Spatial and Temporal Variability in Nutrients and Suspended Material Processing in the Fier d'Ars Bay (France)

Abstract

A net material flux study in an estuarine mudflat along the French Atlantic coast, confirmed the general hypothesis already shown in European salt marshes. Despite its small area, the system was not as homogeneous as first thought. The upper part of the bay imported both dissolved and particulate matter, whereas the lower part exported dissolved and imported particulate matter. Tidal dynamics and water residence time were suspected of enhancing these differences. Particulate mineral import represented more than 70% of the total suspended sediment, with export of silicate, dissolved organic carbon and chlorophyll a. It is assumed that phytoplankton and microphytobenthos were exported from the bay in a degraded form. A wide synthesis was conducted integrating the tidal physical dynamics, with the geomorphology of the system, to explain material flux differences between the two sampling sites. Differences of particulate material transport between European and North American systems were verified. New hypotheses relative to the functional role of phytoplankton and microphytobenthos in coastal food chains in European salt marshes were also investigated. In contrast to American systems, mineral particulate import was prevalent in European ecosystems, enhancing growth of small-celled phytoplankton and microphytobenthos. These latter, were sorbed onto sedimenting mineral particles, thus limiting losses from estuaries and explaining the major particulate retention in these systems.