Consideration of year-to-year variability when determining trends in contaminated rivers
Conference
·
OSTI ID:203593
- Geological Survey, Menlo Park, CA (United States)
The upper reaches of the Clark Fork River have been heavily contaminated by mining activities since the mid-1800`s. Benthic insects have been used as bioindicators to assess trends in metal contamination along a downstream gradient in the river as remediation of the mining site occurs. In this paper, the authors demonstrate that substantial year-to-year variability of metal concentrations in these biota could confound trend detection. Two genera of caddisflies (Hydropsyche sp. and Arctopsyche sp.) and one genus of stonefly (Claassenia sp.) were collected over a 400 km study area every August between 1986 and 1994. Mean metal concentrations differed up to fourfold between years, due at least in part to variability in physical or chemical processes, Total yearly discharge in the Clark Fork River continually declined during the 1986 (highest cumulative discharge) to 1992 (lowest cumulative discharge) period. In 1993 discharge levels increased to near 1986 levels. Significant positive correlations were found between metal concentrations in insects and discharge. During the highest flow year, in 1986, the highest concentrations of Cu, Cd, Fe and Pb were found in the biota. Low flow conditions in 1992 resulted in the lowest concentrations of these metals, but concentrations returned to high levels in 1993. The strongest correlation with flows were found in the upper reach, where contamination was the most severe and the sources were most immediate.
- OSTI ID:
- 203593
- Report Number(s):
- CONF-9511137--; ISBN 1-880611-03-1
- Country of Publication:
- United States
- Language:
- English
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