Microbial Activities and Bioavailable Concentrations of Cu, Zn, and Pb in Sediments from a Tropic and Eutrothicated Bay

Stressed communities show changes in energetics and nutrient demand and recovery. The evaluation of microbial communities energy demand can be measured by enzyme activities. Thus, by using such approaches, it might be possible to determine the microbial response to metal contaminations. Guanabara Bay surface sediments were sampled in 20 stations. Grain size, bioavailable metals, total organic carbon, total sulfur, dehydrogenase activity, esterase activities, viable bacterial cells, carbohydrates, lipids, and proteins were determined in all samples. Bioavailable metal concentration ranges from below detection limit in sandy stations in the entrance of the bay by up to the same order of magnitude as total concentrations obtained by other authors. Biopolymers were mainly lipids and carbohydrates, and minimum concentrations were also observed in sandy sediments. C: S ratio of 4.4 +/- 1.3 (mean +/- standard deviation) expresses the reduced tendency conditions of the bay, negatively correlated to viable bacteria cells (in order of 10(7) cell g(-1)). Esterase enzyme activities positively correlated with organic and fine sediment content. Stations with the highest metals and organic contents also have the highest esterase activities and dramatic decline of bacterial cells. In these locations occur better water renewal and subsequent aeration, which increases the efficiency of the organic matter oxidation and decreases matrix geochemical sequestration of metals and renders them bioavailable.