Eutrophication in reservoirs - Case study: reservoir of Rio Bonito (ES)

The Rio Bonito Hydropower Plant reservoir is located in the Santa Maria da Vitoria River watershed, state of Espirito Santo, Brazil, a major water supply source for the Great Vitoria metropolitan region. This river receives significant nutrient input from domestic sewage, agricultural crops, farms and piggeries. The study presents as main objective the analysis of the conditions of the cited water body, considering eutrophication aspects, for the hydrological year from October 2008 to September 2009, based on the results from bimonthly water quality monitoring developed within, upstream and downstream the reservoir. It was verified the influence of rainfall and seasonality on different water bodies trophic states classification methods. Trophic state classification was made according to Trophic State Index (TSI) and different mathematical models, including Salas and Martino, OECD, and Carlson and Lamparelli models. It was concluded that different classification models may result in different trophic level classes and that rainfall and seasonal conditions present large influence on the classification. Thus, it is very important the choice of models and indices according to the region weather and water bodies conditions. It was also concluded that water from the river monitored point located downstream the reservoir presented better quality than that from point located upstream, indicating that the reservoir may be working, improperly, as a stabilization pond.