Water quality modeling of a eutrophic drinking water source: Impact of future climate on Cyanobacterial blooms

Cyanobacterial blooms are becoming more frequent in freshwater sources, causing concern throughout the world. Cyanobacterial blooms affect human health and the entire environment. Numerical modeling is an effective tool for investigating aquatic systems. In this study, a 3D hydrodynamic and water quality (ecological) model was used to simulate eutrophication of a drinking water source, Lake Vomb, in Sweden under present and future scenarios. The hydrodynamic model was set-up in MIKE 3 FM software based on meteorological, hydrological, and water quality data. The hydrodynamic model performance was satisfactory in terms of the water temperature simulation, with root-mean-square-error (RMSE) ranging from 0.38 to 1.2 °C. In the ecological model, Chlorophyll-a (Chl-a) was used as a proxy for Cyanobacteria, and the model proved acceptable in simulating the Chl-a concentrations, with a Nash-Sutcliffe efficiency (NSE) of 0.93 and 0.87 for calibration and validation respectively. The findings revealed that external nitrogen loading and internal phosphorus loading had significant impact on the nutrient concentrations in Lake Vomb. The findings also showed a correlation between Chl-a levels and total phosphorus levels in the lake. To simulate future water quality in the lake, two Representative Concentration Pathways (RCP) for the year 2050 were used to make projections for changes in air temperature and precipitation. Under the projected future climate, the simulations showed a considerable rise in Cyanobacteria biomass independent of the changes in external nutrient loading. The model findings can assist water managers in planning mitigation strategies by identifying major nutrient sources.