46 



reference stations (Section 3.3.2; Brooks 

 1983). Species abundance and numerical 

 abundance were also higher at STNH-N 

 than at the reference station, probably 

 reflecting the dramatic shift in grain size 

 from the siltier material at the reference 

 area to the predominantly sand cap. 



In addition to direct benthic sampling, 

 in 1980-81 caged mussels (Mytilus edulis) 

 were deployed on bottom-mounted racks at 

 STNH-N and STNH-S deposits, at NOR, 

 and at a reference area to monitor 

 bioaccumulation associated with solute and 

 particulate transport. Bags of mussels, 

 located approximately 1 m above the 

 sediment- water interface, were periodically 

 sampled by divers and returned to the 

 laboratory for analysis of tissue 

 concentrations of selected trace elements 

 and organic contaminants (Feng 1982). 

 Plots of the measured tissue concentrations 

 over time showed strong seasonal patterns 

 (Figure 3-6). 



The year-long caged mussel data set 

 (April 1980 - June 1981) had strong 

 temporal variability in tissue contaminant 

 concentrations. This variability was closely 

 correlated with water temperature, 

 nutritional and reproductive state, and 

 season. The highest levels were found in 

 winter when the wet/dry tissue ratios and 

 suspended sediment concentrations were 

 highest. The variations associated with 

 these factors were orders of magnitude 

 larger than any that could be assigned to 

 dredged material disposal (Feng 1982). 

 Similar results have been obtained from 

 mussel cages deployed at active dredged 

 material disposal sites in eastern Long 



Island Sound (Arimoto and Feng 1983). 

 The lack of a clear correlation between 

 contaminant body burdens and active 

 disposal supports the conclusion that any 

 "signal" of suspended contaminants due to 

 erosion from the capped mounds would be 

 lost in the general background "noise" of 

 suspended contaminants within the Sound 

 (Feng 1982). 



These results are not surprising given 

 the affinity of metal and organic 

 contaminants for sediments. Because 

 contaminants are so strongly bound to 

 sediments, it is very unlikely that the 

 suspended contaminant signal in Long 

 Island Sound would be even weakly 

 influenced by contaminants eroded from 

 the capped mound surface. If surface 

 sediments from the capped mound are 

 resuspended, the sediments in the area 

 surrounding the mound will also be 

 resuspended, and the signal will be lost in 

 the noise of the ambient sediment cloud. 

 This is particularly true when the 

 measured contaminants have been 

 integrated over long time periods by tissue 

 uptake and depuration. Although the 

 program of mussel deployments was ended 

 for these reasons, this "negative" evidence 

 is important and useful from the viewpoint 

 of environmental management because it 

 placed boundaries on the scale of possible 

 effects (SAIC 1989). 



Analyses of data sets from both the 

 benthic community and caged mussel 

 experiments showed no significant signals 

 that could be related to the presence of 

 capped mounds. The lack of a detectable 

 signal, either from water column 



Sediment Capping of Subaqueous Dredged Material Disposal Mounds 



