VI. C. 3. Impacts - Physical Processes and Biological Considerations |
Disruption and displacement of benthic communities is an unavoidable impact of dredging, although recolonization generally occurs within 3 to 5 years (Williams et al. 2001). Benthic habitat characteristics, such as elevation and grain size, can be changed by dredging and alter the original biological community. Benthic or demersal fishes, such as sand lance, sculpins, and pricklebacks, are particularly susceptible to dredge entrainment (Nightingale and Simenstad 2001a), and the loss and disturbance of benthic communities can affect food-web interactions. Elevated turbidity levels have been shown to affect fish behavior, such as avoidance responses, territoriality, and feeding and homing (Nightingale and Simenstad 2001a). Dredging and shoreline construction activities can also disrupt migration pathways of juvenile salmon as a result of loud inconsistent noises, water turbulence, and other associated obstructions (Pacific States Marine Fisheries Commission 2001).
One potential environmental impact of dredging in nearshore areas is a temporary increase in turbidity from sediment resuspension, which may reduce dissolved oxygen and can also adversely affect fish and other aquatic species. While mechanical dredging generally maintains most of the dredged material in the bucket in a cohesive clump, some sediment loss and resuspension into the water column occurs. Because marinas are protected from strong currents and have reduced water circulation, the majority of suspended sediment generated in marina dredging projects likely remains in the immediate vicinity. Although the effects of dredging on nearshore habitats and species are known in a general sense, few quantitative data link dredging to changes in habitats and species.
Filling immediately alters the bathymetry and topography at the site and can also bury or displace existing organisms (Williams and Thom 2001). In cases where the change in bathymetry or topography is substantial, these organisms may not be able to recolonize a site, and historic opportunities offered by the site (e.g., forage fish spawning) are lost. Filling may substantially change beach profiles, marsh channel morphology, and habitat connectivity. If fill materials are different from the original substrate at the site, changes in sediment types and/or sizes will influence the composition of local plant and animal communities. In general, few long-term studies have specifically examined how historical fill activities change biological resources and functional interactions.
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