Page 813 - The Toxicology of Fishes

Mining Impacts on Fish in the Clark Fork River, Montana: A Field Ecotoxicology Case Study 793

Clark Fork
Abundance
(mean ± std. Above
individuals 0.1 m )
2
Flathead
N 100 (CF 381)
I D A H O M O N T A N A
10
1
Reference Site Flathead River 0.1

Abundance 1997 1999 Clark Turah
(mean ± std. 100 (CF 190)
individuals 0.1 m 2 )
10
100 Blackfoot River Fork
1
10
0.1
Rock Creek
Bitterroot River 100 (CF 86)
Blackfoot River
1 River Goldcreek
0.1
40 Flint Cr. 10
Rock Creek
30 1
Little Blackfoot River
20 0.1
Warm Springs Creek Galen
Exit
10 Near Galen
Anaconda 100
0 Silver Bow Creek (CF 5)
10
Butte
Baetis
1
Epeorus
Serratella
Arctopsyche
Hydropsyche
0.1
0 30 Kilometers
Map Area Baetis Serratella
Montana 0 30 Miles Hydropsyche
Epeorus
Arctopsyche
Idaho
FIGURE 19.9 Abundance of five species of insect larvae at different stations in the Clark Fork Watershed (data from
McGuire, 1999; Cain et al., 2004). Heptageniid mayfly species (Epeorus and Serratella spp.) that were found to be sensitive
in other studies (Clements, 2004) were persistently absent at the sites that were most contaminated in the Clark Fork. Of
these five species, only Hydropsyche sp. are found in Silverbow Creek.
sometimes extremely abundant. Some species from the typically absent orders of mayflies and stoneflies
progressively disappeared upstream.
The most sensitive changes in community attributes stem from species-specific differences in sensi-
tivity to metals (Clements, 2004). At a level of contamination where no change in species richness is
detectable, sensitive species can be extirpated, survivors physiologically impaired, and ecosystem func-
tions lost. In the Clark Fork watershed, for example, Silverbow Creek was always impaired, with both
lower abundances and lower numbers of species. Species richness (and other community metrics) in the
Upper Clark Fork was reduced in the Deer Lodge Valley (upper 60 km of the Clark Fork) through the
1990s but appeared to be quite similar throughout the river after that. But, some species of mayflies
(Ephemeroptera within the family Heptageniiadae) and stoneflies (Plecoptera) are absent in areas of
moderate contamination, where changes in overall species richness are not detectable (McGuire, 1999)
(Figure 19.9). The widespread abundance of Hydropsyche (Trichoptera) across the contamination gra-
dient in the Clark Fork River is also consistent with a body of literature showing that oligochaetes,
chironomids, and hydropsychid caddisflies are relatively metal tolerant.