Total volatile solids may aid in trophic state assessment in subtropical reservoirs

Brazilian artificial reservoirs are multi-purpose systems of great importance for the community since they are used for drinking water supply, energy generation and agricultural irrigation. Anthropogenic eutrophication is an environmental problem of special concern because it can restrict water use due to aquatic systems deterioration. Therefore, trophic state prediction is an important tool for the rapid detection of water quality decrease and the identification of priority areas where action is needed. Within this context, the aim of this research was to assess the role of TVS (total volatile solids) in predicting the trophic status of subtropical reservoirs. To achieve this goal, four stations in the Itupararanga Reservoir (São Paulo State, Brazil) were sampled during dry, intermediate and rainy periods to determine total suspended solids concentrations in different depths of the water column, in addition to other variables (e.g. phosphorus, nitrogen, chlorophyll-a). Through a linear regression between TSI (trophic state index) and the TVS concentrations, an equation relating these two variables was generated (R² = 0.67). New TSI values (named TSI_calc) were calculated and analyzed against the observed ones (TSI_obs, determined through the total phosphorus and chlorophyll-a concentrations). The results suggested that TVS may be considered an interesting variable to predict the trophic state of subtropical reservoirs.