Ecohydrological evolution in the catchment of Lake Druksiai, Lithuania, under anthropogenic pressure

The catchment area of Lake Druksiai (the Ignalina Nuclear Power Plant cooling basin) is exposed to severe anthropogenic pressures due to urbanization, industrialization and, to a smaller scale, to agricultural development. Ecological changes in the lake are investigated in connection with the water balance of Lake Druksiai and the interaction of surface water and groundwater in the catchment. The main sources which contribute to the most active water exchange in the lake are total surface runoff, precipitation and artificial circulation of water used in the cooling system of the reactor turbine condensers of the Ignalina NPP. According to the observation and model results, natural groundwater flow does not influence significantly the water exchange in the lake. However, groundwater, particularly of the confined Upper-Middle Devonian aquifer, is the basic source of centralized water supply in the region and indirectly has become the most significant chain of nutrient transport to the lake. Due to this impact, the trophic state of the lake has changed from (oligo)mesotrophic to almost eutrophic within twenty years of operation of the Ignalina NPP. The increase of the water surface temperature and alteration of vertical thermal stratification have stimulated the main ecological changes in Lake Druksiai. (author)