Spatial-temporal Variability of the Chlorophyll “a” Concentration in the Krasnodar Reservoir According to the Satellite Images’ Data

Abstract

The Krasnodar Reservoir has undergone significant transformations during its operation since 1973. As a result, of active delta formation of the Kuban and Belaya rivers, the reservoir was divided into two autonomous reservoirs, its area decreased by 35 %. The study is aimed at determining the significance of the eutrophication factor in the transformation of the Krasnodar Reservoir. Methods. Based on 51 Sentinel-2 satellite images for 2015–2020 the results of calculations of the concentration of chlorophyll «a» as an indicator of phytoplankton biomass in the reservoir are presented. The MSI sensor calculates the concentration of chlorophyll a (chl «a») based on the normalized chlorophyll difference index. Chl «a» estimates were obtained for a total area of 277 km2; the main bowl of the Krasnodar Reservoir and the Tshchik Reservoir, which was cut off from it. We have built maps reflecting the spatial and intra-annual variability of chl «a». Results The highest average concentrations of chl «a» are characteristic of the shallow upper part of the Krasnodar Reservoir, which is influenced by the runoff of the Kuban and Pshish rivers with an increased nutrient content. Locally high average values of chl «a» were recorded in the areas of the runoff current and in the estuaries of the left-bank tributaries. In the Tshchik water body with a low intensity of water exchange, the relationship between the concentration of chl «a» and hydrodynamic processes is not evident. We have revealed features of the annual cycle of phytoplankton biomass. It has been established that the trophic status of the reservoir is subject to seasonal variability: in spring, 2/3 of the water area correspond to eutrophic waters, 1/3 to mesotrophic waters; in autumn, the entire reservoir has a eutrophic status.