• Citer

Nutrients (organic C, P, N, Si) in the eutrophic River Loire (France) and its estuary

par Meybeck, M.;Cauwet, Gustave;Dessery, Sophie;Somville, Martine ;Gouleau, Dominique;Billen, Gilles
Référence Estuarine, coastal and shelf science, 27, 6, page (595-624)
Publication Publié, 1988-12

Article révisé par les pairs

• Accès en ligne
• Détails
• Contenu
• Statistiques

Résumé :

The Loire estuary has been surveyed from 1982 to 1985 by 13 isochronous longitudinal profiles realized at low tide. Nutrient (SiO2, NO3-, NH4+, PO3-4, particulate organic carbon or POC) patterns are very variable depending on the season, the estuarine section [river, upper-inner estuary, upstream of the fresh-water-saline-water interphase FSI, the lower-inner estuary characterized by the high turbidity zone (HTZ), the outer estuary] and the river discharge. Biological processes are dominant. In the eutrophied River Loire (summer pigment > 100 μg l-1), the high algal productivity (algal POC > 3 mg l-1) results in severe depletion of SiO2, PO43-, NO3-. The enormous biomass (55 000 ton algal POC/year) is degraded in the HTZ where bacterial activity is intense. As a result, there is generally a regeneration of dissolved SiO2 and PO43-, a marked NH4+ maximum, while NO3- is conservative or depleted when the HTZ is nearly anoxic. Other processes can be considered including pollution from fertilizer plans (PO43-, NH4+) and from a hydrothermal power plant (NH4+). In the less turbid outer estuary, nutrients are generally conservative. Major variations of concentrations are observed in the lowest chlorinity section (Cl- < 1 g kg-) and also upstream the FSI, defined here as a 100% increase in Cl-. Nutrient inputs to the ocean are not significantly modified for SiO2 and NO2-, but are increased by 70% and 180% for PO43- and NH4+ and depleted by 60% for POC. Odd hydrological events, especially some floods, may perturbate or even mask the usual seasonal pattern observed in profiles. © 1988.