A series of cruises was carried out in the estuarine turbidity maximum (ETM
) region of Chesapeake Bay in 1996 to examine physical and biological varia
bility and dynamics. A large flood event in late January shifted the salini
ty structure of the upper Bay towards that of a salt wedge, but most of the
massive sediment load delivered by the Susquehanna River appeared to bypas
s the ETM zone. In contrast, suspended sediments delivered during a flood e
vent in late October were trapped very efficiently in the ETM. The differen
ce in sediment trapping appeared to be due to increases in particle settlin
g speed from January to October, suggesting that the fate of sediments deli
vered during large events may depend on the season in which they occur. The
ETM roughly tracked the limit of salt (defined as the intersection of the
1 psu isohaline with the bottom) throughout the year, but it was often sepa
rated significantly from the limit of salt with the direction of separation
unrelated to the phase of the tide. This was due to a lag of ETM sediment
resuspension and transport behind rapid meteorologically induced or river f
low induced motion of the salt limit, Examination of detailed time series o
f salt, suspended sediment, and velocity collected near the limit of salt,
combined with other indications, led to the conclusion that the convergence
of the estuarine circulation at the limit of salt is not the primary mecha
nism of particle trapping in the Chesapeake Bay ETM. This convergence and i
ts associated salinity structure contribute to strong tidal asymmetries in
sediment resuspension and transport that collect and maintain a resuspendab
le pool of rapidly settling particles near the salt limit. Without tidal re
suspension and transport, the ETM would either not exist or be greatly weak
ened. In spite of this repeated resuspension, sedimentation is the ultimate
fate of most terrigenous material delivered to the Chesapeake Bay ETM. Sed
imentation rates in the ETM channel are at least an order of magnitude grea
ter than on the adjacent shoals, probably due to focusing mechanisms that a
re poorly understood.