Placement of different geochemical types of lakes in the Western Mongolia

Kolpakova M.N., Shvartsev S.L.

National research Tomsk Polytechnic University, Tomsk, Russia

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In our treatment of geochemical information on the composition of salt water lakes in Western Mongolia, it became necessary to organize the geographical patterns of their spatial distribution and to map the schema of geochemical types. This will allow further study the details of object types and compile information related to the processes of formation of lakes of different geochemical types.

The peculiarity of the morphometric and morphological structure of the singularities of the basins children, the height of their location above sea level, geographic, geological and climatic features of the structure of the area and chemical composition of water cause a variety of geochemical distribution of the types of lakes. Location of lakes on the territory of the MPR and their size is largely due to regional characteristics of climate and moisture flow.

The leading factors determining the emergence and development of lake systems vary greatly depending on altitude. In this direction, changing climatic characteristics (radiation, air temperature, precipitation), especially the circulation of groundwater and surface water, a change of some other soil types. Such changes in the components of the environment determine the significant differences in the nature of the geographical distribution of lakes, the conditions of existence, the dynamics of their development [2].

The reliefs of western Mongolia are very diverse. Most of the study area is closed between the Khangai and Mongolian Altai Great Lakes Basin. In the placement of lakes on the territory observed high-altitude zone. For example, the coefficient of compactness lakes varies with the height of their position, which may be associated with the change of relief-forming factor in the transition from the mountain to the plain terms of [2].

At the same time, the distribution of the altitude lakes in the territory of the Mongolia has a number of features. High-altitude range of their distribution from the lower to the upper limit is 3,050 meters tall divided into several levels with the maximum number of lakes at elevations of 1,400 to 2,000 m - about 50% of the studied lakes, from 1000 to 1200 m - 24% of lakes, from 2000 m and above - 15%, and up to 1000m - about 1% of the lakes (Fig. 1). Analysis of the relationship shown in Fig. 2, showed that mineralization of the studied lakes demon waste with a volume of water mass from 0.1 to 66 km 3 from 4 to 20 g / l, and salinity of lakes with water of less than 0.1 km3 of up to 400 g / l or more.

With all the plots on the territory of West Mongolia can be divided into three main areas of distribution of saline lakes of the Mongolian Altai, Khangai and North Gobi (Great Lakes Basin). Mongolian Altai mountain lakes vary in size, height, location and morphology of the basins, and therefore their physical and geochemical properties vary greatly. Salt lakes in the north of the Mongolian Altai there, the most saline salinity does not exceed 3-5 g / l. The largest and typical for the mountainous region of nuclear explosion lakes Achit-Nuur, Tolbo-Nuur, Ureg-Nuur, Dundo-Nuur, Baga-Nuur. Of these, only two brackish lakes (Ureg-Nuur, Baga-Nuur), they are not pre salinity exceeds 4.3 g / l. The rest of the lakes are fresh and ultra-fresh. What can be said about the southern part of the Mongolian Altai, where the highly developed and less chloride sulfate lakes, such as Ihes-Nuur, Tonhil-Nuur, Hulam-Nuur, etc., which the salinity reaches 298 g / l. All of them are fairly small in size (volume of water mass is less than 0.01 km3) and thus more exposed to evaporative concentration of salts.

Khangai mountain region is characterized by a predominance of small and medium-sized lakes, many of which are brackish and salty. Most lakes in this area relates to the type of chloride lakes (Telmen-Nuur, Dzhugnayn-Nuur, Oygon-Nuur, Tsavdan-Nuur).

In the first group of lakes in this region by morphological and morphometric features can be combined lakes Dzhugnayn-Nuur, Holbo-Nuur and Tunamal-Nuur (salinity 2.5 - 4.5 g / l). The average depth of these lakes is less than 25 m deep incision of the basin HN, protected by mountains on the effective impact of the wind. Water balance and level regime of lakes in this group has not been studied. According to reports, along with the evaporation of a significant proportion of the expenditure side of the water balance of these lakes is under terrestrial runoff and infiltration through the sand. A characteristic feature of the regimes of these lakes in recent decades, a trend toward higher levels of water, which is especially pronounced in lakes Bust-Nuur and Dzhugnayn-Nuur in the form of flooding of the coastal forest.

Telmen-Nuur and Sangiyn-Dalai-Nuur - the largest lake Khangai constitute the second subgroup of the small number that is typical for this area. Both lakes are stagnant and brackish pond (7.6 and 4.1 g / l, respectively). Both lakes are deep-water areas with depths of up to 27-30 meters is a few of the Mongolian lakes, for which a first approximation, reduced water balance, which shows that, as in general, for inland lakes in Central Asia, the leading role in their power belongs to the surface runoff, sometimes underground. It is obvious that the current water balance in mountain lakes has undergone a change, given the stability in recent years, the trend of water level increases, which leads to flooding coastal forest on the lake Sangiyn-Dalai-Nuur and terraces on the lake Telmen-Nuur [1].

And finally, in a separate subgroup consists of chloride and lakes Tsavdan-Nuur and Oygon-Nuur, salinity, respectively, which amounts to 340 and 19 g / l. Lake Tsavdan - a relatively small pond of about 5 km2. The depths of the lake did not exceed 0.6-1.0 m [3]. On the lake are mined salt. In the water balance of lakes in the region's leading role in their food belongs to runoff, and the modern course of the levels has a tendency to increase.
Perhaps the most interesting and diverse geochemical characteristics of Gobi is the area of ​​western Mongolia. A variety of physiographic features and climatic factors, which change occurs not only with the seasons, but in the interannual variations of form a variety of geochemical types of lakes. Here are the biggest lakes of Mongolia: Hirgis-Nuur and Uvs-Nuur, Khar-Nuur [2].

Fig. a. The distribution of lakes on the altitude in western Mongolia; b Dependence of salinity of lakes on the amount of water mass. 1 – freshwater lakes; 2 – soda lakes; 3 – chloride lakes; 4 – sulfate lakes.

Most of the lakes in this region belong to the type of soda lakes with salinity from 5.1 to 99.6 g / l, which are the first subtype. These include lakes, as Shaazgay-Nuur, Khar-Nuur (small), Ayrag-Nuur, Uvs-Nuur, etc., which are typically characterized by the volume of water masses greater than 0.1 km³. It is located and the lake. Hirgis-Nuur - the second depth (47m) and the third area (1407 km²), undrained reservoir Mongolia [3], the salinity reaches about 8 g / l.

However, there are exceptions - the lake. Davsan Nuur, Baga-Gashun-Nuur, Baga-Nuur and Suuzh-Nuur are chloride type. Some lakes salinity reaches 418 g / l, which may be due to their small volumes (all less than 0.0002 km3 of lake), respectively, increased evaporation from the lake surface and the presence of additional sources of supply chloride waters.

So, in the investigated region of the studied lakes is dominated by soda (48%), followed by chloride (41%) and relatively rare sulfate (11%), which in its arrangement is strictly subordinated to the location of their height above sea level, as well as morphological and climatic features.

References:

1. Rasskazov A.A., Abramov A.V. On the soda lakes of the Mongolia / / Lithology and Mineral Resources, № 6, 1987. P. 88-99.

2. Sevastyanov D.V., Shuvalov V.F., Neustrueva I.J. Limnology and paleolimnology in Mongolia. St. Petersburg.: Science, 1994. 304p.

3. Tserensodnom J. Catalogue of Mongolian lakes. Ulanbatar: Shuuvun Saraal, 2000. 141p. (In Mongolian.)

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