Structure, fonctionnement, évolution des communautés benthiques ...

tel-00009359, version 1 - 1 Jun 2005
Chapitre 3 - Fonctionnement du réseau trophique benthique de la Grande Vasière
2002, sediment re-suspension was observed for a mean current speed of ca. 9 cm.s -1 at 1.6 m off the
bottom.
On the northern part of the muddy bank (Stn. G), the particle load distribution on May 3 rd
(neap tides) did not show any obvious temporal variation in the last 50 meters on a 12-hour period, but
suspended particle concentration appeared to increase regularly with water depth (Fig. 3). However, a
different pattern was observed for particle sedimentation (Fig. 9), with TPM fluxes in bottom traps
presenting low values (5 g.m -2 .h -1 ) from high tide to mid ebb-tide (from 8:00 AM to 1:30 PM),
increasing sedimentation rates (up to 20.7 g.m -2 .h -1 ) from mid ebb-tide to low tide, and decreasing
sedimentation rates during the flood (with again 5 g.m -2 .h -1 at mid flood). As for Station A,
sedimentation rates increased suddenly for mean current speed higher than 7 cm.s -1 , thus emphasizing
a critical threshold for particle downward flux or sediment erosion and re-suspension. Overall, 2- to 4fold
variations were observed for hourly TPM fluxes in bottom traps on May 3 rd .
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