Frontiers in Marine Science (May 2014)
Development of an integrative approach for the characterization of environmental risk on marine transition ecosystems: the Sado estuary as a case study
Abstract
Estuaries and transitional waters are important ecosystems from which organisms and humans are dependent on for survival. They are important as nursery areas and shelter for many aquatic organisms, from which humans and their economical activities are dependent on. Humans also depend on estuaries for other reasons such as tourism, heavy industry, aquaculture and shipping. The degradation of estuarine environmental quality implies ecologic, economic and social prejudice, so it is important to evaluate the state of the environment to assist management. The Sado estuary (SW Portugal) is considered moderately contaminated. The area is impacted by diverse human activities, from shipping, industry, urbanism and even mariculture and agriculture activities. Because Sado estuary is very important for human and ecological reasons, many studies were conducted by several researchers in past few years, albeit scattered. As such, there was a need to integrate the information hitherto produced, in order to obtain a clear and complete image of the overall environmental quality status of the area, to assist future management plans and decision-making. For the purpose, a geographical information system (GIS) was created from sediment contamination and biomarker data collected from a decade-long time-series of publications. Five distinct areas were identified from the Sado estuary: a clean area plus four contaminated areas characterized by distinct sediment contamination patterns, related to different pollution hot spots and diffuse contamination sources. Also, in spite of the multiple biological traits under survey, the biomarker data (from several organisms) are in general agreement with the environmental contamination georeferencing information. Through this evaluation, the main anthropogenic sources of pollutants were identified, namely, the shipyard area and adjacent industrial belt, followed by urban and agricultural inputs into the estuary. From the data it is evident that the estuary, although globally moderately impacted, is very heterogeneous and affects by a cocktail of contaminants that includes metals, polycyclic aromatic hydrocarbon (PAHs), polychlorinated biphenyl (PCBs), dichloro-diphenyl-trichloroethane (DDTs) and others. Although many metals can come from the type of geology of the hydrographic basin from the upstream of the river, the majority of the remaining contaminants should result from human activities. The present work revealed that the estuary should be divided into very distinct management units, in accordance with its high biogeographical and ecotoxicological diversity in order to implement effective measures to safeguard and improve environmental quality.
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