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Ground sediments of water objects as an indicator of the load of people’s technological activities

Congress: 2008
Author(s):

Keyword(s): Ground sediments, Hydro-ecological systems, People’s technological activities, Heavy metals
AbstractIntroduction Ground sediments (GSs) are integral parts of hydro-ecological systems. They are one of the most informative objects to be studied when estimating a hydro-ecological system. Physical and chemical composition of GSs gives us information about a longer period than water analysis may do as the last may describe the quality of water only in the moment of sampling. GSs not only define the quality of water but also exert influence upon the composition of water objects and processes taking places in them. Bulk of polluting substances in eco-systems passes from water into GSs that results in the fact that bottoms often contain higher concentrations of polluting substances while their concentration in water might be not so nigh. As economical development of water-catchment areas and reservoirs goes further, anthropogenic factor becomes of a greater importance in formation of GSs. Especially dramatic this dependence shows itself in river basins of urban regions. From the point of view of water quality, heavy metals (HVs) and their compounds have constantly been being the most dangerous - characterized by their high toxicity. Heavy metals exert influence upon the quality of natural water, they are conservative polluting substances and do not decompose in natural water but only change their “life styles”. Objective We have tried to estimate the load of people’s technological activities upon the water system using the results of the analyses of GSs pollution in Chirchik- Akhangaran basin of the Republic of Uzbekistan. The objects of the research. The objects of the research were water streams of Chirchik-Akhanfaran basin. The concentration of polluting components in the ground sediments of water objects within Tashkent City and Tashkent region (the most polluted territory in the Republic of Uzbekistan) was studied during the first year of the research in 39 points, 18 of them being situated on rivers, 12 – on large main canals, 2 – on collectors and 7 – on lakes. Nine points were defined as background ones as they are situated higher than the zone of intensive anthropogenic activities. During the next years there were selected and reserved for studies 16 the most representative sampling points. In all the points there were made samplings of water and GSs. In the samplings there were defined HMs (Cd, Ni, Cu, Zn, Pb, Hg) and a number of other polluting substances. Those samplings of water and GSs were made once a month during three years. To make an account of the contribution of tributaries into the pollution with heavy metals, the supervision net included dams located higher and lower than confluences and also in the mouths of main tributaries. Methods Active forms of metals were defined through the method of atom-absorbtion spectroscopy with inductionally combined plasma. Estimation of the GSs pollution level with heavy metals: There is a number of methods of estimation of GSs pollution level. The most widespread is to compare the mass concentrations of heavy metals with Clark’s constants, background concentrations, official permissible levels or other earlier possessed data. Another method of estimation of GSs pollution level is to find coefficients of the concentration of elements K equal to the ratio between the quantity of an element on the polluted area and its background value, as well as total indices of pollution Z=∑K-(n-1), n – the number of elements. Estimation of GSs pollution level for separate elements may also be conducted through the method of iheo-classes or indices of geo-accumulation (Mueller, 1979). Using the same initial materials these indices may be calculated as following: I-geo, n=Log 2 (Cn/1,5Bn), Cn – measured concentration of the element n in GSs (fractions - not less than 0.020 mm); Bn – geo-chemical background concentration of the element n. Using this equation GSs may be defined as following classes: Iheo-classes 0 and 1 are chacterised with the pollution of elements under 1.5 and 3 background values, class 2 – 6-multiplied excesses, class 3 – 12-multiplied excesses, class 4 – 24-multiplied ones, class 5 – 48-multiplied ones, class 6 – more than 48-multiplied local background. Results On the basis of the given classification we have compiled maps of GSs pollution for each studied heavy metal. Research experience in various countries showed that series of such maps allow estimate the loads of people’s technological activities upon ecological systems of water objects more precisely and reveal the most defective territories from the ecological point of view. Conclusion We have revealed the most ecologically defective territories of Chirchik-Akhangaran basin of the Republic of Uzbekistan, conducted correlation of technological load estimated through ground sediments and biological states of all studied point of the water systems of the Republic of Uzbekistan.
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