CHANNEL DREDGING EFFECT ON MORPHOMETRIC FEATURES, INDICATORS OF WATER AND BOTTOM SEDIMENTS QUALITY OF THE LAKE MANZHEROKSKOYE (ALTAI REPUBLIC)

The paper presents the results of a comprehensive assessment of the current ecological state of the important recreational object, i.e. Lake Manzherokskoye (Maiminsky region of the Altai Republic, the Russian Federation). The investigation was conducted in August 2018, just 2 weeks after the dredging works implemented in the framework of the environmental rehabilitation project. The studied morphometric, hydro/physical and hydro/chemical parameters of the reservoir are evidence of an increase in lake depth (with its maximum more than 2 m, up to 5.66 m) and water volume (more than 2 times, up to 1,16 million m3 ) that in the future will lead to the improved oxygen regime and the decreased inflow of biogenic matter. Bottom sediments are still represented by soils with a high content of organic carbon (up to 56,2±2.9 mg/dm3) and organic matter (up to 112.3±10,2 mg/dm3); detritus and organic silt (sapropel) dominate in the sediments. In all studied sites and depths of Lake Manzherokskoye, the water was polluted by roiled organic silts. The concentration of suspended solids reached 4.6 g/dm3, whereas transparency (by Secchi disk) dropped up to 0,5 cm. Vertical distribution of suspended substances points to the process of their deposition. Water quality of the lake is estimated as unsatisfactory because of the performed dredging works. Major pollutants of the lake water are phosphates (up to 0,417±0,042 mg/dm3), petroleum products (up to 0,4±0,1 mg/dm3) and organic substances (up to 342,2±35,8 mg O/dm3 by unfiltered water COD); their concentrations exceed MAC significantly. Water quality does not meet the requirements imposed upon the water bodies used for recreational purposes.