Avaliação do efeito da seca prolongada nos reservatórios Acarape do Meio e Gavião

Abstract

In recent years, the state of Ceará has been living with an extensive period of drought, with quantitative (water scarcity) and qualitative problems, such as eutrophication of reservoir water. Eutrophication is the process by which the aquatic environments undergo an enrichment in nutrients, mainly of phosphorus and nitrogen. The objective of this work is to evaluate and characterize the changes occurring in the Gavião and Acarape do Meio reservoirs, located in the municipalities of Pacatuba-CE and Redenção-CE, respectively, during the dry season. In the study, the variation of the Trophic State Index (IET) and the influence of the extensive temporal dryness in the IET during the years 2012 to 2017 are analyzed. The IET classifies the bodies of water into different degrees of trophy, being determined by the concentrations of total phosphorus and chlorophyll a from samples collected from water. The concentrations of nutrients from the studied reservoirs, collected at 0,3 m depth at GAV-05 (Gavião) and ACA09 (Acarape do Meio), were analyzed monthly in the LAQUIM-UFC, using spectrophotometric methodologies proposed by Eaton et al. (2005). It was verified that the trophic degree of both dams is high, being classified basically into two categories: supereutrophic and hypereutrophic. These categories alert to waters affected significantly by high concentrations of organic matter and nutrients, associated with episodes of algae blooms or fish mortality, deteriorating water quality and impairing their multiple uses. Statistically significant differences were noted in the temporal evaluation of the mean IET (IETM) for the two dams and a strong statistically significant negative correlation of the IETM and the IET of chlorophyll a with the stored volume of the hawk weir. Although there are some moderate and strong positive and negative correlations of some IET’s with the annual precipitation of the municipalities, with the volume of Acarape do Meio and between the IET (PT) × IET (Cl_a) of the two dams, it is verified that not yet there is a statistically significant correlation between these multiple comparisons. The mean IET’s did not change under the effects of the rainy and dry season. However, it was verified that the prolonged drought period in Pacatuba and Redenção, associated to punctual and diffuse sources of pollution located around the dams, negatively affected the water quality of Gavião and Acarape do Meio.