Lakes of the world. Unusual lake. Lakes of the world
Lakes, formed from river oxbow lakes, are relatively small. Large arose in other ways. Some in valleys, blocked by avalanche or moraines, rock ridges left by retreating and now-vanished glaciers or dams erected by man. Lake Baikal in Siberia and lake in East Africa filled the huge cracks in the earth’s crust, caused by powerful shifts. American Great lakes lie in the basin, formed during the ice age when the ice wore a large part of the continent. Glaciers not only plowed a deep bowl in the valleys, along which, but this entire region sank under the weight of ice, gavluvsga a lot of the continent in plastic basalt layers under it. Then the ice melted relatively quickly, but the concavity is not yet corrected.
Around the perimeter of the great lakes in shallow bays among marsh grasses the animals and their lifestyles are not much different from what we observed in a small freshwater reservoirs. Over them worn different dragonflies, among the plants reproduce gnats and mosquitoes; hiding in the mud snails and bivalves; fish and piranhas hunt, carp and Cichlidae pluck the plants. But where the lake bottom out to a great depth, the conditions have dramatically changed.
Baikal is the deepest lake in the world. In some places the bottom is a mile from the surface. Of course, compared to the ocean it’s not much of depth, but in ocean bottom currents in the closed world of great freshwater lakes they invade rarely. Flowing into lakes rivers carry relatively warm water, and she stays on top of cold water at depth. Sometimes a strong storm can to some extent mix the upper layers of the raging water with those that are under them, but usually water in the depths of the great lake at a temperature close to the freezing point, black, oxygen-poor and contrary to all the legends about living in the lakes these monsters mostly lifeless.
And yet these lakes are inherent biological peculiarity. Community of animals, once established in these isolated aquatic realms, with little or no replenishment from the outside. A wandering inhabitant of the waters may enter the lake by travelling the river. But to get to it — most often means to swim against the current, to overcome the smaller lakes and waterfalls. Few of us ever do, and most of the inhabitants of the great lakes comes from species that lived near their origins. Minor genetic changes in some individuals in these close communities is not lost, as usually happens in large populations, it is easier and saved. Therefore, in lakes often develop their views, which are nowhere else to be found.
Lake Tanganyika about one and a half million years, and it found 130 species of cichlids and 50 species of other fish, is now completely unique. Like many of his crustaceans and molluscs. The inhabitants of lake Baikal, perhaps, even more remarkable. It is home to 1200 species of animals and 500 species of plants, over 80% of which are found only in him. Large flat worms, red and orange, stripes and spots; fish living on the bottom kilometre underground, and shellfish, whose shell is a lot thinner than their marine relatives, since lake water is less rich in calcium salts than sea.
Baikal has its unique mammal is a freshwater seal. It is very similar to ringed seal living in the Arctic, and almost certainly occurred from it. But between the Baikal and Arctic ocean — more than two thousand kilometers, and on the river path so many rapids and waterfalls that beat them not under force to any seal. It is possible, however, that the seal climbed into the lake by rivers during the ice age, when this trip was supposed to be a lot easier and a lot shorter. Modern Baikal seal not only the only member of his family living in fresh water, but noticeably inferior to all other dimensions.
In geological scale of the lake — a very fleeting ornaments of the earth’s surface. Oxbow lake may disappear in several decades. More lakes can survive for thousands of years, but they are reduced. The river, flowing into quiet lake, thrown into the mouth load of sediment, forming a Delta that gradually invade the lake, causing it to dry out. Near the banks it is shallow because the streams there demolishing the soil from the surrounding heights. The bottom rises toward the light, and aquatic plants spread further and further, polluting the water with their stems, rotting leaves and roots. So the lake becomes a swamp, and it is, drying up, in turn becomes a fertile meadow, which was still a river winding, the first choking the lake.