Estudo sobre as variáveis responsáveis pela eutrofização das águas dos reservatórios do semiárido cearense

Abstract

The characterization of the substances present in the waters of the reservoirs (reservoirs) used for both human consumption and for the most varied purposes constitutes an important tool to evaluate the environmental quality of the same. In these aquatic environments, the quantity and quality of the biomass, together with the total phosphorus, vary greatly according to their origin and contribute to the calculation of the Index of the Trophic State (ITS). Studies carried out since 2008 by the Laboratory of Environmental Chemistry, through a contract with COGERH show that the concentration of chlorophyll is not related to the cyanobacteria count, as would be expected, so it is necessary to search for another variable (s) that justify the high content of cyanobacteria present in our reservoirs, of which 75% are with ITS located between eutrophic and hypereutrophic. Research shows that the high growth of cyanobacteria (blue algae) in water bodies is favored by the excess amount of nitrogenous and phosphorous nutrients, and that the amount of phycocyanin pigment is much higher (over 75%) than other pigments. Currently, few studies are available on the concentration of phycocyanin in Ceará reservoirs. It is intended to analyze this pigment by using the molecular fluorescence technique, the concentration of chlorophyll and nutrients by spectrophotometry and characterize dissolved organic matter, both in the dry and rainy period, to verify if there are correlations. In this work, the annual trophic level of reservoirs studied was evaluated, all classified as eutrophic. For phycocyanin, more information about its optical characteristics was obtained in the Ceará reservoirs and observed the low amount of pigment (values below the limit of quantification). In the results, the organic carbon available in the reservoirs was predominantly of allochthonous origin, with divergence observed in the Pacajus reservoir. Statistically, a linear relationship between chlorophyll and cyanobacteria counts was observed, in addition to a significant contribution of the variable transparency related to other variables. The information generated here can contribute to the direction of actions that favor the environmental quality of the reservoirs.