Qualit� des eaux en milieu estuarien: Suivi annuel de crit�res physiques et chimiques dans les eaux de l'estuaire de la Loire

Abstract

Chemical composition and physical parameters of waters from the Loire estuary were examined in 1981–1982 in order to assess water quality. It appears that riverflow is of first importance on suspended matter load, dissolved nutrient concentrations and oxygenation. The annual hydrological cycle is made of two periods. During the first one low riverflow, low nutrient concentrations, high suspended matter load and oxygen depletion are noticed. During the second one higher riverflows occur accompanied with increasing nutrient concentrations, decreasing turbidity and restoration of dissolved oxygen. Results indicate that annual inputs of dissolved nutrients attain 60 000 t a−1 for nitrogen, 2 400 t a−1 for phosphorus and 100 000 t a−1 for silica. It is suggested that the high suspended matter loading (1 million t a−1) is a significant factor disturbing oxygenation and by the way limiting water quality within the estuary.