generally required a few months but was much longer for gastropods. Sweeney 

 (1978b) noted near recovery in i yr, but the community structure was altered. 

 There was an increase in oligochaete abundance along with decreases in many 

 other common groups (e.g., nematodes, chironomids, and isopods). Several pol- 

 lution tolerant species became abundant within and near the disposal areas. 



The ultimate impect of contaminants associated with dredged material dis- 

 posed in deepwater ecosystems is still unresolved. Tainting of certain ben- 

 thic organisms by oils, greases, and phenols is known to occur (Sly 1977). 

 Disposal of dredged material in the deep waters of the Great Lakes does not 

 appear to influence water circulation as much as disposal in constricted ma- 

 rine estuaries. Danek et al. (1S77) noted buildups of deposited material in 

 mounds of up to 45 cm (18 in) high but a severe storm later eroded much of the 

 new sediments. 



Habitat Development 



Compared to marine environments, little work has been done with habitat 

 development in the Great Lakes, consequently much of the discussion in this 

 section is untried ideas or random observations rather than documented stud- 

 ies. 



Terrestrial development . The reader is referred to Part III - Coastal 

 Waters. 



Island development . Colonial nesting sea and wading birds have made good 

 use of dredged material islands in the Great Lakes (Sharf 1978). Natural nest- 

 ing sites were in short supply. 



Another apparent beneficial use for dredged material islands in the Great 

 Lakes is for protecting nearby shore areas from wave action. Islands will pro- 

 tect shallow-water areas and allow the development of marshes or protected 

 fish spawning and nursery areas (personal communication, 4 December 1975, 

 Richard Hoppe, FWS, Green Bay, Wisconsin). 



Wetland development . The reader is referred to Parts III and IV - Coastal 

 Waters and Rivers for discussions that may be adapted to the Great Lakes. 



Aquatic development . Dredged material has sometimes provided mounds or 

 irregular substrates around which fish concentrate and are utilized for spawn- 

 ing in the Great Lakes (personal communication, 1 December 1975, Thomas Yokum, 

 FWS, Ann Arbor, Michigan). Large portions of the Great Lakes have smooth 

 unvarying bottoms with fine sediments. These areas neither attract and con- 

 centrate fish, nor provide spawning areas. The construction of artificial 

 spawning reefs for species such as lake trout and walleye appears to be a pos- 

 sible use of dredged material. However, since most dredged sediments are fine 

 grained, topdressing with some type of coarse material would likely be neces- 

 sary. Also, the toxicity of dredged material is a major consideratlor. Rela- 

 tively clean materials would have to be used. 



79 



