AN EVALUATION OF IMPACTS TO ANIMAS RIVER BENTHIC MACROINVERTEBRATE COMMUNITIES FROM THE GOLD KING MINE RELEASE

The Gold King Mine release caused a severe, but brief spike in metal concentrations in the Animas River, raising concerns about potential impacts to aquatic life. We surveyed benthic macroinvertebrate (BMI) populations along the Animas River from Silverton to Durango and analyzed potential impacts to determine whether BMI populations were impacted by the Gold King Mine release. Specifically, we investigated: 1) whether the Gold King Mine release negatively affected BMI community composition; 2) whether species known to be sensitive to metal contamination were impacted as a result of the Gold King Mine release; and 3) whether the Gold King Mine release caused a change in metal concentrations in the tissue of BMIs.

Our data suggest:

• BMI populations in the Animas River from Silverton to Durango appear to have largely survived the Gold King Mine release.

• We found no evidence that BMI families known to be sensitive to metal contamination were extirpated as a result of the Gold King Mine release.

• We found no statistically significant difference in any BMI community health metric between 2014 and 2015, indicating that the Gold King Mine release did not consistently alter BMI community structure at surveyed sites in the Animas River.

• We found that copper tissue concentrations were higher in 2015 than in 2014 at all sites affected by the Gold King Mine release.

These findings should be interpreted within the historical context of metal contamination within the Animas River watershed. BMI communities have long been stressed by long-term exposure to mine-related impacts and other factors prior to the Gold King Mine release. BMI species that are most sensitive to metal contamination (Heptageniidae, Ephemerellidae, and Taeniopterygidae) are either absent or occur at a low diversity in large portions of the Animas River, which reduces the ability to detect an impact from the Gold King Mine release. It is possible that we could have seen a greater impact to aquatic life from the Gold King Mine release in parts of the Animas River if the resident aquatic life had not already been impacted by long-term exposure to metals. Although we found no evidence of lethal impacts to aquatic life, sub-lethal impacts, such as reduced reproduction potential are possible and should be examined by assessing the survival of subsequent generations of fish and BMIs.