Development of trophic indices for lake Onego using of the ecological information system

GIS technologies were used to study the spatial distribution of zones with different trophic conditions in the water area of Lake Onego. Empirical data on the trophic conditions of waters sampled in 1982–2020 were as the basis for the map development. Two periods, before and after 2000, were considered separately to assess the impact of climate change. As indicators of trophic conditions, the number of saprophytic bacterioplankton, biomass of crustacean zooplankton, concentration of chlorophyll “a” and water transparency were used. All characteristics were converted to a normal distribution, and the values at individual points were interpolated for the entire water area of the lake, which was presented as a network of 544 squares. Each cell of the water area was characterized by four values of indicators. To assess trophic conditions, multivariate statistics (principal component analysis) and an expert system (Bayesian classifier) were used. The first principal component can be considered as the integral value of trophic conditions in a given part of the water area. The Bayesian classification method allows to get an estimate of the probability of classifying each cell in the water area as “high trophic conditions” and “low trophic conditions” and assign a significance threshold (p = 0.05). The cartograms built on the basis of both methods are basically the same. Most of Lake Onego area is characterized as low trophic conditions. The vast area with high trophic conditions was identified in the northwestern part of Lake Onego where on the coast large cities are located (Petrozavodsk and Kondopoga), which is associated with active anthropogenic pollution in the last century. In recent years, due to industry recession, trophic conditions in this area has sharply decreased, with the exception of Kondopozhskaya Bay, where there is an increase in water pollution as a result of trout farms.