Rehabilitation of aquatic habitats in warmwater streams damaged by channelincision in Mississippi

Channel incision has major impacts on stream corridor ecosystems, leading t o reduced spatial habitat heterogeneity, greater temporal instability, less stream-floodplain interaction, and shifts in fish community structure. Mos t literature dealing with channel incision examines physical processes and erosion control. A study of incised warmwater stream rehabilitation was con ducted to develop and demonstrate techniques that would be economically fea sible for integration with more orthodox, extensively employed watershed st abilization techniques (e.g., structural bank protection, grade control str uctures, small reservoirs, and land treatment). One-km reaches of each of f ive northwest Mississippi streams with contributing drainage areas between 16 and 205 km(2) were selected for a 5-year study. During the study two rea ches were modified by adding woody vegetation and stone structure to rehabi litate habitats degraded by erosion and channelization. The other three rea ches provided reference data, as two of them were degraded but not rehabili tated, and the third was only lightly degraded. Rehabilitation approaches w ere guided by conceptual models of incised channel evolution and fish commu nity structure in small warmwater streams. These models indicated that reha bilitation efforts should focus on aggradational reaches in the downstream portions of incising watersheds, and that ecological status could be improv ed by inducing formation and maintenance of stable pool habitats. Fish and physical habitat attributes were sampled from each stream during t he Spring and Fall for 5 years, and thalweg and cross-section surveys were performed twice during the same period. Rehabilitation increased pool habit at availability, and made the treated sites physically more similar to the lightly degraded reference site. Fish communities generally responded as su ggested by the aforementioned conceptual model of fish community structure. Species composition shifted away from small colonists (principally cyprini ds and small centrarchids) toward larger centrarchids, catostomids, and ict alurids. Fish density and species richness increased at one rehabilitated s ite but remained stable at the other, suggesting that the sites occupied di fferent initial states and endpoints within the conceptual model, and diffe red in their accessibility to sources of colonizing organisms. These experi ments suggest that major gains in stream ecosystem rehabilitation can be ma de through relatively modest but well-designed efforts to modify degraded p hysical habitats.