Proveniência de sedimentos para os ecossistemas estuarinos do litoral Oeste do Ceará

Abstract

Estuaries are ecosystems that present their formation related to the relative flutuations of the quaternary sea level, being the sedimentary records that occur in these environments of relevance for studies related to current sea level and towards the mean sea level rise itself. The fine sediments of different origin can be distinguished by their associations of clay minerals, as they can serve as tracers for sediment pathways, even over long distances. Based on granulometric, mineralogical and geochemical analysis, the present study aims at evidencing sediment sources and filling the estuaries of the Acaraú and Coreaú rivers, in addition, correlating the clay minerals and geochemical carriers as a proxy for pollutants identification for the estuarine environment. In both estuaries, the clay mineralogical assembly is composed predominantly of kaolinite, illite and smectite. There are also minerals accessories such as: quartz, rutile, pyrite, lepdocrocite and calcite. Surface samples and sediment cores collected in the Acaraú estuary show that the estuary is predominantly filled by marine sediments. In the Coreaú estuary the influence of marine sediments is observed in very great distances of the mouth of the river. In both estuaries, the great contribution of marine sediments occurs due to the lack of entrance of fluvial sediments because the climatic characteristics in the region, besides the influence of the anthropic activities like the dams. Regarding the distribution of the main geochemical pollutants carriers in the Acaraú estuary, a distribution was correlated with the use and occupation of the soil in the estuary. With the results obtained, it is concluded that the climate is one of the most important controlling variables of the sediment sources for the estuaries in the west coast of the Ceará state.