This software is used in-house by ASA and is not available for commercial distribution.

Suspended Sediment Exposure Model: SSDOSE

SSDOSE calculates exposures of various aquatic organisms to sediment plumes resulting from dredging operations and analogous sediment releases. SSDOSE uses the output from SSFATE that includes concentration of suspended sediments as a function of space and time. SSDOSE is contained in the SSFATE graphical user interface system, allowing the user to readily work with both models to produce and view results. Using the models, the user is capable of examining alternative dredging practices and providing insights into risk minimization.

One way to evaluate potential impacts on aquatic biota and habitats marine biologists is to determine the exposure level of aquatic organisms to elevated sediment concentrations. Previous research has shown that effect is related to both concentration and duration of exposure. Thus, the SSDOSE extension for SSFATE quantifies the dose to aquatic biota.

Dose is defined as the sum over time of suspended sediment concentration times duration of that exposure. Dose is related to the location over time of the organism or habitat relative to the suspended sediment plume. Thus, the pathway of movement (if any) of the organism needs to be simulated and the exposure along that pathway summed to quantify dose. The exposure model in SSDOSE tracks the movements of organisms through the water and over time, calculating dose and mortality based on toxicity of the concentration and duration of exposure (if toxicity data are provided). Mortality is first calculated as a percent of organisms in the area. This percent loss may be multiplied by abundance to estimate biomass lost.

Within SSDOSE a variety of movement behaviors can be simulated. Categories include: passively drifting plankton (e.g., buoyant fish eggs), stationary on the bottom (e.g., demersal eggs), stationary in the bottom (e.g., benthos or plants, with exposure calculated as sediment loading or mass per unit area), pelagic non-directed movement (e.g., slow random movement of small fishes or rapid random movement of large fishes), non-directed movement just above the bottom (e.g., demersal fishes), pelagic directed movement (e.g., at a speed and path specified by the user, as could be used for anadromous fishes), and demersal directed movement (e.g., at a speed and path just above the bottom specified by the user, as could be used for certain crustaceans). Because habitat maps can be structured within the model's habitat grid, movements of taxa categories can be restricted within specified areas. This feature allows simulation of site tenacious species. SSDOSE outputs include tabulations of dose for each movement behavior category and percent mortality by each behavior category. Also produced are animated maps of the locations of exposed organisms over time and locations of mortality over time. Both types of maps depict color-coded symbols representing magnitudes of dose and mortality.

For more information on SSDOSE, please contact by email: Craig Swanson

SSDOSE is under development with the U.S. Army Corps of Engineer Environmental Research and Development Center. If you have any questions or are interested in our services please contact us.