Avaliação de impactos ambientais em um estuário neotropical do litoral de Pernambuco, Nordeste do Brasil

Abstract

The Itapessoca Estuarine Complex, belonging to the Itamaracá Estuarine Ecosystem, is characterized by a history of intense economic activities that develop along the banks of its tributary rivers, often performed without any control or planning. In order to relate natural and anthropic events with the age of the sediment, a geochronology was carried out by the determination of Pb-210 in excess (fallout), by the Gas Proportional Flow technique. Firstly, geochronology was applied to trace mercury contamination in the estuarine ecosystem. Two sediment cores were sampled, stratified and analysed by the Gas Proportional Flow Counter technique for determination of Pb-210 activity, a radionuclide applied to geochronology. Mercury was quantified in sediment samples by Cold Vapor Atomic Absorption Spectrometry, ranging from 0.17 to 1.29 mg.kg-1 in deep sediments. From the Pb-210 results, sedimentation rates of 0.84 (±0.07) cm.year-1 and 1.03 (±0.22) cm.year-1 confirmed Hg contamination in Itamaracá since 1965. Extreme precipitation and drought events have also been related to the distribution pattern of Hg concentrations in deep sediments. To investigate possible disturbances in the recent sedimentation processes in the study area, 20 surface sediment samples and 2 cores were collected for analysis of chemical elements Al, Ca, Fe, K, Mg, Mn, Ni, Pb, Si, Sr, Ti and Zn concentrations, determined by Energy Dispersive X-Ray Fluorescence - EDXRF technique. Through the enrichment factors and ratios between some elements associated with geochronological data, it was possible to identify geochemical changes in the sedimentation of the sampled points, with an increase in minerals associated with fine fractions and a decrease in the proportions of elements associated with coarse fractions. The geochronology revealed that the enrichment of Pb and the marked increase in the enrichment factors of Ca and Sr are strongly associated with the anthropic activity of the region (mining and cement factory). A total of 76 species distributed in 33 families were collected. Aspects such as functional guilds and diversity were investigated and compared between Catuama and Itapessoca. Although many species of commercial importance in the region are young, only one species was classified as vulnerable (IUCN). Statistical analyses showed that electrical conductivity of the water, Total Dissolved Solids, salinity and the metal zinc were the factors most correlated with the fish assemblage variation although no clear pattern were found. This study revealed that the study area has relevance for feeding and shelter for several marine species and that natural processes seem to exert more influence on the composition of the occurring ichthyofauna.