Estudo do "standing-crop" da água do estuário do rio Cocó(Ceará-Brasil), como indicador das modificações físico-químicas do meio

Abstract

Many aquatic ecosystems are having their natural characteristics degraded, mainly by human action. Among these ecosystems the estuaries, that have a vital significance in the coastal water fertilization, are being progressively modified by environmental impacts of manifolds and indiscriminate uses. The goal of this work was Cocó river estuary water characterization, using information about a-chlorophyll concentration in the phytoplankton in the investigated area. In order to carry out this research, monthly sampling was carried out in four stations for a period of twelve months (July, 2001 to June, 2002). The samples were collected at the surface, during higher and lower tides, in the same day. For each station in situ measurements were carried out for air temperature, water transparency, pH, water temperature and salinity. Dissolved oxygen, inorganic nutrients, qualitative phytoplankton studies and a-chlorophyll concentration were performed in laboratories. The acquired data were analyzed for each sampling station and tide condition. The data were statistically analyzed using Pearson’s multiple correlation and multiple regression between a-chlorophyll concentration and physical-chemical parameters. The Cocó river plankton community is characterized by high quantity and low diversity. The predominant group was diatomaceaes being the dinoflagellates the less representative group, with a single gender even so in small quantities. The predominance of Melosira gender characterized the study area as a polluted, mainly by domestic sewages. The rotifers and copepods were the principal in the zooplankton community being recorded, in minor frequency, ciliates, cladoceras, ostracodas and decapodous larva. The Cocó river estuary phytoplankton biomass (a-chlorophyll) in the study area shown a rising gradient from downstream stations (E1 and E2) to upstream ones (E3 and E4), with minimum values of 0,52 mg.cl”a” m-3 in the higher tide in E2 station (June, 2002) and maximum values of 113,66 mg.cl”a”.m-3 in the lower tide in E4 station (October, 2001). The correlation study showed the accelerated degradation process in the Cocó river due to domestic and industrial sewages. The regression analysis between a–chlorophyll and physicalchemical parameters presented direct and inverse relationships, for each station and in different tide condition, evidencing time-space variation of the environmental conditions of Cocó river estuary.