J. Phys. IV France 107 (2003) 1071 (D EDP Sciences, Les Ulis DOI : 10. 1051/jp4 : 20030485 Trace metals inputs in the Adour urban estuary : Influence and impact of human pressure D. Point, G. Bareille, T. Stoichev, D. Amouroux and O. F. X. Donard Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, UMR 5034 du CNRS-UPPA, Hélioparc Pau Pyrénées, 64053 Pau, France Abstract Although the contamination of number of estuarine environments in the European Atlantic Coast has largely been studied 11-2], 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 evatuate and quantify the anthropogenic pressure on the ecosystem. A preliminary sampling strategy approach 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, 45pin) 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 1. INTRODUCTION Estuarine environments are some of the most productive ecosystems known, and very sensitive to trace metals pollution. Anthropogenic trace metals fluxes, are discharged in the estuarine environment in various forms (filtrate and/or particulate phase) and in different concentrations, generating also diffuse or chronic contamination effects. Typically limited estuarine data are available according to trace metal sources, characteristics and fluxes. This lack of knowledge is also enhanced by the numerous inputs of contaminants from point and non-point sources [3], so it is very important to define and to estimate trace metal pollution fluxes associated with. The Adour estuary is an important urban (industrial and harbour activities) macrotidal estuary located in the south-westem of France and is flowing into the Gulf of Biscay (Atlantic Ocean). The focus of this study is mainly on watershed inputs represented by Adour, Gaves and Nive rivers and anthropogenic inputs according to point and non point sources largely distributed along the estuary ; both being sources of trace metals to the estuarine mixing zone (salinity intrusion). 2. METHOD 2. 1 Area description The Adour estuary (fig. 1) is a collection of waters from a whole drainage basin (16. 380 Km2), including the Adour, " Gave d'Oloron " and " Gave de Pau " rivers (referre as Adour upstream inputs in the following). The Nive river (considered as another upstream source) is connected to the estuary close to its mouth. The annual average Adour upstream discharge is 250 nz3. s'l (varying from 50 m3. s~l in summer