|Shields Jr, Fletcher|
Submitted to: Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2006
Publication Date: 7/1/2007
Citation: Shields Jr, F.D., Knight, S.S., Cooper, C.M. 2007. Can warmwater streams be rehabilitated using watershed-scale standard erosion control measures alone? Environmental Management 40:62-79. DOI 10.1007/s00267-006-0191-0. Interpretive Summary: Stream corridor ecosystems in agricultural landscapes are often badly degraded, and scientists disagree about the best approaches for restoration. One-km long sections of two streams with rapidly eroding watersheds were modified to improve fish habitats and monitored for 10 years, along with upstream sections of the same and adjacent streams that were modified using only standard erosion control practices. Habitat modifications produced major shifts in the types and sizes of fish that did not occur in the other stream sections. These findings will be useful to scientists, engineers, and land managers working in the area of stream ecosystem restoration.
Technical Abstract: Degradation of aquatic habitats, especially warmwater streams in agricultural landscapes is a pervasive problem. Although projects to rehabilitate stream ecosystems have become quite numerous, reports of effectiveness based on monitoring data are rare. Some workers suggest that rehabilitation efforts are more likely to be successful if they are extensively applied across entire watersheds, with reduced emphasis on reach-scale instream or riparian measures. Described is the outcome of rehabilitation of two deeply incised, unstable warmwater streams. Channel networks of both watersheds had been treated using standard erosion control measures. Aquatic habitats within 1-km long reaches of each stream were further treated by addition of stone instream structures and planting woody vegetation. Fish and data describing their habitats were sampled at base flow for 1-2 years before treatment and 11 years after treatment. Unrehabilitated reaches upstream and in similar streams in adjacent watersheds were sampled concurrently. Physical effects of treatments were persistent through time, with pool habitat availability much higher in treated reaches than elsewhere. Fish community structure responded with major shifts in relative species abundance: as pool habitats increased following rehabilitation, small-bodied generalists and opportunists declined as larger-bodied predators such as centrarchids and catostomids increased. In general, rehabilitated reaches supported fewer but larger fish and more species of fish. Reaches immediately upstream from rehabilitated reaches experienced the same hydrology and water quality but were significantly shallower, and fish populations there were similar to the rehabilitated reaches prior to treatment. Conservation and restoration 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. At least over the time scale of a decade, conventional channel erosion controls without instream habitat measures are ineffective tools for ecosystem restoration in incised, warmwater streams of the Southeastern U.S. General prediction regarding restoration outcomes is difficult because physical and ecological responses of a given stream ecosystem to rehabilitation will reflect site-specific factors.