cracks in the earth's crust that have arisen for one reason or another are filled with water. The most famous lake of this type is Baikal.
• Glacial - the glacier melts and the resulting water creates a lake in the basin of the glacier itself or any other. Such lakes, for example, are in Karelia and Finland: lakes appeared along the trajectory of the glacier along tectonic cracks.
• Oxbow lake, lagoon or estuary - a decrease in water level cuts off part of the river or ocean.
• Karst, suffusion, thermokarst, aeolian - leaching, subsidence, thawing, blowing, respectively, create a depression that is filled with water.
• A dammed lake occurs when a landslide or earthquake cuts off part of the water surface from the main body of water by a land bridge.
• Water often also collects in mountain basins and craters of volcanoes or their eruption channels.
• And others.

The importance of lakes in nature and for humans

Lakes are natural reservoirs of water that can regulate river flow: receive excess water and, conversely, release part of it when the water level in the river generally decreases. A large water mass has a large thermal inertia, the effect of which can significantly soften the climate of nearby areas.

Lakes are an important object for fishing, organizing salt production, and laying waterways. Water from lakes is often used for water supply. Reservoirs can be used to organize the energy reservoir of a hydraulic installation. Sapropels are extracted from them. Some lake muds have medicinal properties and are used in medicine. The importance of lakes in the planet’s ecosystem can hardly be overestimated; they are an organic element of the entire natural mechanism.

The largest lakes in the world

Among the lakes there are two main record holders:

The Caspian Sea is the largest in area (376,000 km 2), but relatively not deep (30 m);

(Lake Baikal)

Baikal - depth record (1620 meters!).

The average record holders for largest lakes are tectonic lakes.

Not having a direct connection to the sea. Lakes occupy about 1.8% of the land surface, but are distributed extremely unevenly.

Lakes vary in size by area. Especially the largest of them are even called seas ().

Based on the origin of lake depressions, they are distinguished:

• tectonic. These are usually the deepest lakes formed on site (Baikal - depth 1620 m; - 1470 m). The depth of most lakes of tectonic origin is usually less than 1000 m. The bottoms of the deepest lakes lie below ocean level (the bottom of Lake Baikal is 1165 m below ocean level;
• volcanic. These are lakes formed in craters or calderas, as well as in depressions on the surface of lava flows: lakes, Kronotskoye Lake, lakes and Java;
• glacial. These are lakes that formed in areas subject to continental glaciation. They were created either as a result or as a result of glaciation. The glacial erosion type includes lakes located in, in (), (Russia), in the northeast. The shape of these lakes is long, narrow, and they are elongated in the direction of the glacier movement. Lakes that arose as a result of lacustrine accumulation are confined to areas of hilly-moraine relief (see Glaciation). Some lakes occupy lowlands between hills and usually have a lobed shape and shallow depths (). Others arose among moraine topography. They are wide, oval and small: , White;
• karst. They are located in or in sinkholes and occur in areas composed of soluble rocks. Thermokarst basins are formed in the regions, due to the melting of fossil ice and permafrost, as well as ground subsidence. Many tundra lakes are thermokarst;
• coastal lakes. They were formed as a result of the separation of part of the sea from the rest by sediments of sand or silt. There are many estuaries and lagoons on the coast and;
• dammed lakes occur when a watercourse is dammed by landslides, landslides, lava flows, etc. Thus, in 1911, Lake Sarez was formed with a depth of 505 m. It was dammed by a colossal mountain collapse. Dammed lakes are also common. Many lakes of Sikhote-Alin (Russia), Lake Sevan, Lake Tana () were formed as a result of the damming of the river by lava flows;
• - ponds and;
• oxbow lakes formed during meandering of river beds.

The water mass of lakes is predominantly of origin and enters the lake by condensation on the water surface, when water enters from rivers and streams and due to ground nutrition. The flow of lake water occurs through evaporation and runoff. In some lakes, the modern water mass has replaced the sea mass that occupied the basin in the recent geological past. On the site of modern Ladoga and, as well as in glacial times, there was the Ioldian Sea. After its collapse, lakes formed, first with salty sea water, and then with fresh water. Such lakes are called relict or residual. The animals that live there adapt to the lake's living conditions.

Based on the inflow and outflow of water mass, all lakes are divided into:

• good flow. Rivers flow into and out of them. The water in these lakes is constantly changing. Such lakes are located in zones of excess atmospheric moisture (Baikal, Geneva);
• low-flow. Rivers also flow into them, but much fewer flow out. These lakes are located in an area with insufficient moisture (Balaton, Tanganyika);
• drainless. Formed in zones and. Rivers flow into such lakes, but not a single one flows out (, Dead Sea);
• deaf. They feed on rain or melt water, since rivers do not flow into them or flow out of them. These are small lakes and zones or craters. Karst lakes were excluded from these groups, since they are fed primarily by water.

Lakes can also be divided into:

• fresh(their salinity does not exceed 1%o);
• salty(their salinity ranges from 1 to 47%o);
• (their salinity exceeds 47%o). From them, salts can precipitate (Elton, Baskunchak).

The salinity of Dead Lake is 270%©.

Ozer. In countries with warm climates, it fluctuates slightly throughout the year. In summer, the water temperature decreases with depth. in winter upper layer The water cools below freezing, and the lake becomes covered with ice, and with depth the water temperature rises. The saltier the water, the lower its freezing point. Large, deep lakes take longer to freeze than shallow lakes. Thus, Baikal freezes only at the beginning of January, when all the reservoirs around have long been covered with ice.

According to their biological properties, lakes are divided into:

• to a depth of 1 m there are thickets of sedge, arrowhead, etc.;
• to a depth of 2-3 m - reeds, reeds;
• up to a depth of 4m - submerged plants: pondweed and others.
• lakes poor in nutrients. They are transparent, deep and cold;
• lakes with rich They are usually shallow, well warmed up;
• lakes, poor in life, with brown water that lacks oxygen.

Most lakes are characterized by abundant vegetation, especially in the coastal zone. It is arranged in tiers:
Lakes go through several stages in their development. In more humid climate they overgrow and turn into. In dry climates, lakes dry out; they become salty and have poor vegetation.

The movement of water in lakes, as well as in the seas, manifests itself in the form of currents, but very slow ones, as well as waves that reach large sizes only in large lakes. For example, up to 2-2.5 m are observed in and on. When there are drops in different parts of the lake, standing waves are also observed.

Lakes play a very important role both in nature and in human life. Like the seas, they have a warming effect on the world. Lakes also influence the topography, since they also carry out erosion and accumulative work.

The lake is an element of the hydrosphere. This is a body of water that has arisen naturally or artificially. It is filled within its bed with water and has no direct connection with the sea or ocean. There are about 5 million such reservoirs in the world.

general characteristics

In terms of planetology, a lake is an object that exists stably in space and time, filled with matter in liquid form. In a geographical sense, it is represented as a closed depression of land into which water enters and accumulates. The chemical composition of lakes remains constant for a relatively long time. The substance filling it is renewed, but much less frequently than in the river. At the same time, the currents present in it do not act as the predominant factor determining the regime. Lakes provide regulation. Chemical reactions take place in the waters. During interactions, some elements settle in bottom sediments, others pass into the water. In some bodies of water, which usually do not have a flow, the salt content increases due to evaporation. As a result of this process, a significant change in the salt and mineral composition of the lakes occurs. Due to large thermal inertia, large objects are softened climatic conditions adjacent areas, reducing seasonal and annual meteorological fluctuations.

Bottom sediments

When they accumulate, significant changes occur in the relief and size of lake basins. When reservoirs become overgrown, new forms are formed - flat and convex. Lakes often form barriers to groundwater. This, in turn, causes waterlogging of nearby land areas. There is a continuous accumulation of mineral and organic elements in the lakes. As a result, thick layers of sediment are formed. They change along the way further development bodies of water and turning them into land or swamps. Under certain conditions, bottom sediments are transformed into rock minerals of organic origin.

Features of education

Ponds arise for a variety of reasons. Their natural creators are wind, water, and tectonic forces. On the surface of the earth, depressions can be washed out by water. Due to the action of the wind, a depression is formed. The glacier polishes the depression, and the mountain collapse dams the river valley. This creates a bed for the future reservoir. Once filled with water, a lake appears. In geography, bodies of water are classified depending on the method of formation, the presence of life, and salt concentration. Only the saltiest lakes lack living organisms. Most of reservoirs created due to displacements earth's crust or volcanic eruptions.

Classification

According to their origin, reservoirs are divided into:

Volcanic reservoirs

Such lakes are located in extinct craters and explosion tubes. Such reservoirs are found in Europe. For example, volcanic lakes are present in the Eifel region (in Germany). Near them there is a weak manifestation of volcanic activity in the form of hot springs. The most common type of such lakes is a crater filled with water. Oz. The Mazama volcano crater in Oregon was formed more than 6.5 thousand years ago. Its diameter is 10 km, and its depth is 589 m. Some of the lakes were formed in the process of blocking volcanic valleys with lava flows. Gradually, water accumulates in them and a reservoir is formed. So, for example, a lake appeared. Kivu is a depression of the East African Rift structure, located on the border of Rwanda and Zaire. Flowing once from the lake. Tanganyika r. The Ruzizi flowed along the Kivu Valley north towards the Nile. But from the moment the channel was blocked after the eruption of a nearby volcano, it filled the depression.

Other types

Lakes can form in limestone voids. Water dissolves this rock, forming huge caves. Such lakes can arise in areas of underground salt deposits. Lakes may be artificial. They are usually intended to store water for various purposes. Often, the creation of artificial lakes is associated with various types of excavation work. However, in some cases their appearance is a side effect. For example, artificial reservoirs are formed in mined-out quarries. Among the largest lakes it is worth noting Lake. Nasser, located on the border of Sudan and Egypt. It was formed by damming the river valley. Nile. Another example of a large artificial lake is Lake. Mid. It appeared after the installation of a dam on the river. Colorado. As a rule, such lakes are served by local hydroelectric power stations and provide water to nearby settlements and industrial zones.

Largest glacial-tectonic lakes

One of the main reasons for the formation of reservoirs is due to this displacement in a number of cases, the sliding of glaciers occurs. Ponds are very common on the plains and in the mountains. They can be found both in basins and between hills in depressions. Glacial-tectonic lakes (examples: Ladoga, Onega) are quite common in the Northern Hemisphere. Avalanches left enough deep depressions after myself. Melt water accumulated in them. Sediments (moraine) dammed the depressions. This is how reservoirs in the Lake District were formed. At the foot of the town of Bolshoi Arber there is a lake. Arbersee. This body of water remained after the Ice Age.

Tectonic lakes: examples, characteristics

Such reservoirs are formed in areas of shifts and faults in the crust. Typically, the world's tectonic lakes are deep and narrow. They are distinguished by steep, straight banks. These reservoirs are located mainly in through deep gorges. Tectonic lakes in Russia (examples: Kuril and Dalnee in Kamchatka) are characterized by a low bottom (below the ocean level). Yes, lake. Kurilskoe is located in the southern part of Kamchatka, in a picturesque deep basin. The area is surrounded by mountains. Maximum depth reservoir - 360 m. It has steep banks from which many mountain streams flow. The river flows from the reservoir. Ozernaya. Hot springs come to the surface along the banks. In the center of the lake there is a small hill - an island. It is called the "heart stone". Not far from the lake there are unique deposits of pumice. They are called Kutkhin bats. Today the lake Kurilskoye is a nature reserve and declared a zoological natural monument.

Bottom profile

The glacial-tectonic lakes of the world have a sharply defined relief. It is presented in the form of a broken curve. Glacial deposits and accumulative processes in sediments may not have a significant effect on the clarity of basin lines. However, in some cases the impact can be quite noticeable. Glacial tectonic lakes may have a bottom covered with “scars.” They are quite clearly visible on islands and rocky shores. The latter are composed mainly of hard rocks. They are weakly susceptible to erosion, which, in turn, causes a low rate of sediment accumulation. Such tectonic ones are classified as a=2-4 and a=4-10. The deep-water zone (over 10 m) of the total volume is 60-70%, shallow water (up to 5 m) - 15-20%. Tectonic lakes are characterized by heterogeneity of water in terms of thermal parameters. During the maximum heating of the surface, the temperature of the bottom waters remains low. This is due to stable thermal stratifications. Vegetation is quite rare. It can be found along the shores in closed bays.

Spreading

Where, besides Kamchatka, are tectonic lakes found? The list of the most famous bodies of water in the country includes such formations as:

1. Sandalwood.
2. Sundozero.
3. Palier.
4. Randozero.
5. Salvilambi.

These reservoirs are located in the Suna River basin. Tectonic lakes are also found in the forest-steppe Trans-Urals. Examples of reservoirs:

1. Welgi.
2. Argayash.
3. Shablish.
4. Quiet.
5. Sugoyak.
6. Kaldy.
7. B. Kuyash and others.

The depth of reservoirs on the Trans-Ural Plain does not exceed 8-10 m. Based on their origin, they are classified as lakes of the erosion-tectonic type. Their depressions changed accordingly under the influence of erosion processes. Many reservoirs in the Trans-Urals are confined to ancient river hollows. These are, in particular, tectonic lakes such as Kamyshnoye, Alakul, Peschanoye, Etkul and others.

Unique body of water

In the southern part Eastern Siberia the lake is located Baikal is a tectonic lake. Its length is more than 630 km, and its length coastline- 2100 km. The width of the reservoir varies from 25 to 79 km. total area lakes - 31.5 sq. km. This reservoir is considered the deepest on the planet. It contains the largest volume of fresh water on Earth (23 thousand m3). This is 1/10 of the world supply. Complete renewal of water in the reservoir occurs in 332 years. Its age is about 15-20 million years ago. Baikal is considered one of the oldest lakes.

Terrain

Baikal lies in a deep depression. It is surrounded by mountain ranges covered with taiga. The area around the reservoir has a complex, deeply dissected topography. Not far from the lake itself there is a noticeable expansion of the mountain strip. The ridges run parallel to each other here in the direction from northwest to southeast. They are separated by basin-like depressions. River valleys run along their bottom, and in some places small tectonic lakes are formed. Shifts of the earth's crust take place in this area today. This is indicated by relatively frequent earthquakes near the basin, hot springs coming to the surface, as well as subsidence of large areas of the coast. The water in the lake is blue-green. It is distinguished by exceptional transparency and purity. In some places you can clearly see stones lying at a depth of 10-15 m and thickets of algae. The white disk, lowered into the water, is visible even at a depth of 40 m.

Distinctive features

The shape of the lake is a nascent crescent. The reservoir stretches between 55°47" and 51°28" north. latitude and 103°43" and 109°58" east. longitude The maximum width in the center is 81 km, the minimum (opposite the Selenga River delta) is 27 km. The lake is located above sea level at an altitude of 455 m. 336 rivers and streams flow into the reservoir. Half of the water comes from the river. Selenga. One river flows out of the lake - the Angara. It should, however, be said that in the scientific community there are still discussions about the exact number of streams flowing into the reservoir. Most scientists agree that there are fewer than 336.

Water

The liquid substance filling the lake is considered unique in nature. As mentioned above, the water is surprisingly transparent and clean, rich in oxygen. In the recent past, it was even considered healing. Baikal water was used to treat various diseases. In spring its transparency is higher. In terms of indicators, it is approaching the standard - the Sargasso Sea. Its water transparency is estimated at 65 m. During the period of mass algal blooms, the lake’s indicator decreases. Nevertheless, even at this time, in a lull, the bottom can be seen from the boat at a fairly decent depth. High transparency is caused by the activity of living organisms. Thanks to them, the lake is slightly mineralized. The structure of the water is similar to that of distilled water. The importance of the lake Baikal is difficult to overestimate. In this regard, the state provides special environmental protection to this area.

- a body of water formed on the surface of the land in a natural depression. Since the lake does not have a direct connection with the ocean, it is a body of slow water exchange.

The total area of ​​lakes on the globe is about 2.7 million km 3, which is 1.8% of the land surface.

Main characteristics of the lake:

• lake area - water surface area;
• coastline length - water edge length;
• lake length - the shortest distance between the two most distant points on the coastline, average width - area to length ratio;
• lake volume - volume of the basin filled with water;
• average depth - ratio of water mass volume to area;
• maximum depth - is found by direct measurements.

The largest lake on Earth by water surface area is the Caspian (376 thousand km 2 at a water level of 28 m), and the deepest is Baikal (1620 m).

The characteristics of the largest lakes in the world are given in table. 1.

Each lake has three interconnected components: basin, water mass, vegetation and animal world reservoir

Lakes of the world

By position In the lake basin, lakes are divided into above-ground and underground. The latter are sometimes filled with juvenile water. The subglacial lake in Antarctica can also be classified as an underground lake.

Lake basins could be like endogenous, so exogenous origin, which most significantly affects their size, shape, and water regime.

The largest lake basins. They can be located in tectonic depressions (Ilmen), in foothill and intermountain troughs, in grabens (Baikal, Nyasa, Tanganyika). Most large lake basins have a complex tectonic origin; both fault and fold movements are involved in their formation (Issyk-Kul, Balkhash, Victoria, etc.). All tectonic lakes are large in size, and most have significant depths and steep rocky slopes. The bottoms of many deep lakes lie below the level of the World Ocean, and the surface of the lake lies above the level. Certain patterns are observed in the location of tectonic lakes: they are concentrated along faults in the earth’s crust or in rift zones (Syrian-African, Baikal), or frame shields: along the Canadian shield are located the Great Bear Lake, the Great Slave Lake, the Great North American Lakes, along the Baltic Shield — Onega, Ladoga, etc.

Volcanic lakes occupy craters and calderas extinct volcanoes(Kronopkoye Lake in Kamchatka, lakes in Java, New Zealand).

Along with lake basins created by internal processes of the Earth, there are very numerous lake baths formed due to exogenous processes.

Among them the most common glacial lakes on the plains and in the mountains, located both in basins plowed by glaciers and in depressions between hills with uneven deposition of moraine. The lakes of Karelia and Finland, which are elongated in the direction of glacier movement from northwest to southeast along tectonic cracks, owe their origin to the destructive activity of ancient glaciers. In fact, Ladoga, Onega and other lakes have a mixed glacial-tectonic origin. Glacial basins in the mountains include numerous, but small carts lakes located in bowl-shaped depressions on mountain slopes below the snow line (in the Alps, Caucasus, Altai), and trogous lakes - in trough-shaped glacial valleys in the mountains.

The uneven accumulation of glacial deposits on the plains is associated with lakes among hilly and moraine terrain: in the north-west of the East European Plain, especially in the Valdai Upland, in the Baltic states, Poland, Germany, Canada and the northern USA. These lakes are usually shallow, wide, with lobed shores, with islands (Seliger, Valdai, etc.). In the mountains, such lakes arose on the site of former glacier tongues (Como, Garda, Würm in the Alps). In areas of ancient glaciations, there are numerous lakes in the hollows of the runoff of melted glacial waters; they are elongated, trough-shaped, usually small and shallow (for example, Dolgoe, Krugloe - near Moscow).

Karst lakes are formed in places where rocks are leached by underground and partly surface waters. They are deep, but small, often round in shape (in the Crimea, the Caucasus, in the Dinaric and other mountainous regions).

Suffosion lakes are formed in basins of subsidence origin at the site of intensive removal of fine earth and mineral particles by groundwater (southern Western Siberia).

Thermokarst Lakes appear when permafrost soil melts or ice melts. Thanks to them, the Kolyma Lowland is one of the most lake regions in Russia. Many relict thermokarst lake basins are located in the north-west of the East European Plain in the former periglacial zone.

Aeolian lakes arise in blowing basins (Lake Teke in Kazakhstan).

Zaprudnye lakes are formed in the mountains, often after earthquakes, as a result of landslides and landslides blocking river valleys (Lake Sarez in the Murghab valley in the Pamirs).

In the valleys of lowland rivers, the most numerous are floodplain oxbow lakes of a characteristic horseshoe shape, formed as a result of meandering of rivers and subsequent straightening of channels; when rivers dry up, river lakes are formed in bochagas - reaches; in river deltas there are small ilmen lakes, in place of channels, often overgrown with reeds and reeds (ilmen lakes of the Volga delta, lakes of the Kuban flood plains).

On the low-lying coasts of the seas, coastal lakes are typical in place of estuaries and lagoons, if the latter are separated from the sea by sandy alluvial bridges: spits, bars.

A special type is organogenic lakes among swamps and coral buildings.

These are the main genetic types of lake basins, determined by natural processes. Their location on the continents is presented in Table. 2. But recently, more and more “man-made” lakes created by man have appeared - so-called anthropogenic lakes: lakes - reservoirs on rivers, lakes - ponds in quarries, in salt mines, on the site of peat mining.

By genesis of water masses There are two types of lakes. Some have water of atmospheric origin: precipitation, river and groundwater. Such lakes fresh, although in dry climates they may eventually become salty.

Other lakes were part of the World Ocean - these are relict salty lakes (Caspian, Aral). But even in such lakes, primary sea water can be greatly transformed and even completely displaced and replaced by atmospheric waters (Ladozhskoye, etc.).

Table 2. Distribution of the main genetic groups of lakes by continent and part of the world

Depending from water balance, t.s. According to the conditions of inflow and outflow, lakes are divided into drainage and drainageless. Lakes that discharge part of their waters in the form of river runoff - sewage; a special case of them are flowing lakes. Many rivers can flow into the lake, but only one flows out (the Angara from Lake Baikal, the Neva from Lake Ladoga and etc.). Lakes that do not drain into the World Ocean - drainless(Caspian, Aral, Bolshoye Solenoye). The water level in such lakes is subject to fluctuations of varying duration, which is primarily due to long-term and seasonal climate changes. At the same time, the morphometric characteristics of lakes and the properties of water masses change. This is especially noticeable on lakes in arid regions, which promise long cycles of climate moisture and aridity.

Lake waters, like other natural waters, are characterized by different chemical compositions and varying degrees of mineralization.

Based on the composition of salts in the water, lakes are divided into three types: carbonate, sulfate, and chloride.

By degree of mineralization lakes are divided into fresh(less than 1%o), brackish(1-24.7%c), salty(24.7-47%o) and mineral(more than 47%c). An example of a fresh lake is Baikal, the salinity of which is 0.1%, brackish - Caspian sea water - 12-13%, Bolshoye Solenoye - 137-300%, Dead Sea - 260-270%, in some years - up to 310%c.

In the distribution of lakes with varying degrees of mineralization on earth's surface There is a geographic zonality determined by the moisture coefficient. In addition, those lakes into which rivers flow are characterized by low salinity.

However, the degree of mineralization can vary within the same lake. For example, in the closed lake Balkhash, located in an arid zone, in the western part, where the river flows. Or, the water is fresh, but in the eastern part, which is connected to the western part only by a narrow (4 km) shallow strait, the water is brackish.

When lakes become oversaturated, salts begin to precipitate from the brine and crystallize. Such mineral lakes are called self-planting(for example, Elton, Baskunchak). Mineral lakes in which lamellar fine needles are deposited are known as mud.

Plays an important role in the life of lakes thermal regime.

Freshwater lakes in the hot thermal zone are characterized by the warmest water at the surface, which gradually decreases with depth. This temperature distribution over depth is called direct thermal stratification. Lakes in the cold thermal zone have the coldest (about 0 °C) and lightest water at the top almost all year round; With depth, the water temperature increases (up to 4°C), the water becomes denser and heavier. This temperature distribution over depth is called reverse thermal stratification. Lakes in the temperate thermal zone have variable stratification by season: direct in summer, reverse in winter. In spring and autumn there come moments when the vertical temperature is the same (4 °C) at different depths. The phenomenon of constant temperature over depth is called homothermy(spring and autumn).

The annual thermal cycle in temperate lakes is divided into four periods: spring heating (from 0 to 4 °C) is due to convective mixing; summer heating (from 4 °C to maximum temperature) - by molecular thermal conductivity; autumn cooling (from maximum temperature to 4 °C) - by convective mixing; winter cooling (from 4 to 0 °C) - again by molecular thermal conductivity.

IN winter period Freezing lakes have the same three phases as rivers: freezing, freezing, opening. The process of ice formation and melting is similar to rivers. Lakes tend to be covered with ice for 2-3 weeks longer than rivers in the region. The thermal regime of freezing salt lakes resembles that of seas and oceans.

Dynamic phenomena in lakes include currents, waves and seiches. Katabatic currents occur when a river flows into a lake and water flows out of the lake into the river. In flowing lakes they can be traced throughout the entire water area of ​​the lake, in non-flowing lakes - in areas adjacent to the mouth or source of the river.

The height of the waves on the lake is less, but the steepness is greater compared to the seas and oceans.

The movement of water in lakes, along with dense convection, promotes mixing of water, penetration of oxygen into the lower layers, and uniform distribution of nutrients, which is important for the very diverse inhabitants of lakes.

By nutritional properties of water mass and the conditions for the development of life, lakes are divided into three biological types: oligotrophic, eutrophic, dystrophic.

Oligotrophic- low-nutrient lakes. These are large, deep, transparent lakes with greenish-blue water, rich in oxygen, so organic residues are intensively mineralized. Due to the small amount of nutrients, they are poor in plankton. Life is not rich, but there are fish and crustaceans. These are many mountain lakes, Baikal, Geneva, etc.

Eutrophic the lakes have a high content of nutrients, especially nitrogen and phosphorus compounds, are shallow (up to 1015 m), well heated, with brownish-green water. The oxygen content decreases with depth, which is why fish and other animals die in winter. The bottom is peaty or muddy with an abundance of organic residues. In summer, water blooms occur due to the strong development of phytoplankton. The lakes have a rich flora and fauna. They are most common in forest-steppe and steppe zones.

Dystrophic the lakes are poor in nutrients and oxygen and are shallow. The water in them is acidic, slightly transparent, and brown due to the abundance of humic acids. The bottom is peaty, there is little phytoplankton and higher aquatic vegetation, as well as animals. These lakes are common in heavily swampy areas.

In the last decade, due to the increased supply of phosphorus and nitrogen compounds from fields, as well as the discharge of wastewater from some industrial enterprises, eutrophication of lakes has been observed. The first sign of this unfavorable phenomenon is a strong bloom of blue-green algae, then the amount of oxygen in the reservoir decreases, silt forms, and hydrogen sulfide appears. All this will create unfavorable living conditions for fish, waterfowl, etc.

Evolution of lakes occurs in different ways in humid and dry climates: in the first case they gradually turn into swamps, in the second - into salt marshes.

In a humid (humid) climate, the leading role in filling the lake and turning it into a swamp belongs to vegetation, partly to the remains of the animal population, which together form organic remains. Temporary streams and rivers bring mineral deposits. Small lakes with gentle shores are overgrown by pushing vegetation ecological zones from the periphery to the center. Eventually the lake becomes a grassy, ​​low-lying marsh.

Deep lakes with steep banks overgrow differently: by growing from above alloys(swell) - a layer of living and dead plants. It is based on plants with long rhizomes (cinquefoil, cinquefoil, whitewing), and other herbaceous plants and even shrubs (alder, willow) settle on the network of rhizomes. The float first appears on the shores, protected from the wind, where there is no waves, and gradually advances onto the lake, increasing in power. Some plants die and fall to the bottom, forming peat. Gradually, only “windows” of water remain in the ravine, and then they disappear, although the basin is not yet filled with sediments, and only over time the raft closes with the peat layer.

In dry climates, lakes eventually become salt marshes. This is facilitated by an insignificant amount of precipitation, intense evaporation, a decrease in the influx of river water, and the deposition of solid sediments brought by rivers and dust storms. As a result, the water mass of the lake decreases, the level decreases, the area decreases, the salt concentration increases, and even fresh lake may first turn into a salt lake (Big Salt Lake V North America), and then into the salt marsh.

Lakes, especially large ones, have a softening effect on the climate of the surrounding areas: they are warmer in winter and cooler in summer. Thus, at coastal weather stations near Lake Baikal the temperature in winter is 8-10 °C higher, and in summer by 6-8 °C lower than at stations outside the influence of the lake. Air humidity near the lake is higher due to increased evaporation.