Résumé
Guia marine outfall is the largest sewage discharge system in Portuguese waters. It serves four municipalities and a population of approximately 600,000 inhabitants. Effluent diffusion occurs approximately 3 Km from the shore, at a depth of 40 meters. Operation of the outfall was initiated in May/June 1994 and, at present, does not include secondary treatment, or conventional primary treatment.
In March 1994, before operation of the outfall, an integrated monitoring program was designed, which included a baseline sediment survey. Environmental chemistry, macrofaunal benthic communities and laboratory sediment toxicity analyses were performed in sediments from 20 sampling sites. These sites were revisited 3 and 4.5 years later in order to evaluate any changes to the sediments and their associated biota. This paper presents the results obtained from those two sampling periods, and proposes a classification for the evolution of sediment status. It also addresses the need or not to introduce, at present, more elaborate effluent treatment methods.