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ERDC TN-DOER-E9
May 2000
Assessment of Potential Impacts
of Dredging Operations Due
to Sediment Resuspension
PURPOSE: This technical note summarizes the known biological responses of estuarine and
coastal fish and shellfish to suspended sediments and relates these findings to suspended-sediment
conditions associated with dredging projects. An objective approach toward evaluation of sediment
resuspension impacts is proposed that requires full consideration of (a) the existing state of
knowledge concerning the effects of suspended sediments on fish and shellfish, including recogni-
tion of the gaps therein, and (b) concentration-exposure duration combinations likely to be
encountered by organisms in the vicinity of dredging operations. This note focuses upon the
exposure of organisms to sediments in the water column. Effects of deposited sediments will be
treated separately.
INTRODUCTION: Estuarine and coastal organisms are exposed to suspended sediments from
storms, tidal flows, and currents and therefore have behavioral and physiological mechanisms for
dealing with this feature of their habitat. Because dredging-related suspended-sediment plumes
may differ in scope, timing, duration, and intensity from natural conditions, dredging may create
conditions not typically experienced by resident or transient species. Assessing how dredging-
related suspended-sediment conditions may affect organisms requires knowledge of (a) the thresh-
olds at which relevant life history stages of organisms respond negatively to suspended
sediments, (b) reliable estimates of dredging-induced suspended-sediment plume temporal and
spatial dynamics, and (c) the probability that organisms encountering a dredging-related suspended-
sediment plume will exceed a concentration and/or exposure duration tolerance threshold.
The literature concerning suspended-sediment effects on aquatic fauna has been periodically
reviewed (e.g., Morton 1977; Moore 1978; Priest 1981; Kerr 1995). However, until recently, there
has been little attempt to assess environmental impacts with models that can be easily used by
resource managers (Newcombe and MacDonald 1991). Simplified models have been developed to
predict suspended-sediment impacts on freshwater fishes (Newcombe and MacDonald 1991;
Gregory, Servizi, and Martens 1993; MacDonald and Newcombe 1993) and were expanded to
include estuarine fishes (Newcombe and Jensen 1996). Historically, suspended-sediment impacts
were considered to be a function of concentration; i.e., most experimental studies used concentration
alone as the variable of interest, and exposure durations were not varied and in many cases not
reported (Sherk and Cronin 1970; LaSalle et al. 1991). Regulatory controls on suspended-sediment
impacts also focused on concentration thresholds. More recently the duration of exposure to
suspended sediments has been emphasized as another important factor. Concentration alone is
poorly correlated with the responses of salmonid fish to suspended sediments, whereas dosage
(measured as mg h l-1) is more strongly associated with fish responses (Newcombe and MacDonald
1991).
Newcombe and Jensen (1996) recognized the utility of "look-up tables" that can be used in the field
or as an easy reference to predict suspended-sediment impacts on biological resources. This

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