Evaluation of
Exposure-Effects Relationships of Metals in the Benthic Macroinvertebrate
Community in the Upper Clark Fork River, Montana.
Naddy RB, Gensemer
RW, Vertucci FA, Stubblefield WA.
ENSR, 4303 W. La Porte Ave.,
Fort Collins, CO 80521
Abstract. Previously published
studies conducted on the Upper Clark Fork River (UCFR) suggest adverse effects
due to metals-enriched sediments found in the depositional areas that comprise
approximately 4% of the riverbed. While
these studies measure exposure concentrations from depositional areas, effects
measurements (e.g., benthic invertebrate abundance and diversity measures and
tissue residues) have been predominantly obtained from coarse substrate riffle
areas. Comparing exposure data from
one habitat to effects data from another is problematic. An integrated approach was conducted to assess effects data
by sampling benthic macroinvertebrates for community composition measurements,
tissue residues, and sediment contaminant concentrations.
Thirteen co-located sampling sites along the UCFR were sampled in both
depositional and riffle habitats in 1996. Metals concentrations in bulk
sediments and benthic invertebrate tissues decreased with distance from metals
sources in the headwaters, but sediment porewater concentrations did not.
Although there were some significant relationships between bulk sediment metals
concentrations and tissue metals residues, BMI community metrics did not appear
to vary along this gradient, or with exposure concentrations.
This is consistent with an evaluation of sediment toxicity tests
performed using sediments from Warm Springs Ponds, as well as the UCFR, which do
not suggest that metals are of potential concern to benthic macroinvertebrates.