Caracterização limnológica do estuário do Rio Jaguaribe - CE e do estuário do Rio Parnaíba - PI, Brasil

Abstract

The reactive phosphorus in water does not present conservative behavior and alterations in the biogeochemical conditions of water can foment the bioavailability of this element. On the semiarid, these conditions are influenced primarily by the climatology of the region which will determine the frequency of occurrence, intensity and quality of freshwater flow toward to the estuary. Both estuaries analyzed are located in oriental northeast coast, characterized mainly by short periods of rain and long periods of drought, however the estuarine behavior has shown differences between them due to different watersheds uses and inner properties. Phosphorus discharge increases, by naturally or anthropic sources, can start seaweed blooms which can act on the reduction of waters quality. Therefore, phosphorus and chlorophyll a analysis on the water are able to identify trophic state determining water quality, dilution and capacity of restoration of the estuarine environment. The calculations and classifications of Trophic State Status were based on the adapted methodology by Lamparelli (2004). The total phosphorus at the Main Channel of Jaguaribe River Estuary varied between 6,6 to 164,8 μg/L, at Channel of Cumbe, 162,4 to 187,4 μg/L, and, at Channel of Love, 27,6 to 41,5 μg/L. Chlorophyll a variations were 0 to 9,5 μg/L at the Main Channel of Jaguaribe River Estuary, while at the secondary channels were 42,39 to 62,67 μg/L (Cumbe’s Channel), and 3,31 to 3,76 μg/L (Love’s Channel). The main channel of Jaguaribe river’s estuary presented different degrees of trophy, fluctuating from ultra-oligotrophic to eutrophic, while Cumbe’s Channel presented as Hypereutrophic, and Love’s Channel as mesotrophic. For Parnaiba river’s estuary, total phosphorus variation at the Main Channel was from 36,2 to 72,9 ug/L, for Igarapé dos Periquitos’ Channel from 30,4 to 49,5 ug/L, and at Tatus’ Channel, from 27,2 to 32,5 ug/L. Chlorophyll a varied from 3,53 to 23 μg/L, for Igarapé dos Periquitos from 4,31 to 12,87 μg/L, and Tatus channel from 7,66 to 8,57 μg/L. The Parnaiba river’s estuary, as a whole, presented an eutrophic environment, with a super eutrophic region and another one as mesotrophic. Therefore, the eutrophication of water bodies can be controlled both by natural and anthropogenic sources, where local variations of the biogeochemical conditions can act in the purification capacity and in the contamination of these waters, influencing their trophic state indexes.