ИСТИНА

Most of the lakes in European Russia are significantly affected by pollution. In Moscow Region, only a handful of lakes remain in their natural state, and their number is constantly further decreasing. In those circumstances, it is important to understand the consequences of increasing pressure on aquatic ecosystems, particularly nutrient loading. Lake Glubokoe, a small mesotrophic lake in Moscow Region, Russia, was targeted as a subject for this research. Lake has no inlets and isn't affected by human activity, allowing to suggest that the lake’s natural state is not altered. One-dimensional MyLake model was used to calculate annual dynamics of vertical distributions of water temperature, chlorophyll, and mineral phosphorus concentrations. Data from Mozhaysk weather station was used for meteorological input. The model was calibrated on extensive field data from 2017 and evaluated on less frequent monitoring data from 1991–2015. Model validation showed a good convergence of model output and observations after calibration. The possible consequences of increasing phosphate loading into the lake were studied by conducting several model scenarios calculations. Phosphate concentrations for different scenarios were set according to Russian standards. These regulations allow different phosphate concentrations in wastewater runoff depending on receiving lake’s trophic state. Wastewater discharge was also varied in different scenarios. Simulation results show the trophic state of Glubokoe Lake to be shifting to eutrophic even when phosphate concentration in wastewater is within the limits set for mesotrophic lakes. If phosphate concentration in wastewater is set according to regulations for eutrophic lakes, the effect of phosphate loading becomes devastating, leading to rapid degradation of the lake ecosystem. It is also shown that phosphate concentration plays a more critical role than wastewater discharge.