Structure, fonctionnement, évolution des communautés benthiques ...

tel-00009359, version 1 - 1 Jun 2005
Chapitre 3 - Fonctionnement du réseau trophique benthique de la Grande Vasière
The suspended particle distribution in station G showed a different pattern on September 18,
with clear temporal variations in the last 40 meters (Fig. 3): near-bottom particle load was highest at
low tide, while re-suspension was highest at mid ebb-tide. By contrast, particle load in bottom waters
was lowest at mid-flood. Maximum TPM flux was recorded when bottom-water particle load was
minimum (Fig. 3 and 9), and there was no apparent relationship between suspended particle
concentration in bottom water, as measured by the particle size analyser, and sedimentation rates (Fig.
9). On the other hand, hourly TPM sedimentation peaks in samples No. 3, 5 and 7 were clearly
associated with high-turbidity events recorded by the Sea-Tech light scattering sensor at the trap
aperture (Fig. 9). This result highlights the importance of continuous parameter recording when
addressing processes presenting high-frequency variability (5 PSA profiles were made on the 12-hours
period). The fourth high-turbidity event recorded between 5:00 and 6:00 PM was not associated with a
sedimentation peak, likely because current velocity (≥ 10 cm.s -1 ) at that time was to high. The same
trends as in spring were observed for late summer sedimentation dynamics after high tide, that is
decreasing TPM sedimentation rates with increasing bottom current velocity during ebb-tide (Fig. 9).
Overall, hourly TPM fluxes in bottom traps on 18 September varied in the same range as the one in
May (2- to 4-fold variations between 5 and 20 g.m -2 .h -1 ).
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