Bacteriological study of the superficial sediments of Guanabara Bay, RJ, Brazil

Abstract

Thirty sediment samples were collected in Guanabara Bay in August, November and December 2005. The material was analyzed for organic matter, total and faecal coliforms, heterotrophic bacteria, bacterial respiratory activity, esterase activity and electron transport system activity. The organic matter in the superficial sediments (2 cm) ranged from 4 to 6%. The highest level of total coliforms and faecal coliforms were 1.7 × 105 MPN/g and 1.1 × 103 MPN/ g, respectively. Heterotrophic bacteria presented the highest values at station 7 (4.1 × 106 CFU/g) and the lowest values at station 3 (7 × 104 CFU/g) (northwestern part of Guanabara Bay). Esterase enzyme activity showed activity in the sediment of all 30 stations. Electron transport system activity ranged between 0.047 μL O2/h/g and 0.366 μL O2/h/g at six stations. The benthic microbial foodweb is anaerobic. Anaerobic processes such as fermentation, denitrification and sulphate-reduction are responsible for the biogeochemical cycles in the sediment of Guanabara Bay. The input of untreated sewage in the Mangue Channel outflow in Guanabara Bay has favored the increase of the organic load, and the maintenance of the total coliforms and faecal coliforms in the sediment. Faecal coliforms have been reported to be a good indicator of aquatic pollution and organic contamination in the water column, but total coliforms may be an ideal candidate group for sediment quality tests as well.