INTEGRATED LABORATORY AND FIELD APPROACH FOR ASSESSING IMPACTS OF HEAVY-METALS AT THE ARKANSAS RIVER, COLORADO

This research employed an integrated laboratory and field approach lo assess effects of heavy metals at the Arkansas River, a Colorado strea m impacted by historic mining operations. Ambient metal levels, chroni c toxicity, metal bioaccumulation by benthic organisms, and benthic co mmunity structure were examined at stations located upstream and downs tream from California Gulch (CG), a U.S. Environmental Protection Agen cy Superfund site near Leadville, Colorado. Although each approach dem onstrated effects of metals from CG, important differences among appro aches were observed. Ambient metal concentrations and chronic toxicity tests conducted with Ceriodaphnia dubia indicated reduced water quali ty at upstream and downstream stations. Because of temporal variabilit y in metal levels, water samples collected for chronic toxicity tests did not reflect average exposure conditions. Instream monitoring of be nthic communities was necessary to characterize metal impacts at the A rkansas River, but this approach had limitations. Levels of metals in periphyton and benthic invertebrates were significantly elevated at st ations downstream from CG. Variation in metal levels among taxa and th e absence of some taxa from some stations may limit the use of bioaccu mulation studies for monitoring metal impacts. Benthic community struc ture was altered downstream from CG, but some metrics (e.g., species r ichness, abundance) were not affected by heavy metals because of the r eplacement of sensitive taxa by tolerant taxa. Because each of the app roaches employed in this study provided different information on the d egree of metal impacts, we recommend an integrated approach for assess ing effects of metals on streams.