Numerical modeling of the influence of reservoir management on the algal blooms of San Roque

Abstract

The San Roque reservoir, first multipurpose reservoir in Latin America and, at the time, the largest in the world, experiences blooms of potentially toxic cyanobacteria and dinoflagellates. Nutrients reach this body of water through its tributaries and from the surrounding city, Villa Carlos Paz, whose urban liquids are partially treated and released into the reservoir. This work presents the first tridimensional numerical simulation of an algal bloom in the San Roque reservoir calibrated by field measurements. The influence of the water level and the impact of the amount of nutrients and their distribution on phytoplankton biomass are evaluated. On the one hand, algal biomass was found to decrease by 8% and increase by 12% for water levels one meter above and one meter below the measured water level, respectively, during bloom. On the other hand, complete wastewater treatment produced a reduction of up to 65% in this period, while other techniques (no treatment, transfer of liquids produced by the current plant, and a 10% decrease in phosphorus produced in the surrounding city) do not represent significant improvements. Finally, a spatial and temporal analysis of the field measurements shows that the center of the reservoir is the most representative point of the total phytoplankton biomass of the entire reservoir, with Pearson and Spearman coefficients of 0.63 and 0.90, respectively. In addition, this point has little temporal variation during the morning, when field measurements are made, reaching variations of less than 50%.