|Shields Jr, Fletcher|
Submitted to: River Research and Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2006
Publication Date: 9/1/2006
Citation: Shields Jr, F.D., Knight, S.S., Stofleth, J.M. 2006. Large wood addition for aquatic habitat rehabilitation in an incised, sand-bed stream, Little Topashaw Creek, Mississippi. River Research and Applications. Vol 22, Issue 7, pp 803-817. Published online 06/29/06. Interpretive Summary: Stream corridor ecosystems in agricultural watersheds are often severely degraded by erosion and sedimentation, and corrective measures involving stone are costly while cheaper ones made from felled trees (large wood) more closely resemble natural habitat features. In order to develop design criteria for large wood in deeply-eroded sand bed streams, we constructed 72 large wood structures along a stream in northern Mississippi, and we monitored fish and their habitats in treated and untreated reaches for six years. Fish communities in the treated reach became more similar to an uneroded reference stream community after construction, but large wood structures were in need or replacement or repair after only 3 years. These findings will be useful to workers seeking low-cost, natural alternatives for stream stabilization and habitat restoration.
Technical Abstract: Large wood (LW) is a key component of stream habitats, and degraded streams often contain little wood relative to less-impacted ones. Habitat rehabilitation and erosion control techniques that emphasize addition of natural wood in the form of individual elements or structures are increasingly popular. However, the efficacy of wood addition, especially in physically unstable, warmwater systems is not well established. The effects of habitat rehabilitation of Little Topashaw Creek, a sinuous, sand-bed stream draining 37 km2 in northwest Mississippi are described herein. The rehabilitation project consisted of placing 72 LW structures along eroding concave banks of a 2 km reach and planting 4000 willow cuttings in sandbars opposite or adjacent to the LW structures. Response was measured by monitoring flow, channel geometry, physical aquatic habitat, and fish populations in treated and untreated reaches for two years before and four years after rehabilitation. Initially, LW structures reduced high flow velocities at concave bank toes. Progressive failure of the LW structures and renewed erosion began during the second year after rehabilitation, with only 64% of the structures and about 10% of the willow plantings surviving for three years. Accordingly, changes in physical habitat attributable to rehabilitation were limited to an increase in LW density. Fish biomass increased in the treated reach, and species richness approximately doubled in all reaches after rehabilitation, suggesting the occurrence of some sort of stressful event prior to our study. Fish community composition shifted toward one typical of a lightly degraded reference site, but similar shifts occurred in the untreated reaches downstream, which had relatively high levels of naturally occurring LW. Large wood is a key component of sand-bed stream ecosystems, but LW addition for rehabilitation should be limited to sites with more stable beds and conditions that foster rapid woody plant colonization of sediment deposits.