Page 806 - The Toxicology of Fishes

786 The Toxicology of Fishes

Clark Fork River

Clark Fork River
4000
Below Warm
Rock Deer Lodge Springs Ponds
3000 Creek Warm Springs Ponds
30 Butte
Brown Trout > 6 in. (Number/Mile) 1000 0 Below Deer Lodge
Km
2000

1000
800
600

400
200
0
1970 1975 1980 1985 1990 1995 2000
Year
FIGURE 19.3 Fluctuations in the abundance of brown trout (Salmo trutta) in the trout-rich, low-contamination habitat
downstream from the Warm Springs Ponds and in recontaminated habitat from near Deer Lodge. Note the difference in
scale on the y-axes.

floodplains of the Clark Fork River also presents a remediation problem of massive scope and complexity.
Natural processes will eventually replace the floodplain sediments of a meandering river, over thousands
of years. Humans could physically remove the millions of tonnes of sediments in such a floodplain, but
important questions about where to put the waste must first be resolved. It is also possible that removal
of the floodplain sediments would destabilize the river bed and could result in destroying as much or
more fish habitat as does the toxicity of sediments.

Water Contamination
Acute episodes of metal input to Clark Fork waters, accompanied by massive fish kills, once occurred
with regularity. The soils of the slickens contain high concentrations of precipitated metal salts (Nimick
and Moore, 1991). When mixed with rain water, the precipitates readily dissolve, generating acidic pools
as well as groundwater inflows and surface runoff that contain trace element concentrations thousands
of times higher than uncontaminated natural waters. Intense rainstorms in summer have washed large
amounts of this dissolved metal and acidic water into the river in the past. The river would become
acidic, red with iron mobilized from the floodplain, and enriched with extreme metal contamination
(Averett, 1961; Lipton, 1993). Throughout the 1960s and early 1970s, anecdotal reports cited dead fish
during the periods of red water and elevated metals concentrations (Peters, 1975). Eight kills were
documented between 1983 and 1992 following thunderstorms (Averrett, 1961; Johnson and Schmidt,
1988; Phillips and Lipton, 1995). Numbers of dead fish ranged from less than 20 near Rock Creek in
1959 to more than 10,000 from the Mill-Willow Bypass to Racetrack in 1984. One of the early
remediation actions in the early 1990s was construction of berms (dikes) on slickens adjacent to the
river. The berms successfully prevent overland flow of rainwater into the stream, as long as they are
maintained. Observations of discolored river water and large numbers of dead fish essentially disappeared
after the mid-1990s.