ASSESSING THE STATE OF THE LOWER DON ECOSYSTEM USING REMOTE SENSING DATA
The methods of aquatic environment remote near real-time monitoring based on water leaving reflectance spectra shape analysis were tested on water bodies of type II (muddy productive) in Lower Don. Remote spectrometric surveys of river Don, river Seversky Donets and Tsimlyansk reservoir along with water sampling for laboratory analysis were carried out on board. We present visible reflectance spectra (420-750 nm) acquired in end of august, 2020. According to shapes of reflectance spectra, phytoplankton was distributed quite uniformly in eastern part of the reservoir, while its chlorophyll a concentration was rather high and varied according to analytical data - from 11.0 to 315.9 mg/m3 and according to spectrometric data - from 25.6 to 109.0 mg∙m-3 and cyanoprokaryote mass blooms state in different parts of the reservoir. In the Don River, the phytoplankkton chlorophyll a concentration varied over a wide range from 25 to 35 mg/m3. The trophic status of the ecosystem in various parts of the Lower Don varied from mesotrophic to hypereutrophic, with blue-green microalgae blooming at most stations. This trophic state assessment was validated by phytoplankton chlorophyll a and phycocyanin concentrations estimated applying published biooptic algorithms to reflectance spectra and chlorophyll a concentration estimated by common spectrophotometric technique in water samples. Comparison of estimates confirmed that spectrometric surveying allows for near real-time assessment of water body state, its trophic state and serves as a basis for detailed chemical-biological monitoring of water bodies.