The Gironde estuary

This article synthesizes sedimentological and geochemical research conducted on the Gironde estuary up to 1978. The estuary, part of the Aquitaine Basin, spans about 80,000 km² and is characterized by a temperate oceanic climate. It results from the confluence of the Garonne and Dordogne rivers. Local industrial development remains limited, preserving the estuary's ecological balance. The article details various ecological aspects, noting that water pH ranges from 7.4 to 8.5, with dissolved oxygen saturation fluctuating between 10 and 130 o/oo, particularly seasonally. Nutrient changes are linked to upstream dilution and organic matter oxidation. High trace metal levels are observed upstream, decreasing significantly downstream, where heavy metal concentrations align with global averages in minimally polluted environments. This reduction in metal concentrations in suspended particulate matter is attributed to the solubilization of metals from these particles. To clarify these mechanisms, advanced methods, including double tagging with radioactive isotopes and chemical sequential extraction, were employed. The Gironde estuary serves as a valuable resource for estuarine studies and for assessing substance transfer at the continent/ocean interface.