Using large restoration projects as ecological experiments: dam decommissioning and exotic fish removal in Fossil Creek Arizona

J.C. Marks, G.A. Haden, E.C. Dinger, C.D. Carter, K.A. Adams, and C.J. LeRoy. Department of Biology, Northern Arizona University, Flagstaff, AZ USA

Can we restore native food webs after decades of disturbance? How do we measure success? Fossil Creek provides a model system for assessing the ecological effects of large restoration projects. Upcoming actions include return of full flows by decommissioning a hydropower dam, and chemical removal of exotic fish creating three distinct treatments 1) a control reach above the dam with full flows and no exotics, 2) a reach where flow will be restored and exotics removed, and 3) a reach where flow will be restored but exotics will remain. Our long-term assessment program incorporates an extended "before after control impact" (BACI) design that combines surveys, stable isotope analysis and manipulative experiments. Two years of pre-restoration surveys show that the fish assemblage above the dam contains only natives whereas exotics dominate the assemblage below the dam. Stable isotopes of nitrogen indicate that the trophic level of native fish species declines below the dam, which we attribute primarily to trophic displacement by exotics. Carbon isotopes suggest increased resource overlap among macroinvertebrate functional groups in disturbed relative to pristine sites. This design will test if restoration treatments increase native species and return them to their relative positions in the "control" food web.