Conducting the Environmental Impact Analysis and Assessment - Environmental Impact Analysis: Process and Methods - page 209

7.00%

6.00%

No sediment cover

1 mm sediment cover

5.00%

3 mm sediment cover

4.00%

3.00%

2.00%

1.00%

0.00%

Limestone Taconite Coal Native sediment

FIGURE 5.16
Percent attachment by immature (veliger) mussels to DCR with 1 mm and 3 mm sediment
cover compared with native sediments.

r Veligers prefer to attach to DCR and thus the presence of DCR could
potentially result in the spreading and increased density of invasive
mussels in the Great Lakes. However, the probability of this occur-
ring is greatly reduced by two factors: the in situ covering of DCR
which naturally occurs greatly decreases the likelihood of veliger
attachment and in areas which already support a high density of
mussels, the old shells and live mussels provide ample opportu-
nity of veliger attachment and addition of DCR will make very little
difference.
r Lakes Erie and Ontario currently support wide zebra and quagga
mussel distribution and dense populations. Thus there is sufficient
suitable attachment substrate present and the addition of DCR in
these lakes will not produce any adverse impact from invasive
mussels.
r The open waters of Lake Superior do not currently support invasive
mussel populations and the literature documents that their absence
is due not to a scarcity of suitable attachment substrate, but rather to
water softness (i.e., low concentrations of minerals including calcium)
and the addition of DCR will not alter the softness of the water as the
mussel population's limiting factor. Thus there would be no effect on