Ground and surface water in and along the broad floodplain of Willow Creek below
Creede, Colorado, are contaminated by drainage from various mine adits
and waste rock piles above the town and by leachates from a gravel-capped
tailings pile below. These waters have been sampled through a set of
18 monitoring wells and found to have elevated in metal concentrations,
especially of zinc (Zn) and cadmium (Cd). Zinc is of most concern because
of its known toxicity to freshwater fish (e.g., Beregeri and Patil, 1986;
Farag et. al., 1999; Hilmy et. al., 1987). Moreover, the mouth of Willow
Creek spills into the Rio Grande River, a prime trout fishery. At issue,
then, is the impact of the water quality of Willow Creek as it enters
the Rio Grande River. In an attempt to find a simple and cost-effective
method to monitor contamination of surface and ground water in areas
impacted by mining, we measured the content of 37 elements in willows
(sandbar willow, Salix exigua, and one blue willow, Salix drummondiana),
which grow abundantly in this study area. We collected leaf samples at 14 sites, mostly
on the Willow Creek floodplain below the town of Creede, Colorado. Willow
functions as surrogate water well and a groundwater quality sampler because
its roots usually extend into the ground water region (Robinson, 1956).
Willows have also been shown to accumulate far more Cd than do other
shrubs and trees in mineralized areas. Because Cd associates closely
with Zn in plant tissue, and willow is fairly common at the project site,
willow proved to be an ideal plant for our study.
This phytogeochemical study provided a cost-effective method
for assessing the extent of a leachate plume from generally non-point
sources. Such a method may be useful as a preliminary sampling tool to
guide the design of hydrogeochemical and geophysical studies.
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| Posted August 2005 |
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