Matéria organica particulada e atividade bacteriana nos sedimentos superficiais da Baía de Guanabara, no Rio de Janeiro, Brasil

Abstract

The aim of this work was to analyze bacterial esterases enzymes associated with the organic particulate, which gets to the superficial sediments of the Guanabara Bay, in Rio de Janeiro, Brazil. Thirty samples of superficial sediment were collected, in which grain size, total organic carbon, sulfur, activity of the esterases enzymes, and particulate components of organic matter under microscopy were analyzed. The results had shown that the textural class was between 62.65 to 85.63% for silt, 7.51 to 12.87% for clays, and 4.46 to 29.59% for sand. The average total organic carbon (TOC) and sulphur (S) were 3.78 and 0.77%, respectively. The highest esterases value was found in station 18 (4.69 μg fluorescein/h/g) and the lowest in 24 (1.25 μg fluorescein/h/g). The average of activities was of 3.20 μg fluorescein/h/g. The palynofacies analysis showed a predominance of the amorphous (82.4%), palynomorphe (9.2%), and phytoclast (8.4%) organic matters. The amorphous organic matter is predominant in all samples and the esterases enzymes activities are associated with the silt-clay. The palynomorphes are associated with sand. Cuticles, sporomorphes, and Botryococcus are directly related to to fluvial fluxes of rivers. The combined results of the analyses on organic geochemistry (elementary analysis) and microscopical techniques (transmitted and fluorescence light) disclose organic facies, with predominance of amorphous organic matter. The intense fluorescence coloring, together with raised value of total organic carbon (>6%) indicate high rate of preservation and low content of free oxygen in the environment. These results correspond to an organic facies, like marine shale, which is a characteristic of a deposited facies under persistent anoxic water column with anaerobic microbial activity.