Abstract
The Carlson’s (1977) Trophic State Index (TSI) is a widely employed tool to estimate the degree of eutrophication in a reservoir. In Brazil, the need of a classification system that would take into account regional characteristics employed adjusted indexes generated by data from reservoirs in the southeastern region of the country. Current research compares responses for Carlson’s TSI (1977) and its derivations for Brazilian reservoirs from data collected in the Pereira de Miranda Reservoir (State of Ceara, Brazil), and analyzes the influence of local conditions on results and their applicability to reservoirs in the semiarid region. TSIs were calculated by data on total phosphorus, chlorophyll a and water transparency. The reservoir was estimated as mesotrophic based on the chlorophyll a variable, and between eutrophic and hyper-eutrophic when based on total phosphorus data and water transparency. Results showed the need to consider intrinsic factors in the discussion on the applicability of TSIs to reservoirs in the semiarid region since the peculiar hydro-climatic conditions and morphometric characteristics make them even more vulnerable to disturbance agents, such as winds which have a significant influence on processes that determine the trophic state.
Highlights
Climate conditions, hydrological regime and pollution loads from rural and urban anthropogenic activities are some of the factors which act in a peculiar way over the dynamics of limnological processes in semiarid region reservoirs
In some Brazilian semiarid regions, annual variation in trophic status indicators is associated with seasonal fluctuations in hydrological regime, led by rains during the first half of the year (BOUVY et al, 2003; CHAVES et al, 2013; CHELLAPPA; COSTA, 2003)
This variation is associated with stronger winds; in addition, it is increased by the lower average depth in reservoirs at this time of year (BRAGA et al, 2015; ESKINAZI-SANT'ANNA et al, 2007; FREIRE et al, 2009; DANTAS et al, 2012)
Summary
Hydrological regime and pollution loads from rural and urban anthropogenic activities are some of the factors which act in a peculiar way over the dynamics of limnological processes in semiarid region reservoirs. They have a significant influence on changes in the systems' trophic conditions, characterized by increase in nutrient concentrations and phytoplankton biomass. Carlson (1977) adopted the algal biomass as basic reference to define the trophic state and formulate a numeric rating system from variables related to aquatic environment trophic conditions. Since the index was originally based on data obtained in glacial-origin lakes of temperate zones, its unrestricted use in other climatic regions has been criticized
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