Impacts of Copper on a Lotic Benthic Invertebrate Community: Response and Recovery

We examined the impact of copper on invertebrate community composition in a small stream (Pelican Brook) originating from a zebra mussel infested lake in central Minnesota. One bay of the lake was treated weekly with chelated copper during the summers of 2004 and 2005, resulting in copper levels in Pelican Brook ranging from 0.1 to 0.8 mg/L for three months each summer. Benthic macroinvertebrates were collected from two sites in Pelican Brook in spring and fall over four years (2004-2007), including one pretreatment collection (spring 2004). Samples were also collected from two reference streams (2005-2007). Ephemeroptera, Trichoptera, and Plecoptera comprised over half of the community in pre-treatment and reference stream samples. During treatment seasons, mayflies were eliminated and the community shifted to only a few taxa (Hydropsychidae and Chironomidae, primarily Orthocladiinae). Reference stream communities showed seasonal fluctuations but not the massive shifts in taxa abundance seen in the impacted sites. Invertebrate communities began to recover in the first year post-treatment (2006), and by fall 2007 Ephemeroptera and Trichoptera again accounted for over half of the taxa collected. Ephemeroptera, particularly Heptageniidae, appear to be good signal taxa for copper impacts.