Lakes with unique salinity. Classification of lakes and their origin Which lakes are fresh and which are salty

In natural waters there are always impurities in the form of suspended or dissolved substances, and they can be considered as a very complex solution, representing a true solution in relation to some substances, and colloidal in relation to others.

With the help of special methods of filtration from natural waters, it is possible to isolate the colloidal part, separating it from water and electrolytes. In this way, for example, it was established that in the entire water mass of Lake Baikal there are about 55 thousand tons of solid matter in a finely divided phase. In general, in the hydrosphere (on the whole Earth), the order of concentration of colloids is expressed by the value x · 10 -5%, where x does not exceed the order of hundreds.

However, water is of particular interest as a true solution, because the concentration of molecularly dissolved substances is immeasurably more significant than the concentration of colloids.

Any water contains certain salts in solution, but if the salinity of the water is less than 0.3‰, then such water is called fresh water. Therefore, in 1 thousand g fresh water contains less than 0.3 g of dissolved salts. When the salinity is from 0.3 to 24.695‰, the water is called brackish, and when the salinity is above 24.695‰, it is called salty. The value of 24.695‰ was chosen as a boundary between brackish and saline waters because only at this salinity value, the freezing point of water and its highest density are equal (-1.332°). If the salinity is less than 24.695‰, then with continuous cooling, the water will first reach its highest density, and then it will freeze; if the salinity is more than 24.695‰, then water under similar conditions will freeze before it reaches its highest density.

For obvious reasons, in flowing waters it is difficult to expect high concentration salts. But in stagnant reservoirs, especially those deprived of runoff and subjected to increased evaporation, a lot of salts accumulate. In accordance with this, lakes are divided into fresh and salt, or mineral.

in the lakes marine origin, i.e., in reservoirs separated from the sea, the presence of salts in the water is, as it were, a "hereditary" phenomenon. In the process of further independent existence of such a relict lake, its hereditary features either increase (it becomes more salty than the parent lake). water basin), or weaken (desalination). As for continental salt lakes, salts enter them due to chemical weathering of crystalline rocks, leaching of various sedimentary rocks, dissolution of ancient salt deposits by groundwater, etc.

The main factors in the distribution of mineral lakes are the climate and the presence of drainage basins, as well as the composition of the rocks that make up the area, and the groundwater regime. Steppes and deserts are the birthplace of salt lakes, since there is little precipitation, evaporation is high, and the relief is predominantly flat, and therefore the runoff is weak. The large lakes of Tibet - Namtso (Tengri-Nur), Kukunor, and others - are salt lakes.

But salt lakes can also be in a humid climate if there are salt deposits nearby; in this case, the origin of the salt lake is influenced not by the modern climate, but by the climate of the geological past, in which salt deposits could form. Thus, the small salt lakes of the Leno-Vilyui Plain are fed by salt springs that come out of the salt-bearing strata of Paleozoic rocks.

Mineral lakes are quite diverse in terms of the composition of dissolved salts. Soda lakes are widely represented in Western Siberia (Lake Tanatar, Petukhovskie lakes, etc.), in Transbaikalia (Lake Doroninskoe), and Yakutia. Bitter-salty, or sulfate lakes, which precipitate mainly Glauber's salt, are found in the Kulunda steppe, in the Crimea, in the Caucasus (Batalpashinsky lakes), in the deserts of Central Asia, etc. Salt (chloride) lakes are among the most common - their many in the Crimea, in the Kulunda steppe in the Volga region and other places. The Kulunda steppe, in terms of the number of mineral lakes (there are several thousand of them here) and their diversity (soda, salt, Glauber lakes), is undoubtedly an area for the development of a large chemical industry in the future.

The concentration of salts in mineral lakes varies over a very wide range. It differs not only in different lakes, reaching up to 37% in some cases, but often changes noticeably in the same lake depending on the water level in the latter, i.e., depending on the volume of the water mass. Thus, the salinity of the Great Salt Lake in Utah, in accordance with fluctuations in the water level in the lake, varies from 13 to 22%.

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Terrestrial reservoirs arose for various reasons. Their creators are water, wind, glaciers, tectonic forces. The water washed out the hollow on the surface of the earth, the wind blew out a depression, plowed and polished the glacier depression, the mountain landslide dammed the river valley - and the bed of the future reservoir is ready. The depressions will be filled with water - a lake will appear.

The lakes of the globe are divided into two large groups - fresh and salt water. If less than one gram of salts is dissolved in one liter of water, the water is considered fresh, if there are more salts, then salty.

The lakes have the most varied salinity - from fractions of a gram to several tens and hundreds of grams per liter of water. There are, for example, reservoirs in which the water is so saturated with salts that it surpasses the ocean in this respect (35 grams of salts per liter of water); such lakes are called mineral. It all depends on what kind of tribute the rivers bring to them. If the climate is humid and the rivers are full of water, then the rocks in the catchment area are well washed, and therefore the river and lake waters are poorly mineralized.

In a drier climate, where precipitation is scarce and rivers are shallow, their waters contain significantly more salts. Therefore, in the deserts, salt (mineral) lakes are the most widespread. A vivid example of this is Central Kazakhstan, where there are few freshwater lakes, and salty ones are found almost at every step. And yet, among the greatest lakes in the world, freshwater reservoirs predominate.

They are flowing, water does not stagnate in them, salts brought by rivers are discharged into the ocean or sea. And it is worth making such a reservoir drainless - and after some time it will become salty. Take, for example, the Caspian Sea. This huge body of water became largely saline because it had no outlet to the ocean. There were many similar cases on Earth.

The most saline lakes on our planet can be considered lakes in which the salt content per liter of water is more than 25 grams. Such lakes, in addition to Lake Tuz in Turkey, include Lake Eyre in Australia, the Dead Sea on the Arabian Peninsula, Molla-Kara in Turkmenistan, Lake Dus-Khol in Tuva and others.

In the center of Turkey, south of Ankara, at an altitude of 900 meters above sea level, there is a lake on which you can walk on foot in summer. This drainless Lake Tuz is 80 kilometers long, about forty-five kilometers wide and average depth- two meters. It is not only shallow, but also very salty - up to three hundred and twenty-two kilograms of salt per ton of water. In spring, due to winter and spring precipitation, the lake overflows and increases almost seven times, occupying a huge area of 25,000 square kilometers. In the summer, when the water evaporates, the lake becomes very small, and a dense crust of salt forms on its surface from several centimeters to two meters thick.

The Dead Sea is the deepest and saltiest of the salt lakes. Its greatest depth is over 400 meters, and it is located 395 meters below the level of the oceans. One liter of water Dead Sea it contains 437 grams of salt.

Some of the lakes are brackish-fresh. The most amazing of them is Lake Balkhash. Its western part is fresh, and the eastern part is brackish. The reason for this peculiarity lies in the fact that the Ili River flows into the western part of the lake, and the eastern part lies surrounded by deserts, where water evaporates very strongly. Therefore, on geographical maps the western part of Balkhash is shown in blue, and the eastern part in lilac.

The huge Lake Chad, located on the outskirts of the Sahara, is fresh on top and brackish at the bottom. Fresh river and rain water, falling into the lake, does not mix with brackish water, but rather floats on it. Freshwater fish live in the upper layer, and marine fish that got into the lake in ancient times stay at the bottom.

The lake is very shallow (from 2 to 4 meters deep). Its shores are flat and swampy, and from the north the desert comes close to them. The hot sun dried up all the northern and eastern tributaries of Chad, turning them into waterless channels - wadis. And only the Shari and Lagoni rivers flowing into it from the south feed the "Sahara Sea" with their waters. For a long time, Lake Chad, or Ngi-Bul, as the locals call it, was considered drainless, which was its essence. main riddle. Usually in large, shallow and endorheic lakes on Earth, the water is completely salty, and the upper layer of Lake Chad is fresh. The riddle turned out to be simple.

Approximately 900 kilometers northeast of Chad is the vast Bodele Basin, lying approximately 80 meters below lake level. A water stream hidden under the ground stretched to it from the lake. So, through underground runoff, Lake Chad slowly but constantly renews its waters, preventing them from becoming salty.

Even more surprising is Lake Mogilnoye. It is located on Kildin Island, not far from north coast Kola Peninsula, and has a depth of 17 meters. The lake consists, as it were, of several layers - "floors". The first "floor" at the bottom of the lake, almost lifeless, consists of liquid silt and is saturated with hydrogen sulfide. The second "floor" stands out in cherry color - this color is given to it by purple bacteria. They are, as it were, a filter that traps hydrogen sulfide rising from the bottom. The "third" floor is a "piece of the sea", hidden in the depths of the lake. This is the usual sea water, and its salinity here is the same as in the sea. This layer is filled with life, jellyfish, crustaceans, stars, sea anemones, sea bass, cod live here. Only they look much smaller than their counterparts at sea. The fourth "floor" is intermediate: the water in it is no longer sea, but not fresh either, but slightly brackish. The fifth "floor" is a six-meter layer of pure spring water suitable for drinking. Animal world here common for freshwater lakes.

The unusual structure is explained by the history of the lake. It is very ancient and was formed on the site of the sea bay. Mogilnoye Lake is separated from the sea only by a small bridge. At high tide, sea water seeps through it in the place where the "marine" layer is located. And the distribution of water in the lake by layers is due to the fact that salt water, as heavier, is at the bottom, and lighter fresh water is at the top. That's why they don't mix. Oxygen does not enter the depths of the lake, and the bottom becomes contaminated with hydrogen sulfide.

On geographical maps, the lakes are painted either blue or lilac. Blue color means that the lake is fresh, and lilac - that it is salty.

The salinity of the water in the lakes is different. Some lakes are so saturated with salts that it is impossible to drown in them, and they are called mineral lakes. In others, the water is only slightly salty in taste. The concentration of dissolved substances depends on what kind of water the rivers bring them. If the climate is humid and the rivers are full of water, the lakes are fresh. In deserts, there is little rainfall, rivers often dry up or they don’t exist at all, which is why the lakes are salty.

Among the large lakes of the world, most of all are fresh. This is due to the fact that the water in them is flowing and does not stagnate, which means that the salts brought by the rivers are carried away by them into the seas and oceans.

The freshest lakes on the planet- this is Baikal in Asia, Onega and Ladoga in Eastern Europe, Upper in North America. But the freshest of them should still be considered Lake Benern - the largest of the lakes Western Europe. Its water is the closest to distilled, there are slightly more soluble minerals in Baikal and Lake Onega.

The freshwater lake of the largest area of the water surface - Lake Superior - one of the Great Lakes of North America. Its area is 83,350 square kilometers.

Mountains are especially poor in salts. glacial lakes, whose waters feed glaciers and snowfields.

If the reservoir is not flowing, then the water in it becomes first slightly brackish, and then salty.

In the center of Turkey, south of Ankara, at an altitude of 900 meters above sea level, there is a lake on which you can walk on foot in summer. This drainless lake Tuz has a length of 80 kilometers, a width of about forty-five kilometers and an average depth of two meters. It is not only small, but also very salty - up to three hundred and twenty-two kilograms of salt per ton of water. In spring, due to winter and spring precipitation, the lake overflows and increases almost seven times, occupying a huge area of 25,000 square kilometers. In the summer, when the water evaporates, the lake becomes very small, and a dense crust of salt forms on its surface from several centimeters to two meters thick.

The Dead Sea is the deepest and saltiest of the salt lakes. Its greatest depth is over 400 meters, and it is located 395 meters below the level of the oceans. in one liter waters of the dead sea it contains 437 grams of salt.

Some of the lakes are brackish-fresh. The most amazing of them is Lake Balkhash. Its western part is fresh, and the eastern part is brackish. The reason for this peculiarity lies in the fact that the Ili River flows into the western part of the lake, and the eastern part lies surrounded by deserts, where water evaporates very strongly. Therefore, on geographical maps, the western part of Balkhash is shown blue, and the eastern part is lilac.

The lake is very shallow (from 2 to 4 meters deep). Its shores are flat and swampy, and from the north the desert comes close to them. The hot sun dried up all the northern and eastern tributaries of Chad, turning them into waterless channels - wadis. And only the Shari and Lagoni rivers flowing into it from the south feed the "Sahara Sea" with their waters. For a long time, Lake Chad, or Ngi-Bul, as the locals call it, was considered drainless, which was its main mystery. Usually in large, shallow and endorheic lakes on Earth, the water is completely salty, and the upper layer of Lake Chad is fresh. The riddle turned out to be simple.

Even more surprising is Lake Mogilnoe. It is located on Kildin Island, not far from the northern coast of the Kola Peninsula, and has a depth of 17 meters. The lake consists, as it were, of several layers - "floors". The first "floor" at the bottom of the lake, almost lifeless, consists of liquid silt and is saturated with hydrogen sulfide. The second "floor" stands out in cherry color - this color is given to it by purple bacteria. They are, as it were, a filter that traps hydrogen sulfide rising from the bottom. The "third" floor is a "piece of the sea", hidden in the depths of the lake. This is ordinary sea water, and its salinity here is the same as in the sea. This layer is filled with life, jellyfish, crustaceans, stars, sea anemones, sea bass, cod live here. Only they look much smaller than their counterparts at sea. The fourth "floor" is intermediate: the water in it is no longer sea, but not fresh either, but slightly brackish. The fifth "floor" is a six-meter layer of pure spring water suitable for drinking. The fauna here is typical for freshwater lakes.

An unusual lake called Drutso is located in Tibet. The locals consider it magical. Every 12 years, the water in the lake changes: it becomes either fresh or salty.

We remember: What sources feed the lakes? What is evaporation? Keywords:feeding of lakes, waste and endorheic lakes, fresh and salt lakes.

1. Waste and endorheic lakes. The lakes are fed by river, underground runoff and atmospheric precipitation. Depending on the flow of water, the lakes are sewage and endorheic. Lakes with river flow, that is, from which rivers flow, are s t o c h n e lakes, and lakes that do not have a runoff - b i s s o c t i o n e. Waste lakes are located mainly in areas of excessive moisture, drainless - in areas of insufficient moisture.

The level of lakes in connection with the inflow and outflow of water does not remain constant, it changes. Especially large fluctuations in the level of lakes are observed in arid and dry regions. Changes in the area of lakes are associated with this.

** The Australian Lake Eyre North in the rainy season of wet years is a large body of water up to 9300 km 2, and in the dry seasons of dry years, water is retained only in a few bays in the southern part of the lake.

Fresh and salt lakes. According to the amount of dissolved substances, lakes are divided into fresh(salt content less than 1 g per liter of water), salty(from 1 to 24 g of salts per liter) and salty, or min eral(salt content more than 24 g per liter of water). In lakes with high salinity, salts precipitate. Usually sewage lakes are fresh, as the water in them is constantly updated. Endorheic lakes are most often brackish or salty. This is because evaporation dominates the water flow of such lakes. All minerals brought by rivers and groundwater remain and accumulate in the reservoir.

** One of the largest salt lakes on Earth - the Great Salt Lake in North America (salinity from 137 to 300 0 / 00) (Fig. 131). by the most salt lake world is the Dead Sea - the maximum salinity is 310 ppm.

As a result of sediment deposition and vegetation overgrowth, lakes gradually become shallow, and then turn into swamps. They, like rivers, are the most important natural wealth. Lakes are used for navigation, water supply, fishing, irrigation, recreation, treatment, and obtaining various substances.

1. What are the lakes in terms of water consumption and salinity? 2. Why is the water in endorheic lakes most often brackish or salty 3. Name the most big lake your area. How is it used by the local population?

Practical work.

Divide these lakes into two groups (drainage and drainless): Baikal, Caspian Sea, Ladoga, Onega, Victoria, Tanganyika, Aral Sea, Chad, Air North.

Draw a sewage and drainless lake?

3. Describe on the map one of the world's lakes according to the plan (see Appendix 2).

& 45. Glaciers

We remember: What land waters have we studied? Remember what glaciers are. Name the properties of ice .

Keywords:snow, glaciers, continental and mountain glaciers, moraine

1. Glaciers and their formation. Accumulations of ice on the earth's surface are glaciers. They do not have the ice that covers our rivers and lakes in winter.

* On Earth, glaciers occupy an area of about 16.1 million km 2, which is approximately 11% of the land. Glaciers are found in all latitudes, but the largest area of glaciation occurs in the polar regions.

Glaciers are formed as a result of the accumulation and transformation of solid atmospheric precipitation, mainly snow. If more snow falls than it can melt, it accumulates, compacts and turns into transparent bluish ice.

Rice. 132. Scheme of the structure of the glacier

* The height at which as much snow falls in a year as it melts is called the snow boundary (line). In tropical latitudes, the snow limit is located at an altitude of 5000 - 6000 m and drops to the ocean level in polar latitudes. Below this limit, during the year less snow falls than can melt, and therefore its accumulation is impossible. Higher, due to low temperatures, snowfall exceeds its melting, and snow accumulates and transforms into ice. Here is the feeding area of the glacier. From here, ice, being a plastic substance, flows down in the form of a glacial tongue (Fig. 132).

Glaciers are moving slowly. The speed of movement of glaciers in most mountainous countries is from 20 to 80 cm per day, or 100 to 300 m per year. In the ice sheets of Greenland and Antarctica, the ice moves even more slowly - from 3 to 30 cm per day (10 - 130 m per year).

2. Cover and mountain glaciers. Glaciers are divided into cover and mountain.

C o r o v n e, or ma t e r i k o v e, glaciers occupy the surface of the land, regardless of its relief, which does not affect the shape of the glacier (Fig. 133). They have a plano-convex surface in the form of domes or shields. Ice accumulates in the middle part and slowly spreads to the sides. Glacier tongues often descend to the coastal part of the ocean, as, for example, in Antarctica. In this case, blocks of ice break off from it, turning into floating ice mountains - icebergs (Fig. 134).

Rice. 134. Formation of icebergs

The height of icebergs above the water surface is on average 70 - 100 m, most of them are under water.

** One of the icebergs off the coast of Antarctica was 45 km wide and 170 km long with an ice thickness of more than 200 m.

Icebergs move under the influence of currents and winds to warmer latitudes, where they melt. They are dangerous for navigation. Modern ships are equipped with means of their detection.

Continental ice sheets are developed in Antarctica and Greenland, on the islands of the Arctic Ocean. Ice sheets once extended across most of Europe, northern Asia, and North America.

Rice. 133. Ice sheet of Antarctica

* Continental glaciers occupy 98.5% of the area of modern glaciation. Antarctica is almost completely covered with ice (the area not covered with ice is 5% of the total). The average thickness of the ice cover of Antarctica is 2200 m, the maximum is 4776 m. A powerful ice sheet is carried by the island of Greenland .

Mountain glaciers, unlike coverslips, are smaller and differ in a variety of shapes. The shape of mountain glaciers is determined by relief. Some, like caps, cover the peaks, others are located in bowl-shaped depressions on the slopes, and others fill the mountain valleys (Fig. 135).

Rice. 135. Mountain glaciers

* The most common are valley mountain glaciers that move from feeding areas along mountain valleys down. They can receive tributaries and have icefalls. The thickness of mountain glaciers is usually 200 - 400 m. The world's largest mountain glaciers are the Malaspina glacier in Alaska in North America (100 km long) and the Fedchenko glacier in the Pamirs in Asia (71 km).

3. Significance of glaciers. Glaciers have large reserves of fresh water. They contain many times more water than rivers and lakes combined. Mountain glaciers often feed streams and rivers.

Glaciers, like flowing waters, change the relief of land. During their movement, they develop glacial valleys, expand and deepen them, erase irregularities that impede their movement, demolish loose rocks, transfer and deposit various materials in other places. At the same time, the work of glaciers takes place where there are no rivers - in high-mountainous and polar countries.

Solid material transported and deposited by glaciers is called sea. Moraine consists of sands, sandy loams, loams, clays, gravel, boulders and is deposited during the melting of glaciers. It composes moraine plains, ridges, hills, uplands (Fig. 136).

1. What natural formations are called glaciers? 2. What is a snow border? 3. How do continental (cover) glaciers differ from mountain ones? 4. What is the importance of glaciers? 5*. Show on a pie chart the ratio of continental and mountain glaciers.

& 45. Glaciers

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