B ottom Impacts . The potential impact of dredged material disposal on or- 

 gan isms~TTvTngorror near the bottom is greater than potential impacts in the 

 water column. Impacts associated with the presence of dredged material on the 

 bottom include: (a) smothering and burial of organisms; (b) long-term changes 

 in species diversity and biomass; (c) uptake of toxic organic compounds; (d) 

 heavy metals uptake; (e) changes in water circulation; and (f) changes in sed- 

 iment size and movement. 



Sedimentation from disposal of dredged material can have strong negative 

 impacts when the settling occurs in an area containing sensitive organisms. 

 Areas of concern include coral reefs, seagrass beds, oyster reefs, and fish 

 spawning or nursery areas. Sedimentation can also be a source of nutrients. 

 Odum (1963) found an initial depression in productivity of Thalassia and 

 Diplanthera because of sedimentation from dredging. However, in the following 

 spring, high production values were exhibited by those beds not directly 

 smothered by the dredged material. Increased productivity was attributed to 

 the release of nutrients from the dredged material. 



Fluid mud is mainly generated by pipeline dredges and can flow along the 

 bottom driven by gravity or tidal currents (O'Neal and Sceva 1971). According 

 to Masch and Espey (1967), silt and clay particles make up 80% or more of the 

 total particulate matter of fluid mud. Benthic organisms are destroyed when 

 fluid mud separates them from the overlying water upon which they depend for 

 respiration and food (Diaz and Boesch 1977). 



Due to a lack of studies, information about the recovery time from fluid 

 mud impacts is not well known. Recovery in the tidal area of James River, Vir- 

 ginia, was nearly complete in 3 weeks but some adjustments were still occur- 

 ring after 3 mo. Other less resistant or resilient communities would probably 

 require a much longer recovery period (Diaz and Boesch 1977). A long-term 

 potential impact of fluid mud is the later resuspension of sediments into the 

 water column, thus increasing turbidity. 



Organisms buried by more consolidated materials will require a longer in- 

 terval to recolonize than organisms impacted by fluid mud. Recovery times for 

 sites buried by consolidated materials have been reported to require from a 

 few weeks to 2 yr or more. In many instances, predisposal assemblages of orga- 

 nisms will not reoccur if the substrate is altered by the addition of dredged 

 material that is substantially different from the substrate covered. The new 

 fauna may reach the original biomass but often will consist of different spe- 

 cies. The greatest impact occurs when unlike material is deposited, i.e., sand 

 on mud or visa versa. Polluted materials will retard recolonization indefin- 

 itely (O'Neal and Sceva 1971). Fine-grained materials are usually recolonized 

 more rapidly than coarse-grained materials. One study of relatively clean 

 dredged material in Rhode Island Sound indicated that after a recovery period 

 the faunal assemblage was diverse, abundant, and contained species valuable as 

 fish food (Saila et al . 1972). 



Bingham (1978) reported on recovery of benthic organisms at a deepwater 

 disposal site for contaminated dredged material in Puget Sound, Washington. 

 The following observations were made: 



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