Study of Changes of Trophic Status of the Kuchurganske Reservoir in 2006-2018

Abstract

Purpose. Assessment of the trophic status of water in the Kuchurganske Reservoir in 2006-2018. Methods. Determination of hydrological, hydrochemical and hydrobiological characteristics of the water body's environment has been done using standard methodologies. Four indicators of water eutrophication have been used: chlorophyll a concentration, bacterioplankton number, trophic indices TSI and TRIX. Results. Features of physicochemical characteristics of water in the water-body have been analysed. Higher water temperature has been registered in the middle and lower parts of the water-body compared with its upper reaches. Mineral content increase in water has been found in the direction from lower to upper part; the critical for hydrobionts life decrease of oxygen concentration has been registered in the upper reaches the most often. Analysis of long-term changes in chlorophyll a and bacterioplankton has been carried out. Statistical interconnections have been established between trophic state indicators and physicochemical characteristics of the reservoir. A close positive correlation has been registered between chlorophyll а content and bacterioplankton number, which is caused by the functional dependence of bacteria on the organic matter produced by phytoplankton. It has been shown that with an increase of water volume in the reservoir the value of these indicators of trophic status went down, which was proved by close negative correlation dependence between those values and the depth of water-body. It was demonstrated for the first time that water transparency revealed close significant negative correlation with all the indices and indicators of water trophic status, which evidenced the possibility to use the transparency as a simple indicator of water trophic state as established that the Kuchurganske Reservoir’s trophic status assessment on chlorophyll a, bacterioplankton and the TSI trophic index practically coincided and evidenced the increase in trophic status of the water-body from eutrophic to hypertrophic in last 2016-2018. The reservoir’s upper reaches were characterized by higher water trophicity compared with the central and lower parts. The values of TRIX trophic index developed for marine water assessment had practically always been showing higher trophic status compared to other indicators.