How to determine the origin of a lake. List, names, descriptions, maps and photos of the largest lakes in Russia. By type of mineralization

A lake is a body of water that does not have a direct connection with the World Ocean. Lakes, like any geographical feature , should be classified according to various aspects: historical, geographical, political, economic, geological, legal and others. IN geographically lakes should be divided into the following types: 1. In relation to the mainland: 1.1. Lakes located in Africa. 1.2. Lakes located in Eurasia. 1.3. Lakes located in Australia. 1.4. Lakes located in North America . 1.5. Lakes located in South America. 1.6. Lakes located in Antarctica. 1.7. Lakes located on islands. 2. In relation to a part of the world: 2.1. Lakes related to Africa. 2.2. Lakes related to Antarctica. 2.3. Lakes related to Asia. 2.4. Lakes belonging to Europe. 2.5. Lakes washing two parts of the world. 2.6. Lakes belonging to Australia and Oceania. 2.7. Lakes related to America. 3. On water balance: 3.1. Endorheic lakes. 3.2. Sewage lakes. 4. According to water salinity: 4.1. Fresh lakes. 4.2. Salt lakes. 4.3. Fresh-salt lakes. 5. Depth: 5.1. Deep-water lakes. 5.2. Lakes of medium depth. 5.3. Shallow lakes. 6. By area: 6.1. Large lakes. 6.2. The lakes are medium in size. 6.3. Small lakes. 6.4. Micro lakes. 7. In relation to the World Ocean basin: 7.1. Lakes belonging to the basin Pacific Ocean . 7.2. Lakes belonging to the Arctic Ocean basin. 7.3. Lakes belonging to the Indian Ocean basin. 7.4. Lakes belonging to the basin. 7.5. Lakes belonging to the endorheic basin. 8. In relation to the islands: 8.1. Lakes with islands inside. 8.2. Lakes with archipelagos inside them. 8.3. Lakes with no islands or archipelagos inside. 9. In relation to rivers flowing into the lake: 9.1. Lakes into which only one river flows. 9.2. Lakes into which two rivers flow. 9.3. Lakes into which three or more rivers flow. 9.4. Lakes into which rivers do not flow. 10. In relation to rivers flowing from the lake: 10.1. Lakes from which a river flows. 10.2. Lakes from which the river does not flow. 11. By status: 11.1. Lakes of the first order. 11.2. Lakes of the second order. 12. In relation to the equator: 12.1. Lakes located in the Northern Hemisphere. 12.2. Lakes located in the Southern Hemisphere. 12.3. Lakes located in the Northern and Southern Hemispheres. 13. In relation to the Greenwich meridian: 13.1. Lakes located in the Western Hemisphere. 13.2. Lakes located in the Eastern Hemisphere. 13.3. Lakes located in the Western and Eastern Hemispheres. 14. In relation to reservoirs: 14.1. Lakes that are part of a reservoir. 14.2. Lakes that are not part of a reservoir. All lakes existing in the world should be divided into lakes of the first order and lakes of the second order. Most lakes on Earth are classified as first-order lakes. Second-order lakes include lakes that are integral part any lake of the first order. For example, Lake Peipus consists of three lakes of the second order: Lake Pskov, Lake Teploye and Lake Peipus. Lakes are found on all continents. The following lakes are located in Europe: 1. Lake Constance. Located on the border of Switzerland, Germany and Austria. Refers to the Atlantic Ocean basin. 2. Lake Geneva . Territory of Russia. 5. Lake Neuchâtel. Refers to the Atlantic Ocean basin. Territory of Switzerland. 6. Lake Balaton. Shallow lake. Located in Hungary. Refers to the Atlantic Ocean basin. 7. Lake Baskunchak. Shallow, salty lake. Located in Russia. 8. Lake Vänern. Territory of Sweden. Refers to the Atlantic Ocean basin. 9. Lake Vättern. Located on the Scandinavian Peninsula. Refers to the Atlantic Ocean basin. 10. Lake Vozhe. This shallow lake is located in Russia. Belongs to the Arctic Ocean basin. 11. Lake Vygozero. It is a shallow lake. Belongs to the Arctic Ocean basin. 12. Lake Garda. Refers to the Atlantic Ocean basin. 13. Lake Ilmen. Shallow lake. Territory of Russia. Refers to the Atlantic Ocean basin. 14. Lake Imandra. Territory of Russia. 15. Lake Inarijärvi. Located in Finland. 16. Lake Como. Refers to the Atlantic Ocean basin. 17. Lake Lago Maggiore. Located on the border of Italy and Switzerland. 18. Lake Lacha. Belongs to the Arctic Ocean basin. Territory of Russia. It is a shallow lake. 19. Lake Lezina. Refers to the Atlantic Ocean basin. This is a shallow lake. 20. Lake Mälaren. Part of Sweden. Refers to the Atlantic Ocean basin. 21. Lake Prespa. Located on the border of Greece, Albania and Macedonia. Refers to the Atlantic Ocean basin. 22. Lake Päijänne. Refers to the Atlantic Ocean basin. 23. Lake Saimaa. Refers to the Atlantic Ocean basin. 24. Lake Segozero. Belongs to the Arctic Ocean basin. 25. Lake Seliger. Shallow lake. Territory of Russia. 26. Lake Topozero. Belongs to the Arctic Ocean basin. 27. Lake Shkoder. Located on the Montenegrin-Albanian border. 28. Lake Elton. Shallow, salty lake. Refers to a closed basin. 29. Lake Onega. Located in Russia. 30. Lake Ohrid. Located on the Macedonian-Albanian border. 31. Lake Trasimes. The lake is shallow. 32. Lake Zurich. Refers to the Atlantic Ocean basin. 33. Lake Peipus-Pskov. The lake is shallow. Refers to the Atlantic Ocean basin. This is a salt lake. 4. Lake Alakol. This is a salt lake. 5. Lake Baikal. This is a deep-sea lake. Is in . Located on the French-Swiss border. Refers to the Atlantic Ocean basin. 3. Lake Kubenskoye. This shallow lake is located in Russia. Belongs to the Arctic Ocean basin. 4. . Belongs to the Arctic Ocean basin. 6. Lake Balkhash. This is a shallow lake. Refers to a closed basin. Territory of Kazakhstan. Lake Balkhash should be classified as a fresh-salt lake, since in the western part of the lake the water is fresh, and in the eastern part of the lake the water is salty. 7. Lake Van. This is a salt lake. Located in Turkey. 8. Lake Dongting. Belongs to the Pacific Ocean basin. 9. Lake Essei. Territory of Russia. Belongs to the Arctic Ocean basin. 10. Lake Zaisan. This is a shallow lake. 11. Lake Issyk-Kul. This is a deep-sea lake. Territory of Kyrgyzstan. Refers to a closed basin. 12. Lake Kukunor. The lake is shallow and salty. Territory of China. 13. Lake Lop Nor. This is a salty, drying lake. Territory of China. 14. Lake Nam-Tso. Salt Lake. 15. Poyang Lake. Belongs to the Pacific Ocean basin. Shallow lake. 16. Lake Ritsa. Refers to the Atlantic Ocean basin. 17. Lake Sevan. Located in Armenia. 18. Lake Taimyr. It is a shallow lake. Territory of Russia. Belongs to the Arctic Ocean basin. 19. Lake Tengiz. This is a shallow, salty lake. Territory of Kazakhstan. 20. Tonle Sap Lake. Cambodia territory. Belongs to the Pacific Ocean basin. Shallow lake. 21. Lake Tuz. This is a shallow, salty lake located in Turkey. 22. Lake Uvsu-Nur. Located on the Russian-Mongolian border. Refers to a closed basin. Shallow lake. 23. Lake Urmia. This is a shallow, salty lake. Located in Iran. 24. Lake Khanka. Located on the Russian-Chinese border. Belongs to the Pacific Ocean basin. Shallow lake. 25. Lake Khubsugul. Belongs to the Arctic Ocean basin. 26. Lake El-Milkh. The lake is salty. 27. Lake Teletskoye. Belongs to the Arctic Ocean basin. Territory of Russia. 28. Lake Tiberias. Shallow lake. Lake Tanganyika. This is a deep-sea lake. 9. Lake Chad. This is a shallow lake. Refers to a closed basin. 10. Lake Edward. Located on the Congolese-Ugandan border. Ladoga lake. The lake is deep. 5. Lake Athabasca. Located in Canada. 6. Lake Winnipeg. Shallow lake. Located in Canada. 7. Lake Huron. Located on the US-Canadian border. 8. Lake Managua. Shallow lake. Located in Nicaragua. 9. Lake Michigan. Refers to the Atlantic Ocean basin. 10. Lake Nicaragua. Territory of Nicaragua. Refers to the Atlantic Ocean basin. 11. Lake Ontario. Located on the US-Canadian border. Refers to the Atlantic Ocean basin. 12. Lake Erie. Located on the US-Canadian border. Refers to the Atlantic Ocean basin. 13. Deer Lake. Territory of Canada. Belongs to the Arctic Ocean basin. And on the territory South America The following lakes are located: 1. Lake Argentino. Refers to the Atlantic Ocean basin. 2. Lake Buenos Aires. Located on the border of Chile and Argentina. This is a deep-sea lake. 3. Lake Lagoa-Mirin. Located on the Uruguayan-Brazilian border. Shallow lake. 4. Lake Poopo. Refers to a closed basin. Shallow lake. 5. Lake Titicaca. Located on the Bolivian-Peruvian border. we can, for example, include Lake Karakul, Lake Kukunor, Lake Nam-Tso, Lake Ritsa and Lake Titicaca. Lakes of tectonic origin include lakes such as Baikal, Balaton, Lago Maggiore, Managua, Nicaragua, Prespa, Saimaa, Sasykkol, Tengiz and others. UNESCO, and lakes that are not a UNESCO World Heritage Site. For example, lakes such as Kronotskoye Lake, Kuril Lake, Lake Baikal and Lake Ohrid are UNESCO World Heritage Sites. Regarding lake names, it should be noted that most lakes have the same name. But there are lakes in the world that have two or more names. For example, lakes with two names include lakes such as Lake Murten (the second name is Mora), Lake Albert (the second name is Nyanza), Lake Lagoa-Mirin (the second name is Laguna Merin), Lake Nam-Tso (the second name is name - Tengri-Nur), lake Uvs-Nur (second name - Uvs-Nuur)., and lakes that are not located in the disputed territory. In legal terms, lakes can be classified in relation to states, subjects of states and municipalities on whose territory a particular lake is located. There are lakes in the world that are located on the territory of one state, one subject of a state or one municipality. It must be said that these lakes are the majority. For example, Lake Van is located in Turkey.

Lakes located on the territory of one state should be called intrastate, since they are located within a country. Lakes located on the border of two or more states should be called international. There are enough lakes in the world that are located on the border of two states. For example, Lake Peipus-Pskov is located on the Russian-Estonian border. To the lakes located on

4. Karst lakes, the basins of which arose as a result of failures, soil subsidence and erosion (limestones, gypsum, dolomites). The dissolution of these rocks by water leads to the formation of deep but small lake basins.

5. Dammed (dammed, or dam) lakes arise as a result of blocking the river bed (valley) with blocks of rock during landslides in the mountains (Sevan, Tana, many lakes of the Alps, and other mountain lakes). From a large mountain collapse in 1911, Lake Sarez with a depth of 505 m was formed.

A number of lakes are formed for other reasons:

estuary lakes are common on the shores of the seas - these are coastal areas of the sea, separated from it by means of coastal spits;
oxbow lakes are lakes that arose in old river beds.

Based on the origin of the water mass, lakes are of two types.

1. Fresh lakes— the salinity of which does not exceed 1‰ (one ppm).

2. Brackish - the salinity of such lakes is up to 24‰.

3. Salty - with a content of dissolved substances in the range of 24.7-47‰.

4. Mineral (47‰). These lakes are soda, sulfate, and chloride. In mineral lakes, salts can precipitate. For example, self-settling lakes Elton and Baskunchak, where salt is mined.

Usually wastewater lakes are fresh, since the water in them is constantly renewed. Endorheic lakes are often salty because their water flow is dominated by evaporation, and all minerals remain in the reservoir.

Lakes, like rivers, are the most important Natural resources; used by humans for navigation, water supply, fishing, obtaining mineral salts and chemical elements. In some places small lakes often artificially created by man. Then they are also called .

This list of 50 stunningly beautiful lakes will undoubtedly add to your knowledge and broaden your horizons! This is a list of the world's most famous lakes, but some may be unfamiliar to you.

Lake Victoria
69,485 km2 (26,828 sq mi). The largest lake in Africa. It is a border lake, and.

Lake Tanganyika
32,893 km2 (12,700 sq mi). The lake is not only the 6th largest lake in the world, but it is also the second deepest lake in the world at 1,470 m (4,820 ft) and the longest lake in the world at 676 km (420 mi). Lake Tanganyika is divided between four countries - Tanzania, Democratic Republic Congo, Burundi, Zambia.

Moraine Lake, Canada - Moraine Lake

Lake Pinatubo, Philippines - Lake Pinatubo
Formed only recently (in 1991) after the monsoon, this crater lake is located on the top of Mount Pinatubo, active volcano in the Philippines.

Lake Annette, Canada - Lake Annette

Laguna Colorada, Bolivia - Laguna Colorada, Bolivia
Situated 4,200 meters above sea level in southwestern Bolivia, Laguna Colorada gets its bright red color from pigment deposits and algae beneath its surface. This is an extremely shallow lake with an average depth of 50 cm.

Plitvice Lakes, Croatia /
Located in Croatia, the Plitvice Lakes are actually 16 separate bodies of water, divided into upper and lower basins by natural dams made of moss and algae.

Spotted Lake or Kliluk (Spotted Lake), Canada
In Osoyoos, British Columbia, a 38-acre natural lake that has one of the highest concentrations of minerals in the world.

Dead Sea, Jordan /
The name can be deceiving - in fact, it is the world's deepest hypermineralized lake. It has a salt concentration 8 times greater than the ocean, making it extremely difficult to drown in.

Sheosar Lake, Pakistan
Lake of the Deosai National Park, in the alpine steppe of the Tibetan Plateau.

Riffelsee, Switzerland
Riffelsee is an incredible sight of mirror surface with the Matterhorn mountain in the background.

Peyto Lake, Canada
Peyto Lake is a glacial lake in Banff National Park, Canada. Rocky Mountains. Billa Peyto belongs to the category of colored lakes. The lake has a bright turquoise color, due to a large amount of icy mountain flour creeping into the lake.

Lake Solbjornvannet, Norway

Mirror Lake, California - Mirror Lake - a small, seasonal lake near Tenaya Creek Canyon in the US National Park, Yosemite.

New Zealand also has Mirror Lake, which has amazing reflection properties, like a mirror. It is one of the great lakes of Asia: Issyk-Kul (Kyrgyzstan), Wuhua Hai (China), Inle (Myanmar), Biwa (Japan), Tonle Sap (Cambodia) and Lake Toba in Sumatra (Indonesia).

Horseshoe Lake, Canada - Horseshoe Lake

Emerald Lake, Canada - Emerald Lake

Lake Plastiras, Greece - Lake Plastiras - Lake Plastiras, Greece
The artificial lake in Greece holds up to 400 million cubic liters of fresh water and is one of the highest in Europe.

Mystic Lake, Montana - Mystic Lake
The largest lake in the Beartooth Mountains of Montana offers several world famous hiking trails and incredible views.

Yamdrok Tso lake, Tibet - Yamdrok Tso Lake
This lake in Tibet has over 72 km of peaks and is surrounded by snow-capped mountains.

Lake Malawi, Tanzania - Lake Malawi / Malawi and Mozambique 30,044 km2 (11,600 sq mi). The lake is divided between Tanzania, Mozambique and Malawi. Africa's second deepest lake, this tropical reservoir has more fish species than any other lake on Earth.

Lake Louise, Canada - Lake Louise, Canada

Lake Isabella, Colorado - Lake Isabelle, Colorado
Popular tourist destination, Lake Isabelle has incredible views of the Navajo and Apache peaks.

Crater Lake, Oregon - Crater Lake, Oregon

Barclay Lake, Washington State - Barclay Lake, Washington

Mono Lake, California - Mono Lake
This shallow lake in the Mono County California desert was formed over 760,000 years ago, and has a very similar ecosystem to the Colorada Lagoon.

Ancient underground lake Reed flute, China - Reed Flute Cave. This is a limestone cave in Guangxi, China. More than 180 million years old. Since the 1940s, it has become famous throughout the world due to the colorful caves around the lake.

Lough Ree(Loch RI or Loch Ríbh) is the geographical center of Ireland, the midlands. Lough Ree is the second largest lake on the River Shannon after Lough Derg. The other two large lakes are Lough Allen to the north, and Lough Derg to the south. Province of Leinster in County Roscommon the lake is popular for Irish legends about the monster.

Loch Ness(Loch Ness, Scotland) Scotland. Loch Ness (Gaelic: Loch Niche) is the second largest Scottish lake by surface area after Loch Lomond, but due to its great depth, it is Scotland's largest lake by volume of water. Deep, freshwater lake Lough in Scotland is located approximately 23 miles (37 km) southwest of Inverness. The lake is famous for its Loch Ness monster. Also of interest to tourists is Urquhart Castle east of Drumnadrochit, the lighthouses at Lochend (Bona Lighthouse) and Fort Augusta.

Okanagan Lake- big, deep lake in the Okanagan Valley in British Columbia, Canada. The lake is 135 km long and 4 - 5 km wide. His interesting feature the legend of the Demon of Lake Ogopogo or Naitaka, and the famous terraces that were formed by the periodic lowering of its predecessor, glacial Lake Penticton. The maximum depth of the lake is 232 m in the area of Grant Island (called "Whiskey Island" or "Seagull Island" by locals)

Lake Labynkyr(Labynkyr Lake), Yakutia
This mystical lake is located near the Pole of Cold in the territory of Oymyakon uluss. Legends say that a monster lives deep in the water. It attacks dogs, deer and even people. History tells how one day a monster destroyed an Even caravan.

Kanas Lake(pinyin: Kanasi Hu) is a crescent-shaped lake in Altai Prefecture, Xinjiang Province, China. The lake is located in a valley in the Altai Mountains, on the border with Mongolia and. The lake was formed 200,000 years ago, during the Quaternary period, as a result of glacier movement. The Kanas River, flowing from the lake, merges with the Hemu River, forming the Burkin River, which itself is a tributary of the Irtysh River. Ethnic Tuvans and Kazakhs live in the Kanas Valley.

Lake Kok-Kol(Kok-Kol lake) Mysterious lake in Zhambyl region, Kazakhstan. From time to time, the mysterious lake makes some strange sounds, and sometimes you can see signs of ripples, as if a huge creature is drifting inside the lake. Locals They believe that the lake is bottomless. Indeed, when hydrographers measured its depth, they could not find the bottom. But, they found many channels. This explains the constant water level, despite the fact that nothing flows from or flows into the lake.

Aral Sea(Kazakh: Aral Tenizi; Mongolian: Aral tengis; Tajik: Bakhri Aral; Persian: دریای خوارزم Daryâ- you Khârazm) was a closed lake between Kazakhstan in the north and Uzbekistan in the south. The name roughly translates to “sea of islands” (more than 1,100 islands were scattered across its waters). The catchment covers parts of Tajikistan, Turkmenistan, Kyrgyzstan and Kazakhstan.
Formerly one of the four largest lakes in the world, with an area of 68,000 km 2 (26,300 sq mi), the Aral Sea has been steadily shrinking since 1960 after the rivers that fed the lake were redirected through Soviet irrigation projects. Drying Aral Sea called "one of the worst environmental disasters planets"

Lake Storshen(Swedish pronunciation: Storsjön, lit. "Great Lake") is the fifth largest lake in Sweden, located in the province of Jämtland (Jämtland). The Indalsälven river flows from Storsjön and the lake contains main island Frosson. The city of Östersund is on its east coast, opposite Frösön. Storsjön is considered the birthplace of sea creatures Storsjöodjuret.

Lake Champlain— Lake Champlain lies directly on Burlington, the border between the United States and Canada. At the northern tip is the historically interesting Fort Ticonderoga. Lake Champlain offers cruises and ferries to Vermont and New York.

Lake Natron is saline and soda lake in the Arusha region of northern Tanzania. The lake is located near the Kenyan border in the Eastern Rift Branch of the East African Wetland of International Importance. Lake Natron is a basin of the Ramsar Valley, fed mainly by central Kenya's rivers and hot springs. The unusual color of the water is created by cyanobacteria. Due to high evaporation, salt-loving microorganisms begin to flourish.

Lake Tahoe, North America's largest alpine lake known for its cobalt blue waters and surrounding snow-capped peaks. Lake Tahoe is the state border between the states of California and Nevada, and popular resort Sierra Nevada.

Lake Lucerne— among the most beautiful lakes in Switzerland, it stands out for its amazing panorama of the snow-capped peaks of the Alps, such as the Eiger and Jungfrau. The lake is lined with vintage steamboats that have been sailing here since the 1800s. In spring, the Lake Lucerne basin is fed by Mineralbad streams from the top of Mount Rigi.

Pigeon Lake(Dove Lake) in Tasmania, Australia. Serene Dove Lake - Landmark national park near Cradle Mountain. This lake is the home of the legendary Tasmanian Devil.

Lake Como, Italy - just 45 minutes from vibrant Milan. Lake Como is one of the favorite vacation spots of the rich and famous.

Lake Bled- one of the most charming attractions of the Old Continent. Lake Bled of the Julian Alps (Slovenian: Bled, German: Veldes) is located in Slovenia, near the borders with Italy and Austria.

Lake Synevyr- the largest and most famous lake in the Ukrainian Carpathians. The lake is located in the Gorgany mountain range, in the upper reaches of the Terebly River. The lake has its own beautiful legend about lovers.

The list of the most famous lakes in the world can rightfully include the unnamed:

Lake Ohrid of the Balkan Mountains (located between the Republic of Macedonia and Albania)
Lake Saimaa (Finland)
Ladoga/Onega/Chudskoye (Russia)
Balaton (Hungary)
Annecy (France)
Garda / Iseo (Italy)
Wastwater (England)
Sogne (Norway)
Killarney (Ireland)
Hallstattersee (Austria)
Königsee / Obersi (Germany)
Jökulsádlón (Iceland)
Laguna Verde (Bolivia)
Lençóis Maranhenses (Brazil)
Nakuru (Kenya)
Tekapo (New Zealand)
Lagunas Altiplánicas (Chile)
Laguna Bacalar (Mexico) and many others.

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 Globe occupy almost 2% of the surface, which is almost 2.6 million km 3. As a component of the hydrosphere, classic 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 a lake as a geographical object, then its definition becomes clearer: 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 particular lake, you need to determine its origin, position (above or underground), type of water balance (wastewater or not), mineralization parameters (fresh or not), its chemical composition, etc.

In addition, you need to accurately determine the following parameters: total area water mirror, 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:

Anthropogenic (artificial) - created by man;
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 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 important object for fishing, organizing salt production, 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.

LAKE
a body of water surrounded by land. Lakes range in size from very large ones, such as the Caspian Sea and the Great Lakes of North America, to tiny bodies of water measuring a few hundred square meters or even smaller. The water in them can be fresh, like in a lake. Upper, or salty, as in the Dead Sea. Lakes are found at any altitude, from the lowest absolute elevation on Earth on the land surface -408 m (Dead Sea) to almost the highest (in the Himalayas). Some lakes do not freeze all year round, while others, such as Lake. Vanda in Antarctica are frozen in ice for most of the year. Many lakes exist constantly, while others (for example, Lake Eyre in Australia) are only occasionally filled with water. Despite their diversity, lakes of all types have 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). Perhaps 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 observed 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 climate 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 lakes are probably younger than 12 thousand years, and man-made lakes - artificial reservoirs - are only a few decades old.

EASTERN COAST OF LAKE. TANGANYIKA, confined to the East African Rift Zone.

ORIGIN OF LAKE BATTLES
The lakes fill basins that have different genesis. Because the formation processes of these basins are often dependent on local conditions, lakes are concentrated in certain areas, such as the Lake District in north-west England, the Lake District in Austria and the vast belt of lakes covering 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, aeolian processes, coastal processes, accumulation of organogenic sediments, damming of watercourses by humans or beavers, and meteorite falls. The oldest and deepest existing lakes arose under the influence of tectonic activity, but most lakes were formed due to glacial processes. Nevertheless, the role of the other listed factors is also important.
Tectonic activity. Tectonic basins arise as a result of movements of the earth's crust, and many lake basins of tectonic origin cover a large area and are of ancient age. As a rule, they are very deep. Tectonic processes manifest themselves in different ways. For example, the Caspian Sea is confined to a trough at the bottom of the ancient Tethys Sea. In the Neogene, an uplift occurred, as a result of which the Caspian depression became isolated. Its waters gradually desalinated under the influence of precipitation and river runoff. Lake basin Victoria in East Africa formed as a result of the arched uplift of the surrounding land. The Great Salt Lake in Utah also arose due to tectonic uplift of the area through which the lake previously drained. Tectonic activity often results in the formation of faults (cracks in the Earth's crust), which can become lake basins if the area then undergoes a reverse fault or if a block enclosed between the faults subsides. In the latter case, they say that the lake basin is confined to a graben. Several lakes within the East African Rift System have this origin. Among them is the lake. Tanganyika, formed ca. 17 million years old and characterized by a very large depth (1470 m). Continuing this system to the north are the Dead Sea and Lake Tiberias. Both of them are very ancient. The maximum depth of Lake Tiberias is currently only 46 m. Lakes Tahoe on the border of California and Nevada in the USA, Biwa (a source of freshwater pearls) in Japan and Lake Baikal, which contains the world's largest mass of fresh water (23 thousand km3), are also confined to grabens. ), in Siberia.

Volcanic activity leads to the formation of a variety of lake basins - from small round craters with low sides (maars) to large deep calderas that are 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 clear example of a caldera lake is Lake. Crater in Oregon, formed by the eruption of Mount Mazama ca. 6000 years ago. This picturesque almost round lake has a depth of 608 m (the seventh deepest in the world). In the middle of the lake is Wizard Island, which was created 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 beneath a cooler surface lava horizon, causing the latter to subsidence (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, cinch water flows, contribute to the formation of lakes. However, if the dam collapses or the water overflows, these lakes soon disappear. For example, in 1841, the Indus River in the territory of modern Pakistan was dammed by a landslide caused by an earthquake, and six months later the “dam” collapsed, and a lake 64 km long and 300 m deep was drained in 24 hours. This type of lake 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 (tenth deepest among the world’s lakes). Glacial activity is the most effective factor in creating lake basins. Glaciers several kilometers thick, which in geologically recent times covered most of North America and a significant part of Northern Europe, formed lake basins in a variety of ways, and most lakes in these areas are of glacial origin. For example, many lakes are confined to gouge basins, which were formed by the movement of glaciers over a heterogeneous surface. At the same time, glaciers carried away loose sediments. Thousands of lakes that filled such basins are found in northern Canada, Norway and Finland, where they occupy significant areas.

Tarn lakes are located on the mountain slopes in the upper reaches of troughs. They are characterized by basins shaped like amphitheaters. 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 cross-section. 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 was formed, radiating out from one center in the Lake District in north-west England. They have a similar origin large lakes northern Canada - Athabasca, Great Bear and Great Slave. The depth of the latter reaches 640 m. Even the basins of the Great Lakes, which have a complex genesis, were influenced by glaciers. In addition, lakes are formed when river valleys are dammed by moraines. Finally, during the retreat of glaciers, under the thickness of sediments carried by melted glacial waters outside the glacier, they found themselves buried huge boulders 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 form when soluble minerals and rocks such as limestone, gypsum and rock salt are carried away by water, either forming basins on the surface or forming underground voids whose roofs then collapse. These lakes are not necessarily small: for example, lake. Girot in the 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 produced in rocky soil by flowing water under the influence of the process of evorsion (when holes are drilled due to the friction of stones and other abrasive material against the bottom in whirlpools); river beds are blocked during the removal of river sediments by other rivers and their accumulation. For example, the Mississippi River formed the lake. St. Croix near St. Paul (Minnesota), dammed the St. Croix River, but was then itself dammed downstream by sediment from the Chippewa River, resulting in the formation of Lake. Pippin. Finally, in valleys with well-developed floodplains, for example, in the Mississippi River valley in the states of Louisiana and Arkansas, as a result of the breakthrough of meander necks and channel processes, oxbow lakes are separated in the form of large meanders.
Aeolian processes. In basins of aeolian origin there are lakes dammed by aeolian sands or enclosed among dunes. There are also deflationary lakes associated with deflation basins, which are common in arid or semiarid regions of Texas, South Africa and Australia. The origin of deflation lakes, sometimes called playas, is not fully understood, but they may sometimes form through the combined action of wind blowing and excavation by animals that use them for watering.
Coastal processes. When the sediment flow moves along the coast, 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 most famous lakes formed by such processes. Although its basin arose when a depression was raised at the bottom of the sea, initially the lake. Okeechobee was dammed by dense aquatic vegetation and an accumulation of its remains. Damping of watercourses 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. With 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 bauxite deposits.
Impact of meteorites. Probably the rarest and most unusual lake basins are depressions formed as a result of meteorite impacts. It has been reliably established that one of the lakes on the Ungava Peninsula in the province. Quebec (Canada) dedicated to meteorite crater Nouveau Quebec. This round lake is located among lakes of glacial origin that have an irregular shape.
SOURCES OF LAKE WATERS
To be called a lake basin, a basin formed by one of the methods described above must, of course, at least occasionally be filled with water, which can enter the lake in various ways. In many large lakes in humid regions, a significant portion of the water can come directly from precipitation falling on the surface of the lakes. For example, food from the lake. Victoria in East Africa is about 75% atmospheric. The main source of water for smaller lakes or lakes in more arid regions is usually the surface runoff of rivers and streams. Lakes can be fed by groundwater emerging from the underwater part of the lake basin. Many lakes, in particular those of glacial origin, are confined to basins excavated in layers of loose aquiferous sediments and are located below the groundwater level. In this case, water enters or flows out of the lake, seeping through the sides of the basin. There are also key lakes that are at least partially fed by underwater springs. Sometimes it comes from sources into the lake. great amount salts captured when a watercourse passes through easily soluble rocks (for example, in Lake Tiberias). The freshest waters are typical for lakes fed exclusively by 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 feeding stream. Lakes, in the basins of which water filters both into and out of the lake, are usually fresh. However, some lakes have an influx of water, but no outflow, and the water only evaporates from their surface, as a result of which the concentration of soluble salts in the reservoirs increases. In such endorheic or “closed” lakes (as opposed to “open”), highly specialized communities of plants and animals, such as certain crustaceans or insects, often form. Another factor influencing the salinity of lakes is the amount of precipitation. Finally, character is important rocks, among which there are lakes. Thus, lakes in the Canadian Shield region are mostly very fresh, since the rocks through which 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 change of water in the lake (in years), which is expressed through the ratio of the volume of the lake to the annual flow of water from it, or through the inverse value called the water exchange coefficient of the reservoir. The time for a complete change of water 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 Verkhny). Reservoirs 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 WATERS
Water is an excellent solvent, and therefore lake waters contain many dissolved substances. It is noteworthy, however, that the overwhelming mass of these substances in most lakes is 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 account for 90 to 95% of the total dissolved solids in most lake waters, and their total concentration, usually measured in milligrams per liter (mg/L), measures the salinity (salinity) of the water. Other substances, such as plant nutrients (nitrogen and phosphorus) and metals (iron and manganese), are present in much smaller quantities, so their concentrations are measured in micrograms per liter (µg/l). In closed lakes, evaporation leads to a change in the composition of salts. Lakes are called chloride, sulfate or carbonate depending on which anions have accumulated in them in the greatest quantities under the influence of evaporation or precipitation.

STRATIFICATION OF LAKE WATERS
In some lakes, especially those that are shallow or exposed to strong winds, there is no noticeable stratification of the water at all. This means that the water masses are more or less constantly mixed by the wind and are fairly uniform in all respects. However, most deep lakes and those located in the wind shadow are characterized by a clear stratification of the water column according to physical properties, as a result of which less dense waters are located above denser ones. This 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 with both increasing and decreasing temperatures. In lakes, sunlight is used by plants for photosynthesis and by animals to see underwater. Light also affects the vertical migrations of some organisms, but the main result of exposure to solar energy is heating of water. The influx of energy from the Sun is significant. Arrival of solar energy within one summer day can reach 500 cal per 1 cm2 of lake surface. Part of this energy is reflected from the lake mirror, 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 top few meters of water that heats up, as 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 the density of the underlying cold layers. The heated water accumulates on top of the cold and therefore denser waters. However in early spring , especially in temperate regions, the temperature of the water generally remains low, so that the decrease in density due to such heating is negligible, and the wind mixes the heated water throughout its thickness. Later, as the arrival of solar energy increases, the temperature of the water 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 surface layer of water increases. Ultimately, the wind is no longer able to mix the entire water mass, and the arrival of solar energy is concentrated in the top few meters of water. As a result, 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 a metalimnion, or thermocline. This stratification is determined more by the density of the water than by its temperature. Because in tropical regions, where water temperatures are generally higher, changes in density are much greater (see graph), and the temperature difference between the epilimnion and hypolimnion can be much smaller than in temperate regions. In any case, if the water density in the epilimnion and hypolimnion differs by an amount from 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, becomes denser and soon, together with the underlying waters, is subject to wind mixing, due to which the power of the epilimnion increases. This process continues until the temperature of the water throughout the depth of the lake, as a result of mixing, is equal to the temperature of the hypolimnion or becomes close to it. In tropical areas, where temperatures are constantly above 0 ° C, this kind of circulation of lake waters can continue throughout the winter. However, where winter air temperatures fall below 0° C, lake waters continue to cool and mix until a temperature reaches 4° C. If the surface waters subsequently cool below this temperature, corresponding to the maximum density of the water, they become lighter again and remain on the surface, creating stratification in the lake, which not only depends on density, but is also inversely related to temperature. The binding of ice to the water surface has a stabilizing effect, and this stratification persists throughout the winter until complete mixing of lake waters occurs again in the spring. Thus, the annual cycle of lakes usually includes periods of summer and winter stratification and spring and autumn mixing of lake waters. In most lakes, depending on climatic features 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 remains constant, usually because the density of deep waters increases not due to temperature differences, but rather due to higher concentrations of dissolved chemical compounds. Such lakes, in contrast to those that are periodically completely mixed, are called partially mixed, 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 accumulate 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 Lakes. For example, lake Michigan annually absorbs and then releases 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 the largest lakes, such 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). However, under the influence of temperature gradients, inflowing watercourses and winds, water moves in lakes. For example, at the end of summer, when heat is released from the surface of lakes into the atmosphere at night, the water, thus cooling, 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 the fall. 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 inflow waters have a lower density than the waters of the lake itself, as, for example, in the summer when the Jordan River flows into Lake Tiberias. Mid-depth currents are formed if a watercourse rushes down to layers corresponding to its own density. If there is a simultaneous flow of water through a dam, this flow can travel over long distances and carry water with specific properties (for example, higher or lower silt content) throughout the entire reservoir. If the density of a stream 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, it is even possible to form an underwater channel, as, for example, at the confluence of the river. Rhone to Lake Geneva. Under the influence of wind, several types of movements of lake waters occur. One of them - the vortex wind current (or Langmuir circulation) - is clearly visible on the surface of the lakes by alternating smooth and stripes covered with small ripples. 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, while in others it moves counterclockwise. As a result, longitudinal (stretched along the wind) zones of convergence (counter and downward movement of water) are formed, alternating with longitudinal zones of divergence (ascending and divergent movement of water). Divergence zones are located at a certain distance from one another (for example, from 5 to 15 m). They are easily recognized as smooth streaks because bubbles, dust and other floaters collect along convergence zones where water sinks but is not moving fast enough to carry the material along with it. Another type of water movement occurs when wind constantly blows over the surface of a lake. As 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 shore if the lake is shallow, or, in deeper lakes, in the opposite direction 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 is formed on the surface of the lake, and the water moves first in one direction, then in the other, until these fluctuations die out. Such surface movements of water with alternating directions are called surface seiches. On large lakes their height can exceed several meters. Seiches can cause enormous damage to low-lying coastal areas. Fortunately, such seiches die out quite quickly, and the lakes return to their normal state. If the lake is very deep or has clear stratification, another type of water movement called internal seiches may occur. When water moves with the wind, its level rises by approximately 1 mm for every linear kilometer. If the wind is stable, then the balance of the water mass is disturbed. Both at the surge and surge shores of the lake, warm, less dense water masses are located above the cold and more dense ones, but at the surge shore the layer of water is several millimeters larger. To balance the excess pressure created by this additional layer of water, the denser bottom waters move upwind to the opposite side of the lake, while the less dense surface waters move downwind. This leads to a skew of the thermocline: on the leeward side of the lake it rises. However, since the difference in density 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 shift exceeds the magnitude of the surge by about 1000 times. Therefore, the skew of the thermocline is very large compared to the magnitude of the surge: on large lakes such as Baikal, it can reach or exceed 150 m. When the wind stops, surface seiches quickly level the water level, but the lake again finds itself in a non-equilibrium state due to the skew of the thermocline . As a result, the surface and bottom waters continue their oscillations, and the thermocline, like a pendulum, changes its inclination first in one direction and then in the other, until finally this movement dies out and the lake reaches a state of internal equilibrium. The duration of such oscillations is determined by the parameters of the lake basin, but it is much longer than the period of attenuation 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 minor vertical mixing occurs, but the water is transported over long distances horizontally and can even come into contact with bottom sediments and change its chemical properties. In addition, such movements contribute to the transfer of pollutants discharged into the upper part of the bottom layer of water at one shore of the lake, many kilometers to another place, where water may be withdrawn for industrial or domestic needs. Under some conditions, internal seiches can even cause deep water with very low dissolved oxygen to reach the surface of the lake near the shore, where it causes fish kills. This phenomenon is periodically observed in Lake Tiberias with a characteristic 24-hour period of internal seiches, coinciding with the daily periodicity of summer winds.
LIFE OF THE LAKES
Lakes are home to a wide variety of living organisms, from viruses and bacteria to freshwater seals and sharks. These organisms are not only exposed to 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 contact zone between the atmosphere and water, the contact zone 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.
Contact zone between 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 between bottom sediments and water. The set 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 plants or macrophytes, live in shallow waters where light is available to them and form a distinct zonation. Semi-submerged macrophytes including sedges and cattails grow on the bottom along the edge of the lake. Further from the shore and somewhat deeper, macrophytes take root, such as water lilies with long stems topped with floating leaves, through which carbon dioxide is absorbed from the atmosphere. Even further from the coast, on greater depth macrophytes (for example, pondweed) grow completely submerged in water. In North America, this group includes many species, including curly pondweed (Potamogeton scirpus), urut (Myriophyllum exalbescens), etc. Most of these plants (though not all) 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: what proportion of the lake area is shallow, the properties of bottom sediments and the characteristics of wave activity. While in some lakes with steep underwater slopes (for example, in Upper) there are almost no macrophytes, in many smaller lakes 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 such as Eichhornia and Pistia are common, and in temperate latitudes - tiny duckweed (Lemna). These plants, especially larger ones, can grow strongly and form a dense continuous cover on lakes and reservoirs. The vast surface area of shallow water plants provides 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-water (littoral) areas also provide shelter for various animal organisms - gastropods and bivalves, leeches, insect larvae that live among plants and stones, often found in the coastal zone. Deeper, beyond the littoral zone, macrophytes do not grow. There is a sublittoral zone here, where the bottom gradually drops towards the deep part of the lake. The sublittoral zone is inhabited by bacteria, protozoa and true worms, as well as larvae similar to them 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 a watercourse. Both terms have Greek roots: nektos - floating and plankton - wandering.
Nekton. Based on feeding habits, lake fish are divided into several groups. Piscivorous or predatory fish, which are often classified as non-commercial species, feed mainly on smaller fish and the fry of other fish species. Planktivorous fish feed on plankton suspended in the water column and are themselves often eaten by predatory fish. There are fish that feed on algae and herbivorous fish, such as carp, that feed on plants in shallow waters. Benthic-eating fish eat animals that live at the bottom of reservoirs and organic particles that fall to the bottom of the lake.
Plankton. The term "plankton", originally introduced to designate organisms (plants and animals) passively floating in the upper part of the ocean waters, is also used for organisms living in lakes. There are phytoplankton (plant organisms) and zooplankton (animal organisms). They are all 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 divisions of the plant kingdom. Chloroplasts (specific intracellular formations) of green algae contain the green pigment chlorophyll, not masked by other pigments. In diatoms, chlorophyll is accompanied by other pigments, which 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 predominance of one or another is seasonal nature. For example, in temperate regions, diatoms are most abundant in the spring, followed by green algae in late spring, blue-green algae in the summer, and diatoms again in the fall. In the same climatic conditions in nutrient-rich lakes, blue-green algae dominate much of the year, as is often the case in the tropics. Flagellates, like some blue-green algae, are often present under the ice in winter. The reasons for the successive changes in types of algae throughout the year and the predominance of some of them over others are different. There are numerous conflicting theories to explain these phenomena. In some lakes, up to 200 species of algae can be detected simultaneously at concentrations reaching hundreds of thousands of cells in 1 ml of water. The spring maximum concentration of diatoms is often called the spring bloom of water bodies, and the autumn maximum, accordingly, the autumn bloom. An important property of diatoms is that they use silica (SiO2) to build a hard shell called a shell around the cell. 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 because they, together with larger plants, form the first link in the food chain of water bodies. During the process of photosynthesis, they, using sunlight captured by chlorophyll and other pigments, extract approximately 18-20 elements from lake water and use them in the construction of new cellular substance. At the same time, dissolved oxygen is released in the surface layer of water where photosynthesis occurs. The energy thus accumulated in primary production is then used for the life of other organisms living in the lake. Zooplankton usually refers to 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 (non-disease-causing) bacteria are not animals, they are included in zooplankton. They are abundant in lake water, where their concentration can exceed 100 million in 1 ml. If it were not for these bacteria (many of which decompose organic matter into its constituent parts), metabolism in lakes would slow down and eventually cease, 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 close the cycle, again making these elements available for photosynthesis and growth. Protozoa are microscopic single-celled animals, sometimes called acellular animals, such as amoebas and paramecia (ciliated ciliates). They are often found in abundance in lake waters. Some of them attach to larger organisms, others float freely in the water, feeding on bacteria or tiny organic remains - detritus. Rotifers, named for the corolla of hairs, or cilia, around the mouth opening have a more complex structure than the protozoa. These cilia vibrate harmoniously in such a way that they create the impression of a spinning wheel. Rotifers are multicellular animals. They feed on small algae, bacteria and organic detritus, and sometimes on other rotifers. In most cases, their reproduction is sexual, involving both female and male individuals. 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 the haploid eggs, and special so-called eggs are formed. resting (latent) eggs that have increased resistance to harsh conditions, such as drying out. When environmental conditions become favorable again, females develop from resting eggs and reproduce parthenogenetically. Tiny crustaceans are one of the most visible components of zooplankton. These crustaceans are very small - 0.3-12 mm long. In most lakes, they are the main link between the primary producers (algae) and subsequent links in the food chain (fish). They are so small that they feed only on microscopic algae, but are large enough to become food for fish. Thus, the abundance of these crustaceans is controlled by two factors: food availability and predators. First of all, the 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 visible head, chest and abdomen, ending with a tail. Individual groups of 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, with approximately equal numbers of males and females being born. The eggs are transferred 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 acquire the appearance of adults. Copepods can be recognized by their characteristic galloping swimming pattern. Copepods include Cyclops, which, like its mythological namesake, has a single eye in the middle of its “forehead.” The body of cladoceran crustaceans is enclosed in a translucent, bi-valve chitinous carapace (shell). Most cladocera are herbivorous. They filter the water using 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. The filtered food moves through a special groove to the mouth and enters the intestine, where digestion occurs. The eggs are transferred and develop in a brood chamber located on the female's back. The young leave her during molting. Cladocerans generally 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, which are shed during molting and are able to survive unfavorable periods, and when conditions improve, they hatch into females that reproduce parthenogenetically. Sometimes, under the influence of wind, massive accumulations of such shells form along the edge of the coast. Zooplankton also contains other organisms, such as Mysis, a small crustacean that often lives in the lower, cold, oxygen-rich water layers of deep lakes, and the transparent mosquito larva, which 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 lake chemistry is important to all organisms, as evidenced, for example, by the specialized species of plants and animals that live in salt lakes, it is plants that carry out photosynthesis that have the greatest influence on the chemistry of lake waters. During photosynthesis solar energy used to convert carbon dioxide and water into hydrocarbons and oxygen. Moreover, in addition to carbon dioxide and water, another 18-20 chemical elements are involved in photosynthesis, and reducing the content of any of them below the optimal requirement significantly slows down the process of photosynthesis. This so-called hypothesis of the limiting role of nutrients, put forward in the mid-19th century. Justus Liebig, is still used to characterize aquatic ecosystems. In freshwater bodies, most nutrients are present in quantities greater than required, but two of them - nitrogen and phosphorus - are relatively rare. It is these elements, separately or together, that limit the process of photosynthesis, or primary production. Moreover, since some blue-green algae are able to fix 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 significant characteristics of lakes, such as the total increase in primary production or the abundance of algae, are directly dependent on the phosphorus content in the lakes. Therefore, lakes are classified according to this indicator. There are oligotrophic lakes (with a low content of nutrients), mesotrophic lakes (with an average content) and eutrophic lakes (with a high content of nutrients). The 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 water circulation. At the same time, all other elements necessary for photosynthesis and growth are extracted from the water by algae, and the chemistry of the epilimnion waters undergoes corresponding changes. At the same time, the epilimnion produces a lot of organic detritus, consisting of dead fragments of algae, which sinks into the hypolimnion. There, dissolved oxygen is spent on respiration and decomposition, and many inorganic substances are returned to the water. Thus, in a stratified lake, the initially homogeneous water mass is divided into two clearly distinct layers: the upper, warmer, with a deficiency of available nutrients, and the lower, colder, with a higher concentration of nutrients. In temperate climates, this separation occurs in both 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 entire water column. In many nutrient-rich lakes, photosynthesis occurs so intensely that dissolved oxygen is completely consumed immediately at the surface of the 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, resulting in large amounts of iron, manganese, phosphorus and nitrogen entering the water. This process is called internal eutrophication, since in some lakes, as a result of wind mixing or the influence of internal seiches, nutrients released from sediments enter the upper layer of water, thus increasing the trophic level of the lake. In areas of temperate climate, during the period of spring and autumn mixing of waters, the surface layer of sediment again absorbs oxygen, all differences in the chemical composition of water in depth disappear, and the water mass again becomes chemically homogeneous.
LAKE SEDIMENTS
Lacustrine sediments, which play an important role in the chemistry of lakes, are mostly formed in the lakes themselves. They usually consist of semi-decomposed remains of algae, zooplankton and larger organisms, and in lakes that formed about 10 thousand years ago they can reach great thickness (about 20 m). The study of lake sediment columns 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 seen in the concentrations of various chemicals, such as phosphorus and ammonium. Because lake sediments are typically cold and oxygen-poor, they provide excellent evidence of the lake's past conditions, reflected either in the composition and quantity of specific algal pigments or in the identifiable remains of the most resistant parts of organisms. Various methods have been developed to determine the age of individual layers of lake sediments. Among them are methods based on the use of natural radioactive isotopes of lead 210Pb and carbon 14C; Correlating marker horizons in sediments, such as ash, with historical records of nearby volcanic eruptions. The study of sediments allows us to recreate a detailed picture of changing conditions in a given lake. In addition, since lake sediments accumulate information about the natural conditions of the entire drainage basin, they also record past climate changes. For example, studying the composition of plant pollen in a column of lake sediments makes it possible to determine which terrestrial plants were common at certain stages of geological history, and taking into account the modern environmental requirements of these plant species allows us to determine what the temperatures and humidity were at that time.
PROBLEMS OF LAKE CONDITION
Lakes are ecosystems in which all components are interconnected. In the absence of external influences, lakes reach a certain state of equilibrium with the environment, which over time leads to a more or less stable situation when the organisms living in the lakes adapt to existing conditions. However, lakes are rarely in an equilibrium state. On the contrary, they are often used as sources of water for irrigation, drinking water, for agricultural purposes, or for the discharge of products of modern civilization such as industrial wastewater, storm water and agricultural runoff. The lakes are being polluted by increasing amounts of pesticides, herbicides and airborne organic compounds such as polychlorinated biphenyls, as well as acid rain from pollutants released from automobile engines and thermal power plants. They are penetrated by alien species of plants and animals, brought in by fishermen on the bottoms of ships and in other random ways. Eutrophication, or excessive enrichment of lakes with nutrients from anthropogenic sources, is becoming alarming, causing significant environmental damage. In some cases, large, economically important lakes are even in danger of disappearing completely. For example, the volume of water in the Aral Sea (a large salt lake) has now been halved due to the diversion of water from the Amu Darya and Syr Darya flowing into it for irrigation. As a result, its salinity increased almost threefold (from 9.6-10.3‰ to 27-30‰). Exposed areas of the seabed are blown by dust storms, which leads to the removal of salts and pesticides and their deposition within nearby populated areas. Lake pollution is a very serious problem. For example, to reduce the eutrophication of water bodies, many countries have adopted laws to limit the concentration of phosphorus in waters that pass through treatment plants and that can end up in lakes. A whole science of lake restoration has emerged, based largely on empirical relationships linking indicators such as algae abundance and water clarity to phosphorus concentrations in lake waters. In some regions, water withdrawal 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 (Kazakhstan - Uzbekistan), salty 36.5* Tanganyika (DRC, Burundi, Tanzania, Zambia) 32.9 Baikal (Russia) 31.5 Great 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), salted 22.0* Ontario (USA - Canada) 19.7 Ladoga (Russia) 17, 7 Chad (Niger, Chad, Cameroon, Nigeria), salty 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 Deer (Canada) 6.7 Rudolph (Kenya - Ethiopia), salted 6.5 Issyk-Kul (Kyrgyzstan), salty 6.2 Kokunor (Qinghai) (China), salty 5.7* Torrens (Australia), salty 5.7* Vänern (Sweden) 5.7 Albert (DRC - Uganda) 5.6 Nettilling (Canada) 5.4 Winnipegosis (Canada) 5.39 Kariba (Zambia - Zimbabwe) 5.31 Nipigon (Canada) 4.9 Gairdner (Australia), salted 4.77* Urmia (Iran), salted 4.69 Manitoba (Canada) 4.66 Forest (USA - Canada ) 4.47 *Area is not constant.
LITERATURE
Bogoslovsky B.B. Lake science. M., 1960 Muraveysky S.D. Rivers and lakes. M., 1960

Collier's Encyclopedia. - Open Society. 2000 .

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