Influence of submarine sewage outfall in the sediment quality of São Sebastião channel (São paulo, br) through foraminiferal assemblages

Abstract

Benthic foraminifera are used as environmental bio-indicators, especially in polluted environments where their sensitivity to pollutants may be expressed by alterations of the assemblages. Eighty-one sediment samples were collected in nine sampling trips in spring and summer (October/98, January/99, November/00, November/01) and in autumn and winter (May/99, May/00, May/01, August/99 and July/02) in the São Sebastião Channel for the study of foraminiferal assemblages. This work is related to the monitoring of a submarine outfall, considering that it is subjected to oceanographic variations and anthropic influences. We intend to determine the quality of the interface sediment-water in the TEBAR (Almirante Barroso Maritime terminal, PETROBRÁS) through foraminiferal species indicator of vulnerable environments. Results show the large number of living organisms, young and adults reveal that water circulation and dynamics favor the establishment and development of well-oxygenated foraminiferal species explaining the absence of eutrophication caused by TEBAR and the urban sewage of São Sebastião and Ilhabela. However, the low number of species recorded along the São Sebastião channel is not normal for inner shelf. The number of species in the Channel is comparable to estuarine environments where freshwater limits the distribution of organisms. This low number of species could be attributed to some of the condition that results from the effects of various sources of contamination in the Channel, such as sewage from cities, harbor, TEBAR, primary surface runoff, hydrocarbon spills among others dividing the environment in two groups. The opportunist tolerant group: Ammonia spp., Buliminella elegantissima, Bulimina marginata, Bolivina striatula and Fursenkoina pontoni, proliferate where high organic matter indicates terrestrial contribution, anaerobic environments in the central regions of the Channel and should be used as bio-indicator of pollution. The second more oxygenated tolerant group includes Quinqueloculina spp., Elphidium poeyanum, Hanzawaia spp., Discorbis williamsoni, Discorbis floridana, Pyrgo sp., Cassidulina minuta, Cassidulina subglobosa and Pararotalia cananeiaensis, indicative of well-oxygenated environments, high dynamic currents in the region, and penetration of marine currents in the channel.