Caracterização geoquímica e mineralógica dos sedimentos do manguezal do estuário do Rio Coreaú, Ceará- Brasil

Abstract

Mangrove are transitional ecosystems between continental and marine environments. It’s widely distributed along the Brazilian coast, under great variability of climatic, oceanographic, geological and geomorphological conditions. In despite of the ecological, social and economic importance of the mangroves, the knowledge is little about the geological characteristics the knowledge is little about the geological characteristics and geochemical processes to the mineralogical changes that occur in the soils of these ecosystems in the coast of the state of Ceará. Soils mineralogy is an important input to the pedogenic processes and biogeochemical behavior of nutrients and potential inorganic and organic pollutants found there, such as trace metals. This study provides data on organic matter (OM), Calcium Carbonate (CaCO3), the levels of trace metals (Cd, Pb, Zn, Cu, Al and Fe), the composition of clay minerals and textural and sized analysis in two sediment cores (T01 and T02) located in the mangroves situated on the right bank of the Coreaú river. About the variety of coloration of the sediments core, it can be identified small variations between grayscale clear to darker shades of gray to brown, and yellow tones in T02. The diameter of the sediment from the samples showed a predominance of mud fraction on the other sized classes (fractions up to 99%), especially in T02 core, however it can be observed levels higher than 70% of the gravel and sand fractions at some points in the two sediment cores. The content of O.M. sediment ranged between 0,84% to 5,3% and CaCO3 7,2% to 27,1%, the metal contents in the profiles obtained were: Cd (content below the detection limit of the instrument to 1, 2 ppm), Pb (2 ppm to 19 ppm), Cu (1,8 ppm to 23 ppm), Zn (6 ppm to 72 ppm), Fe (6.673,0 ppm to 57.684,0 ppm) and Al (14.851,0 ppm to 107.103 , 0 ppm). The general analysis suggests that the contribution of metals in the area T02 is greater than T01 in the field also suggests a greater influence of human activity in this area. As for mineralogy, clay minerals identified were: smectite, kaolinite and iilita. The Assembly mineralogical didn’t change from one profile to another. This mineralogical uniformity reflects the presence of similar geochemical conditions in profiles.