Research Brief:
Technical Evaluation of Suspended Sediment Effects
on Biological Resources

Issue     

Environmental concerns have arisen that suspended sediment concentrations resulting from dredging and disposal plumes can reduce viability of fish eggs, growth and survival of larval and early juvenile fish, growth and survival of bivalves, and movement of larval fish and shellfish into nursery areas from offshore waters. Hypothetically, these effects can occur in several ways, most notably from deposited sediments smothering animals, suspended sediments reducing feeding abilities, or suspended sediments being raised above sensitive life history stage physiological tolerances. The extent to which these observations are likely to occur in the field is unclear. Because relevant field studies have not previously been conducted, resource agencies act conservatively by limiting dredging to months when impacts are theoretically minimal. Ambiguity in the data used to support windows fosters conflict during dredging project coordination.

Research/Objectives    

An objective of this research is to characterize the distribution, growth, and survival of larval fish and shellfish in the field and laboratory in the presence and absence of actual or simulated dredging and disposal plumes. This research is also characterizing the transport of larval and juvenile fishes through and around dredged material plumes to determine if plumes act as a barriers or significant sources of stress to these organisms. Precisely defining parameters to be measured in the field requires laboratory testing to fill gaps that presently exist in the literature. Active dredging projects in areas where environmental windows are most restrictive will be examined to compare the abundance and species composition of larval fish and shellfish within and outside dredging-induced plumes. Growth increments of selected larval fish and juvenile shellfish will be determined, and growth rates in the presence and absence of dredging, vessel traffic and storm-induced plumes compared. This information will be integrated into bioenergetic and population dynamics models so consequences of exposure to plumes can be accurately predicted and appropriate guidance to minimize unacceptable impacts developed. A decision framework for protection of critical life history stages by means of technically justified environmental windows will be prepared.

U.S. Army Engineer Research and Development Center

September 2001
www.erdc.usace.army.mil
www.wes.army.mil/el/dots/doer

Results/Products     

Research Team