Due to the dynamic nature of rivers, chances in bottotr topography are 

 characteristic and frequent (Sir^ons et al. 197^, 1975) and rriost organisms 

 quickly adjust to perturbations (Johnson 1P76). However, dredged material, 

 placed in certain slackwater areas, such as near or on wing and closing dams, 

 can change an irregular bottom to a sandy, smooth, and shallow bottom. The 

 latter habitat is less productive of benthic organisms and offers much poorer 

 habitat for fish than a deeper, rouoher bottom (U.S. Army Corps of Engineers, 

 St. Paul District 1974, Grunwald 1976). 



Information is lacking about the burial of organisms by river dredging. 

 Kussels are of primary concern in freshwater. The Corps of Engineers, St. Paul 

 District (1974) reported that 10 yr may be required for recolonization by 

 mussels. Rogers (1976) reported a low survival rate of clams ( Sphacrium trans- 

 versum and S_^ s triatinum ) buried with sand. Survival was somewhat better with 

 the addition cf silt or silt-sand mixture. Adult clam survival was inversely 

 related to both particle size and depth of added substrate. Juvenile clams 

 had higher survival rates than adults. 



Marking and Bills (in press) studied the ability of three mussels -- 

 pig-toe ( Fusconaia flava), fat mucket ( Lampsili s radia ta lu teola ), and pocket- 

 book (L_^ ventricosal ~- to emerge from 5 to 25 cm (2~to 10 in) coverage of 

 sand and silt. The mussels emerged within a few hours or did not emerge at 

 all. Those that did not emerge eventually died. The studies showed that the 

 type of soil overlay made little difference in the emergence of fat mucket and 

 pocketbook mussels but did affect the emergence of the smaller pig-toes. The 

 emergence of the latter two species was prevented by 18 cm (7 in) or more of 

 sand or silt but only 10 cm (4 in) of silt was sufficient to kill the pig-toe. 

 The authors concluded that the ability of mussels to emerge from soil cover is 

 related to species and size. Changes in substrate composition and bottom topo- 

 graphy can alter the benthic fauna and affect fish use and concentrations. 



In the Columbia River, Washington and Oregon, a decline in fish catch and 

 species variety was noted at both dredging and disposal areas 40 days after 

 dredging. However, at sites that were only slightly disturbed by dredging, 

 there was an increase in catch (U.S. Army Corps of Engineers, Portland Dis- 

 trict 1975). 



Dispersion and release of noxious material is a concern whenever a con- 

 taminated channel is dredged, but little is known of the actual impacts. The 

 general contaminant level is probably less in rivers than in estuaries where 

 harbors may be highly polluted. However, because the buffering capacity of 

 salts is less in fresh water, there is a great potential in rivers for detri- 

 mental impacts from some contaminants such as heavy metals. 



Dredged material from rivers may contain the following potential contam- 

 inants and biostimulants: hydrogen sulfide, methane, organic acids, orthophos- 

 phates, nitroaen in several forms includinq ammonia, oils and greases, pesti- 

 cides, PCBs, "and heavy metals. High levels of PCEs, oils, DDT, and dieldrin 

 were found in harbor sediments of the Mississippi River at Mem-phis (Fulk et 

 al. 1975). Settling tests indicated that these materials became suspended in 

 the water column during agitation but under quiescent conditions concentra- 

 tions returned to near background water column levels within 14 hr. Our 

 conclusion from the study, wh'ich also included other freshwater sites is that 

 river currents will carry suspended toxic materials for some distance before 

 they settle out in quiet waters. 



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