Eutrophication, Oligotrophication, and Benthiphication in Naroch Lakes: 40 Years of Monitoring
Naroch lakes present a system of three interconnected water bodies of different trophic state, many years monitoring of which allowed to establish and reveal a number of fundamental patterns of functioning of aquatic ecosystems. Over the past 60 years, several stages in the evolution of the structure and functional organization of the ecosystem are clearly traced. Within the framework of the work the following periods were considered: 1) anthropogenic eutrophication (1978-1983); 2) oligotrophication (from 1984 to 1990 for Lake Naroch and from 1984 to 1990 for Lakes Myastro and Batorino) and 3) the period of bentification (since 1991 for Lake Naroch and since 1990 for Lakes Myastro and Batorino to the present). The values of the most part of parameters that are taken into account when assessing the trophic state of ecosystems (phosphorus, chlorophyll, phytoplankton, seston) are significantly reduced at bentification period compared to that of anthropogenic eutrophication. In the same time gross primary production of plankton in Lake Naroch actually did not change. One of the important reasons for this may be an increase in the depth of trophogenic layer and as a result an increase in its volume in regard to the entire volume of the lake. Production of submerged and emergent macrophytes in Lake Naroch during the period of bentification increased in 2 and 4 times respectively, compared with the period of eutrophication. The level of production of periphyton communities has not changed significantly. Based on the dynamics of the main hydroecological parameters of the Naroch lakes in different periods of their evolution, the uncertainty in assessing such a key characteristic of the ecosystem as its trophic state is evident, which can differ significantly depending on indicators that are used as the basis for its assessment in a specific waterbody.