Ecological state and monitoring of limnological and biological parameters in Lake Ladoga, Russia

Abstract

Lake Ladoga (17 891 km2) is the largest lake in Europe, with a 258 000 km2drainage area that extends to much of north-western European Russia and eastern Finland. Its ecosystem has been systematically investigated since 1976, and sporadically since the 1950s. Monitoring programmes have included studies on its hydrology, water chemistry and biology (phytoplankton, bacterioplankton, zooplankton, benthos, macrophytes and fish). The sampling frequency per vegetation season (spring, summer and autumn) has varied from 2 to 6 times, and samples have been collected at 20–60 fixed stations in the different zones of the lake. These long-term investigations covering over 40 years serve as a good basis for understanding the processes taking place in Lake Ladoga, as well as for assessing the changes and current environmental conditions. Until the early 1960s, Lake Ladoga was oligotrophic and characterized by good water quality; but within the past 30 years, as a result of human impact, its ecological state seems to have deteriorated. Especially since the 1970s, its trophic state has changed to mesotrophic, with elevated nutrient concentrations, reduced transparency and poorer fish catches, together with structural changes in its plankton, zoobenthos and fish communities. During the last decades, several planktonic, benthic and fish species that are sensitive to eutrophication have disappeared. Conditions in the whole lake, and especially at some of the worst-polluted sites, have actually improved in recent years, however, due to the closing of some of the sources of industrial pollution, and some signs of a recovery have been observed. The present species composition points to mesotrophic and eutrophic conditions in the coastal regions, but mainly oligo-mesotrophic conditions in the pelagic areas. The aim of this paper is to describe and assess monitoring practices in Lake Ladoga and the results obtained, future prospects, changes that have occurred and the current state of the ecosystems.