BIOCUMULATION OF MICROELEMENTS IN BENTHIC ORGANISMS AND THEIR MIGRATION IN THE BIOTA OF THE LAKE BALKHASH
The paper studies the peculiarities in the distribution of microelements in benthic organisms of the Lake Balkhash. It is found that the pollution of the lake ecosystem with toxicants causes a significant depletion of the species diversity of benthos and reduces its quantity. Zoobenthos biomass in the Western Balkhash ranged 17.46-35.95 g/m <sup>2</sup>, in East Lake Balkhash - within 1.40-3.21 g/m <sup>2</sup>. Gross production of benthos in the western part of the reservoir was 87.52-162.95 thousand tonnes, in the eastern part - 20.61-138.07 thousand tonnes. Particular attention is paid to the study of the mechanism and the nature of mineral metabolism between forage organisms and the environment, including biological cycles of migration of microelements in the "ground - benthos" system. The range of tolerance of heavy metals in the sediments, within which benthos of the Lake Balkhash may exist, is 0.05-1.50 g/kg. The metal content in the soil in the amount of about 2.12 g/kg leads to almost complete disappearance of the bottom animals. Biomass of unpolluted waters of the Western and Eastern Balkhash is 9.49-18.88 g/m <sup>2</sup>, which is much higher than in the waters in the zone of technogenic impact. Gross output contains in its structure 4887.9 tonnes of total number of microelements, 1.208.5 tonnes of them are recycled by fishes with benthos in the West Balkhash and 756.7 tonnes - in the Eastern Balkhash, the total consumption is 1965.2 tonnes. The remaining part of microelements, 2.992.7 tonnes, in the form of organic compounds is decomposed with the withering away of forage organisms. The studied chemical elements on their content in zoobenthos form the following descending order: Zn > Cu > Pb > Ni > Cd = As > Hg.