Avaliação do índice de estado trófico do sistema de reservatórios em cascata que abastece a bacia metropolitana de Fortaleza, CE

Abstract

The contamination of aquatic ecosystems resulting from human activities has raised a number of ecological concerns in recent years. The inadequate use and occupation of land associated with population growth, as well as the rapid industrial expansion observed in recent years, are considered to be the main responsible for the change in the quality of water in rivers, reservoirs and lakes, allowing the occurrence of an increasingly phenomenon more frequent, eutrophication, which mainly affects springs located in semiarid regions. This phenomenon occurs due to the increase of nutrients, such as phosphorus and nitrogen, arising from human action, representing a serious risk to the health of living beings and drastically reducing water quality. In view of this problem so common in the Northeast, which suffers from water scarcity, eutrophication also represents a serious threat to water sources, especially when it comes to water transfer systems between reservoirs, such as the Cascade System in the Metropolitan Region of Fortaleza (SCRMF), comprising 6 reservoirs (Castanhão, Curral Velho, Pacajus, Pacoti, Riachão and Gavião). Thus, it is evident that cascade systems generate a series of effects on water quality conditions, in particular, due to variation in residence time and nutrient resuspension. In view of this problem, it is essential to carry out a qualitative analysis of water, as it is essential for human and animal consumption. In this sense, the Trophic State Index (TEI) appears as an important instrument to assess how eutrophic a reservoir is. Therefore, the present work deals with a bibliographic compilation in order to determine the EIT of the cascading reservoirs that supply the metropolitan region of Fortaleza, Ceará, based on the methods of Carlson (1977), Toledo et al. (1984), Lamparelli (2004), Cunha (2012) and Rolim (2016), aiming not only to calculate the EIT, but also to classify the water body according to its trophic state. For this analysis, data on total phosphorus, chlorophyll-a and transparency were initially collected from COGERH, for the period 2017 to 2021. After estimating the IET, it was concluded that most methods classified the trophic level of the water sources of the SCRMG between eutrophic, hypereutrophic and supereutrophic, also observing some occurrences of an oligotrophic and mesotrophic state, especially in the methods of Toledo et al. (1984) and Rolim (2016).