material over a large area? This question will not be answered here, however, 

 Reimold et al.(1978) provide some insight into the ability of marsh to recover 

 from various depths of dredged material cover. In a Georgia salt marsh, 

 Spartina alterni flora nade substantial recovery from burial by up to 23 cm 

 (9 inches) of several types of dredged material. Reimold et al . (1978), how- 

 ever, urged caution in spreading dredged material on marshes and noted that 

 deposition should not result in a higher elevation than the surrounding marsh. 



Estuarine Disposal 



Estuaries are highly productive, complex systems and the potential for 

 damage by dredging is great. The potential for damage from aquatic disposal 

 appears to decrease as the disposal site is moved seaward from estuaries to 

 the continental shelf or into the deep ocean because biological productivity 

 and usefulness decrease while dilution and mixing increase (Pequegnat et al . 

 1978). Routine disposal of maintenance material (unless it is grossly pollut- 

 ed) is similar to other man-made and natural disturbances in impact to bottom 

 fauna. Benthic fauna living in or near navigational channels are well adapted 

 to such disturbance (McCauley et al . 1977). 



Water column impacts . Real or suspected impacts are associated with 

 suspended solids, release of contaminants, nutrient and biostimulant release, 

 destruction of plankton or nekton through physical contact with dredged mate- 

 rial, interference with animal migrations, dissolved oxygen depletion, and 

 toxic organics. 



Direct destruction of plankton and nekton is of little consequence be- 

 cause of the great reproductive capacity of plankton and because nekton can 

 usually avoid dredged material being deposited. 



The severity of water column impacts is strongly related to the degree of 

 dilution and mixing experienced. It appears that the potential impacts listed 

 above are not likely to adversely impact the water column in well-mixed wa- 

 ters. No adverse impacts were noted at four disposal sites in well-mixed 

 waters intensively monitored by the DMRP (Wright 1978), 



With the exception of fluid mud, suspended solids or turbidity from 

 dredged material disposal are not usually a serious problem (Hirsch et al . 

 1978). Fluid mud has been arbitrarily defined as sediment with a bulk density 

 of less than 1.3, a high water content, and suspended concentrations higher 

 than 10 g/1 (Nichols et al . 1978). Fluid mud and other adverse impacts of sus- 

 pended particles are discussed in the section about bottom impacts. Turbidity 

 generated by maintenance dredging has a visual or aesthetic impact but appears 

 to be short-lived and of less magnitude than turbidity from natural occur- 

 rences such as storms or floods (May 1973b, Markey and Putnam 1976, Schroeder 

 et al. 1977). 



Peddicord (1976: 606) made the following comment: "Undermost conditions 

 suspended particles themselves are lethal only at concentrations higher than 

 normally created by dredging operations, with important possible exceptions. 



iln this section we mainly discuss acute impacts of toxicants. For a discus- 

 sion of chronic impacts see "bottom impacts." 



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