Can Warmwater Streams Be Rehabilitated Using Watershed-Scale Standard Erosion Control Measures Alone?

Degradation of warmwater streams in agricultural landscapes is a pervasive problem, and reports of restoration effectiveness based on monitoring data are rare. Described is the outcome of rehabilitation of two deeply incised, unstable sand-and-gravel-bed streams. Channel networks of both watersheds were treated using standard erosion control measures, and aquatic habitats within 1-km-long reaches of each stream were further treated by addition of instream structures and planting woody vegetation on banks (“habitat rehabilitation”). Fish and their habitats were sampled semiannually during 1–2 years before rehabilitation, 3–4 years after rehabilitation, and 10–11 years after rehabilitation. Reaches with only erosion control measures located upstream from the habitat measure reaches and in similar streams in adjacent watersheds were sampled concurrently. Sediment concentrations declined steeply throughout both watersheds, with means ≥40% lower during the post-rehabilitation period than before. Physical effects of habitat rehabilitation were persistent through time, with pool habitat availability much higher in rehabilitated reaches than elsewhere. Fish community structure responded with major shifts in relative species abundance: as pool habitats increased after rehabilitation, small-bodied generalists and opportunists declined as certain piscivores and larger-bodied species such as centrarchids and catostomids increased. Reaches without habitat rehabilitation were significantly shallower, and fish populations there were similar to the rehabilitated reaches prior to treatment. These findings are applicable to incised, warmwater streams draining agricultural watersheds similar to those we studied. Rehabilitation of warmwater stream ecosystems is possible with current knowledge, but a major shift in stream corridor management strategies will be needed to reverse ongoing degradation trends. Apparently, conventional channel erosion controls without instream habitat measures are ineffective tools for ecosystem restoration in incised, warmwater streams of the Southeastern U.S., even if applied at the watershed scale and accompanied by significant reductions in suspended sediment concentration.