The Impact of Episodic Events on Nearshore-Offshore Transport in the Great Lakes:
Sediment Resuspension and Transport
B. Eadie, D. Edgington, B. Lesht, V. Klump, K. Nealson, J. Robbins,
and B. Tonner
Within systems, episodic events are essentially the drivers for a major set of processes that
control the biogeochemistry of coastal waters. Because of their erratic time dependence and
highly variable physical forcing, the role of episodic events on structuring coastal systems,
from their basic circulation to their biogeochemical cycles and ecology, is poorly known. The
reason is simple, episodic events are inherently difficult to study, and by definition difficult to
predict. The Great Lakes, and the Lake Michigan basin in particular, however, provide
representative systems in which the study of these types of events are in fact tractable.
Our conceptual biogeochemical/physical model is that new particles enter the lake, primarily
from shoreline erosion. Initially, these particles are transported into temporary sinks or
repositories within the coastal margin that are non-depositional in the long term (years to
decades), and are transported into temporary sinks. Large episodic events like the plume
event resuspend and transport these materials from these temporary sinks to more permanent
sinks with a small fraction becoming incorporated annually into the sediments of the
depositional basins. The majority are stored in transient reservoirs as part of the
biogeochemically important and active boundary layer. They are subsequently transformed
by numerous biogeochemical processes over an average of 20 years (mean residence time of
particle associated with the disappearance of long-lived fallout radionuclides and other
tracers).
During this period, these easily resuspendible sediments constitute the major dispersed source
of many biogeochemically important materials (BIMS) and contaminants to the pelagic
system, however (1) We do not understand the extent, time dependence and dynamics of
BIMS in the coastal margin system. (2) The repositories of sedimentary material in the system
are not confined to`depositional' environments, but must exist as a concentrated `floc' layer
at the benthic boundary throughout much of the system, particularly in the coastal margin.
(3) These temporary repositories play a key role in cross-margin sediment transport and in
the biogeochemical cycles of coastal systems in general and of the Great Lakes and Lake
Michigan in particular, from the dynamics of phosphate supply and primary production to
contaminant fate. (4) The residence time of new particles in these repositories depends upon a
`conveyor belt' of resuspension and redeposition moving particles both alongshore and
offshore. (5) We do not have a good understanding of the nature of the processes occurring
at particle surfaces as a result of diagenesis and biogeochemical transformations. This
research seeks to address these issues using a variety of in situ and laboratory techniques
designed to look at the fate and transformation of biogeochemically active particles in a
dynamic coastal system.