Channel incision is a widespread phenomenon that results in stream and riparian habitat degradation. Fishes and physical habitat variables were

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 km 2 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 2 years before and 4 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 3 years. Accordingly, longterm 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.

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Indices o biotic integrity (IBI) were computed or two annual ish collections rom 27 locations along the blu line bordering the Mississippi River alluvial plain in northwestern Mississippi . Study sites exhibited varying degrees o physical habitat degradation due to accelerated channel erosion . Objectives o index application were to quanti y existing environmental quality and to test the IBI as a tool or relating ish population characteristics to physical degradation . Physical habitat data were collected concurrently with ish at all sites, and physical habitat descriptors were compared with the IBI scores and component metrics .Three to 23 ish species were captured rom each site, and species richness explained 64-70% o the variance in IBI scores . Fish collections were dominated by insectivores tolerant o habitat and water quality degradation . Suckers and piscivores were relatively uncommon .The IBI scores were generally not re lective o physical habitat conditions . Variation in IBI scores was indicative o only the grossest di erences in physical habitat quality . Weak relationships between physical habitat quality and IBI scores may have been due to large temporal variations in biotic integrity typical o degraded habitats . Alternatively, water quality degradation, which we did not measure, may have con ounded relationships between physical habitat and ish metrics .Regional application o the IBI as a habitat assessment tool in landscapes with widespread physical degradation must overcome lack o suitable re erence sites, large temporal variation in IBI scores, and small numbers o ish per collection, leading to lower con idence levels or IBI scores . The scarcity o lightly impacted sites may hinder detection o biotic integrity response along gradients o physical habitat quality .

The initial results are described of the restoration of 1 km long reach of Goodwin Creek, a channelized sand and gravel bed warm-water stream draining a 21 km2 lowland catchment in north-west Mississippi. Although a series of grade control weirs and bank protection works had been constructed before restoration, sediment production from channel erosion remained high (>1200 t km-'y-') and aquatic habitats were of poor value. At base flow, only 5-20% of the water area was classified as pool habitat (depth >30cm and velocity < 10 cm s-I). Restoration works were designed to be compatible with existing channel stabilization works and economic critera. Stone was added to extend the existing groynes across the base flow channel to create 18 small weirs. The effects of restoration were quantified by collecting fish and physical habitat data semi-annually for two years before and during the first year after restoration from the restored reach and from two reference streams. Restoration increased pool habitat availability, overall physical heterogeneity, riparian vegetation, shade and woody debris density. After restoration, mean width, depth and velocity exhibited changes of +56, +150 and -56%, respectively, despite discharge levels that averaged 43% lower during data collection periods. The pool area increased to 72% of the water area. Bed types became more heterogeneous, with larger fractions of clay, debris and riprap, and less sand and gravel. The fish response to restoration measures was modest, but distinct. Before restoration cyprinids and centrarchids comprised 74 and 11 %, respectively, of the numerical catch, but 32 and 55% after restoration. Fish species composition and relative abundance after restoration were slightly more similar to that of the non-incised reference site than before restoration. The median lengths of five selected fish species were greater after restoration, but were unchanged at reference sites.KEY WORDS physical habitat restoration; incised streams; stone weirs *All programs and services of the US Department of Agriculture are offered on a non-discriminatory basis without regard to race, colour, national origin, religion, sex, age, marital status or handicap.