Trace metals inputs in the Adour urban estuary: Influence and impact of human pressure
Résumé
Although the contamination of number of estuarine environments in the European Atlantic Coast has largely been studied [1-2], the Adour urban estuary watershed (southwestern, France) is poorly known. The estuarine part is characterized by an important anthropogenic pressure close to its mouth with large urban and industrial activities of Bayonne city. An environmental assessment program was funded to evaluate and quantify the anthropogenic pressure on the ecosystem. A preliminary sampling strategy was adopted to identify 25 specific sources of contaminants, monitored more extensively under four campaigns. Data treatment allows to trace effluent source and origin resulting in a specific classification. Trace metal concentrations were determined (filtrate (<0, 45 μm) and particulate fractions) for each effluent and combined with discharge flow measurements to establish anthropogenic net fluxes. Industrial effluents presents the highest concentrations observed, followed by waste landfield drainage and sewage effluents. The large variability in terms of effluent characteristics and concentrations observed, can be explained by strong relationship between trace elements and both organic matter level (TOC) and flow rate. This study point out the dominance of upstream inputs compared to downstream localized sources, but their influence into the estuarine ecosystem during low discharge conditions (summer) lead to a maximum metal impact.