2.12.2010.Zavershilsya field season at the Laboratory of Aquatic Ecology Ilmen Reserve. Scientific research on the lake Big Miassovo at the center of the reserve, identify the causes of unusual events that take place there.
A few years ago, scientists noticed a strange reduction of oxygen in the lake water. Oxygen depletion in the water column below the thermocline boundary (called the thermocline) — common in many South Ural lakes where summer is temperature stratification (stratification) of the water column.
The reason for the deficit — biochemical oxygen demand of the bottom layers of the oxidation of organic matter sediments. The temperature stratification prevents vertical mixing of lake waters and does not allow oxygen to penetrate in sufficient quantity from the surface to the depth of the lake through the thermocline zone.
Because of this, the oxygen content of the summer in the lower layers of stratified lakes water is always below the saturation threshold, and usually ranges from 20-40%, sometimes dropping to 2-5% and even up to zero at the bottom. In the anaerobic (oxygen-free) fermentation of sludge thickness frequently granted hydrogen sulfide. These phenomena in the lake Big Miassovo would not present anything unusual, if not for their amazing proportions.
Recent studies have shown that at a depth of 8-10 m (just below the thermocline zone) of oxygen is rapidly reduced to 10-20%, and even a little deeper analytical drops to zero. This is recorded in all the deep water of the lake. In this case, at a depth of 10-12 m water saturated with hydrogen sulfide to give off a strong characteristic smell. Given that much of the lake has a depth of about 22-25 meters, you can say that about two thirds of the water column of the lake is almost devoid of oxygen. Such a lack of it is quite impossible to explain the biochemical consumption for the oxidation of organic matter, simply because of the substance in the lake in an amount not.
Abundance and biomass of plankton (the main supplier of organic matter in sediments) in the Grand Miassovo small, insignificant thickness of silt, and many sections of the sea they do not have. It was assumed that the oxygen is consumed in a purely chemical oxidation of some solutions to Lakes of the rocks composing the bottom of the lake basin. Moreover, this process has become intense recently, about 3-5 years ago.
Perhaps, at the bottom of the lake formed fissures through which the water began to come in a lot of substance, and the oxidation which consumes much of the oxygen dissolved in water. Since Lake Big Miassovo once emerged along the meridional fault current flowing in the western part of the region and was conducted echo-shooting bottom. Some of the most deep water (24-25 m) were found echograms breaks, which can be explained by the presence in these places is very narrow (5-15 cm) and very deep cracks, floor beam sonar which could not be achieved.
According to the head of the biological department k.b.n Alexander Rogozin, this was not only able to confirm the presence of modern tectonic processes in Ilmen mountains, but also allows you to formally assume Lake Big Miassovo one of the deepest lakes in the Urals.
Press service of the Ilmen Reserve