Variance analysis and comparison of trophic state indexes: Rio Bonito and Suíça power plants reservoirs

<p></p><p>ABSTRACT Reservoirs have been built worldwide to regularize flows for improvement of watersheds water resources use conditions for different purposes, such as human and industrial supply, irrigation and power generation. Waters of rivers and streams that carry excessive nutrients from sewage and fertilizers, when dammed, may be subject to significant qualitative changes resulting from eutrophication processes. Several indexes have been created by researchers for trophic state classification of water bodies. In this study three trophic state indexes (TSIs), developed by Carlson (1977), Lamparelli (2004) and Cunha, Calijuri and Lamparelli (2013), were analyzed and compared, through the application to two power plant reservoirs, denominated Rio Bonito and Suíça, located in the Santa Maria da Vitoria river watershed, Espírito Santo state, Brazil. Results from 20 water quality monitoring campaigns were considered, conducted between October 2008 and July 2014. The reservoirs receive nutrient loads originated from domestic sewage, agricultural crops and chicken farms. It was concluded that application of different models may result in very different trophic state class definition. The application of the Carlson model (1977), developed for temperate climate reservoirs, resulted into higher eutrophic class level, classifying the reservoirs mainly as eutrophic and mesotrophic. Lamparelli (2004) and Cunha, Calijuri and Lamparelli (2013) models, developed for tropical/subtropical climate reservoirs, presented closer results, classifying the reservoirs mostly as oligotrophic. It was also concluded that seasonality and rainfall in reservoirs catchment areas may influence very significantly the reservoirs water quality parameters and trophic state classification. The wide variety of trophic classes chosen for the reservoirs, in this work, indicates the importance of the proper choice of models and indexes, according to the prevailing conditions in the water bodies of interest.</p><p>