Effects of multiple stressors on hyporheic invertebrates in a lotic system

The impacts of co-occurring stressors (river regulation by a dam and mine drainage) on hyporheic macroinvertebrate assemblages and environmental variables were investigated in a mountainous area of central Colorado at seven sampling sites in Lake Fork during two different seasons. Specific aquatic macroinvertebrate assemblages were associated with river regulation and trace element impacts. Paraleuctra was primarily associated with mining impacted sites, while Polycelis, Hydra, and Simulium were most abundant at sites nearest the dam. There were sometimes large differences in toxicity between hyporheic and surface water samples. Occasionally toxicity was present in the surface water, but absent in hyporheic water from the same site, while on one date, toxicity was detected in the hyporheic but undetected in surface water. The distinct taxa found in the hyporheic, and differences between hyporheic and surface water quality suggest that understanding the hyporheic zone is important in the study of impacted aquatic systems.