Heterotrophic bacteria abundances in Rodrigo de Freitas Lagoon (Rio de Janeiro, Brazil)

Abstract

The Rodrigo de Freitas Lagoon (RJ, Brazil) is an important coastal ecosystem that has been submitted to an accelerated degradation process. The aim of this work was to determine the abundance and the spatial distribution of total heterotrophic (by flow cytometry) and cultivated bacteria ("pour plate" method on R2A agar). Another objective was to evaluate the lagoon's influence on water quality of Ipanema and Leblon beaches. Physical and chemical data were acquired too. Sub-superficial water samples were taken monthly, from December 1999 to October 2000. On lagoon, the cultivated bacteria abundance varied from 6.9×105 to 5.0×107 CFU.100 mL-1. On Ipanema and Leblon beaches, this parameter yielded 1.4×105 and 2.8×106 CFU.100 mL-1, respectively. Total bacterial abundance varied from 2.9×107 to 3.2×107 cells.mL-1 on lagoon. On Ipanema and Leblon, this parameter yielded 8.7×106 and 1.1×107 cells.mL-1, respectively. Two sub-groups were determined with dominance of HNA cells. Samples were added latter to better understand the bacteria present on these environments. Bacterial abundance were analyzed only by flow cytometry and the results varied from 8.3×106 to 2.5×107 cells.mL-1 on lagoon. On the beach, this parameter yielded 6.9×106 cells. mL-1. Two bacterial subgroups were also observed, with dominance of HNA on lagoon and LNA on the beach. The results showed that the Rodrigo de Freitas Lagoon is an eutrophic ecosystem where the bacterial populations and the physical and chemical parameters do not differ spatially. The data also confirmed that the outflow of the lagoon's polluted waters affect the sanitary conditions of Ipanema and Leblon beaches.