“Sediment’s Quality Responders”: Water Renovation, Sewage and Industrial Pollution Stress on Benthic Fauna

Abstract

Analyses of living foraminiferal and environmental parameters near an outfall at Mar Grosso Beach (Laguna, SC, Brazil) demonstrate its usefulness as indicators of domestic sewage pollution. The low species diversity may be due to sand accumulation in the surf zone of the central part that prevents settlement on or in the substrate. Silt and clay content correlates well with the total coliforms higher diversity of foraminiferal species, reduced salinity, and higher temperatures closer to the mouth of Laguna estuarine system indicate freshwater influence, suggesting relationship between increased diversity and greater availability of terrestrial food, even if the salinity decreases. Higher Forams diversity and average coliform values are closer to the mouth of the estuarine system and under the influence of the outfall. The estuary mouth is under the influence of the outfall and exhibits higher foraminiferal diversity and higher mean values of total coliforms and silt-clay content. Due to the effect of local hydrodynamics, the particulate organic waste derived from the outfall settle down locally, accumulating nearby on the southwestern and northwestern parts of the beach. We confirm our hypothesis that the fine material derived from the outfall is accumulating in shallow parts of the beach. In general, the characteristics of the foraminiferal assemblages show that the environment is in the initial stages of eutrophication. Apparently, the nutrient enrichment of the water by the organic waste has induced changes in the benthic foraminiferal community through an increase in species richness. Due to the high energy of the marine environment, however, the particulate organic waste derived from the outfall does not settle down on the seabed; but it supports the hypothesis that the fine material derived from the 12-m deep outfall is accumulated on the southwest part of the beach.

The fluctuations in salinity and temperature in Todos os Santos Bay established different tolerance limits for certain species, which indicates that species distribution was subject to natural environmental seasonal changes and excellent water renovation. In the present study, many marine species were observed, indicating a strong influence due to intrusion of marine waters from the adjacent continental shelf. Given that, opportunistic-tolerant species directly benefit from certain kinds of contamination of organic substances, or indirectly, through the reduction of competition and predation, increasing their local occurrence; this chapter reveals this bay as an environment where organic matter is easily deposited, the excess of nutrients results in a low diverse fauna dominated by Ammonia spp. closer to freshwater sources.

The occurrence of Elphidium spp. and Quinqueloculina spp. is limited to the eastern part of the TSB. Pseudononion atlanticum and Bolivina spp. presented their occurrence limit in the area under continental runoff influence. A decrease in diversity indicates less stability close to Mataripe River and RLAM area, and an increase in diversity in central and east parts of Todos os Santos Bay. Some areas present aliphatic accumulation, and silt and clay accumulation. Ammonia tepida, Bolivina spp., and Fursenkoina pontoni tolerate sediment with aliphatic and unresolved complex mixture, while Elphidium spp. decreases in areas under the influence of pollutants. Ammonia spp., Bolivina spp., and Fursenkoina pontoni are known organic matter and low oxygen-tolerant foraminifers, and in the bay, they are tolerant to petroleum derived pollutants.