APPENDIX 



GREAT LAKES^ 



ASSESSMENT OF IMPACTS AT THE DREDGING SITE 



W ater Column Impacts 



Sly (1977) summarized dredging studies on the Great Lakes (with emphasis 

 on Canadian waters) in which significant but short-lived increases in phospho- 

 rous, other nutrients, and metals were observed at dredged material removal 

 sites. 



In Cleveland Harbor (Lake Erie) only short-term adverse effects on water 

 quality were noted (U.S. Army Corps of Engineers, Buffalo District 1969c). 

 Dissolved oxygen levels in the vicinity of hopper dredging were lowered as 

 much as 25%. However, in the Rouge River at Detroit, the dredging of grossly 

 polluted sediments resulted in significant increases in the immediate area 

 of the dredge of suspended solids, volatile suspended solids, chemical and 

 biochemical oxygen demand, total phosphorous, and iron (U.S. Army Corps of 

 Engineers Buffalo District 1969d). Overflow from the hopper bins caused the 

 most severe pollution. In a test by the Corps of Engineers at a site which 

 contained very fine-grained material in Saginaw Bay (Lake Michigan), it was 

 found that half of the dredged solids washed overboard (International Working 

 Group 1975). 



Impacts to the water column (International Working Group 1975) are: (a) 

 creation of turbidity and reduction of light penetration; (b) resuspension of 

 contaminated materials in the water column; (c) dissolved oxygen depletion; 



(d) release of nutrients and other materials entrapped in the sediments; and 



(e) creation of floating scum and debris. 



Chamberlain (1976) noted that dredging for dock construction at Nanti- 

 coke, Ontario, (Lake Erie) increased turbidity which adversely impacted fishes 

 and probably restricted seasonal navigation patterns. 



Botto m Impacts 



New work dredging has a greater potential for damage to the benthos than 

 maintenance dredging (International Working Croup 1975). The change in sub- 

 strate usually permanently alters the benthic community. Additionally, pools 

 of stagnant water may be created due to "trenching" or overdredging. 



A follow-up study of channel modifications of interconnecting waterways 

 of the Great Lakes revealed that dredged navigational channels v/ere nearly 

 devoid of benthic invertebrates. Prop wash, maintenance dredging, and strong 



Due to a lack of available research specific to the Great Lakes and an incom- 

 plete survey of reference libraries, information contained in this Appendix 

 should be considered as incomplete and preliminary. Parts III and IV, Coastal 

 Waters and Rivers, should be consulted for additional information that may be 

 applicable to the Great Lakes. 



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