Page 810 - The Toxicology of Fishes

790 The Toxicology of Fishes

Copper in Fine-Grained Bed Sediment

2000
Deer Lodge
1800 Gold Creek
Turah Bridge
1600
1400
Copper (mg/kg) 1200

1000
800
600
400
200
0
Jun-91 Jun-92 Jun-93 Jun-94 Jun-95 Jun-96 Jun-97 Jun-98 Jun-99 Jun-00 Jun-01 Jun-02 Jun-03
Date
FIGURE 19.6 Metal concentrations in the <63-µm fraction of sediments from three stations in the Clark Fork River,
collected nearly monthly in most years between 1991 and 2003 (Moore et al., unpublished data). Concentrations fluctuate
seasonally, at least at some stations. Concentrations at each station were generally lower from 2001 to 2003 (after
remediation) than from 1991 to 1996 (before completion of most of the remediation), but monthly data are necessary to
clearly depict the trend.

Remediation activities have extended into the upper 60 km of the Clark Fork basin, below the tailings
ponds, with the goal of reducing sediment contamination. Berms were built to reduce overland runoff,
selected areas of tailings were removed or treated in situ, and banks were stabilized in selected reaches
(Figure 19.4). Effects of remediation can be evaluated by comparing the contaminated sediments in the
period from 1991 to 1996 with the period from 2000 to 2003 (Figure 19.7). Mean concentrations of
copper at all stations were lower in the latter period, but there was great overlap among the data. The
major change was that the maximum concentrations and the minimum concentrations had both declined.
Closer analysis of a single station indicated that concentrations may have begun to increase in 2002 or
2003, raising the possibility that the effect of the initial clean-up was not being sustained (Figure 19.7).
More data are necessary before a final conclusion is possible. The Clark Fork data illustrate that the
scale of contamination in a mine-impacted river system can be massive and that small-scale variability
can be formidable. Both are important considerations for ecologists seeking “control” sites within the
river or choosing study scales for comparisons of community differences within a river.

Reservoirs
Contamination from the Butte and Anaconda mining activities occurs in the sediments of all impound-
ments along the river. In 1990, the relatively small Milltown Reservoir at the confluence of the Blackfoot
River (Figure 19.1) contained approximately 100 tonnes of cadmium, 1600 tonnes of arsenic, and 13,000
tonnes of copper. Public water wells adjacent to the reservoir were closed in the 1980s because of the
arsenic contamination. Contamination also occurs in the three reservoirs that lie between Milltown
Reservoir and Lake Pend de Oreille, at levels consistent with the downstream dilution that occurs as the
watershed progressively dilutes metals from the mining and smelting activities.

Invertebrate Exposures to Contaminants
The dose of metal that an organism experiences in a water body is determined by the bioavailability of
the metal at the scale proximate to the organism. Multiple pathways of metal exposure exist in a water