|Shields Jr, Fletcher|
Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/1996
Publication Date: N/A
Interpretive Summary: Streams in many agricultural watersheds have been destabilized by historical management practices like deforestation, channelization, and a lack of on-farm conservation measures. Cost-effective strategies to restore stream channel stability and ecological resources are needed, but scientific studies of restoration projects, particularly those in unstable, warmwater streams, are scarce. Two small streams in northwest Mississippi undergoing accelerated erosion were stabilized using different structural and vegetative measures, and physical and biological response was measured for two to three years. The project which featured distribution of smaller stabilization structures along a reach produced superior and more persistent response in habitats and fish populations to the project that featured a single large structure. Vegetative measures failed due to impermeable soils and competition from an exotic vine, kudzu. These results indicate that even minor increases in pool habitat can produce desirable shifts in fish species composition and size distribution, but without a stabilization plan that specifically considers habitat restoration, improvements in biological resources will be limited and possibly not long lived. Additional research is needed to develop cost-effective approaches for establishing native woody species on banks of incised streams infested with kudzu.
Technical Abstract: Cost-effective design for incised stream habitat rehabilitation is a challenging problem, and detailed studies of outcomes are rare. Herein we present a case study of two streams (watershed size = 12 and 14 km*2) damaged by channel straightening and incision. One stream was stabilized using a metal sheet piling weir and dormant willow post planting, while the other was treated with a stone weir, stone toe bank protection, and willow sprout planting. Fishes and their physical habitats were monitored for one to two years before construction and two to three years afterward. Willow planting was not successful, so canopy, bank vegetation, and woody debris density were unchanged. Pool habitat area increased from less than 5% to more than 30% of the total aquatic area, and mean water depth at baseflow doubled in the stream with the sheet-pile weir and tripled in the stream with stone structures. Fish species richness and diversity were unchanged, but species composition shifted away from cyprinids typical of shallow, sandy runs toward pool-dwelling catostomids and centrarchids, becoming more similar to a nearby lightly-degraded reference site. Median lengths of selected centrarchids increased following rehabilitation. Physical and biological response were more persistent for the stream treated with the stone weir and bank toe protection, possibly because the stone toe produced a more uniform longitudinal distribution of cover and pool habitats than the single weir. Recovery of habitat resources in deeply incised low-order warmwater streams draining agricultural watersheds is better served by designs which feature distribution of structures along a reach rather than concentration of structure at a few points.