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|Environmental effects of Tennessee-Tombigbee Project cutoff bendways
|Environmental and Water Quality Operational Studies (U.S.)
Pennington, C. H.
Baker, John A.
|Environmental Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Abstract: Biological and physical data were collected from four bendways within the river portion of the Tennessee-Tombigbee Waterway (TTW) from Columbus, Mississippi, to Demopolis, Alabama: Rattlesnake Bend, Cooks Bend, Big Creek Bendway, and Hairston Bend. During this study, the four bendways had not all been cut off and had been impounded for various lengths of time. At the completion of the TTW project, all four of the bendways will be severed from the main navigation channel. Four distinct areas within each bendway were compared: above the bendway, within the bendway, below the bendway, and within the cut. Sampling was conducted from January 1979 to September 1980 to coincide with four different river stage/water temperature regimes. Sediment analysis and bottom profiles indicated that the substrate composition of some of the bendways is changing. Overall, the substrate of the study area is changing from a sand-gravel-fines mixture to one of predominantly sand and fines. Areas of some bendways, in particular the upper areas, were accumulating sediments. At Big Creek Bendway, this accumulation completely blocked water exchange between the river and the within-bendway areas. Few significant differences in water quality were documented for either within individual bendways or among the four bendways. Only at Big Creek Bendway were consistent differences found between within-bendway samples and river samples. Phytoplankton composition and chlorophyll concentrations showed only small differences among bendways. Aquatic macrophytes were scattered and uncommon in the four bendways. Water-willow (Justicia sp.) was most commonly encountered, particularly in Rattlesnake Bend where numerous small beds were found. Based upon total collections, a consistent family assemblage of macroinvertebrates characterized the four bendways. Although 60 family-level taxa were collected, nine families of macroinvertebrates accounted for between 93.5 and 97.2 percent of the benthos. The importance of these families varied among bendways and appeared to reflect differences in physical bendway conditions, particularly substrate type and current velocities. Eighteen species of Unionid mollusks, plus the Asian clam Corbicula, were collected during the surveys. Nearly all the specimens were found at Big Creek Bendway; none were collected at Hairston Bend. With the exception of three species of Pleurobema, no unusual or uncommon mollusk species were found. Based on overall ichthyofaunas, two groups of bendways were delineated that corresponded to impoundment and riverine habitats. Rattlesnake Bend and Cooks Bend were located in lower pool sections, where impoundment conditions prevailed, and their ichthyofaunas were dominated by clupeids (shad) and centrarchids (sunfishes, crappies, and basses). Hairston Bend, essentially a riverine reach during this study, was dominated by cyprinids (minnows) ictalurids (catfishes), and catostomids (suckers). Big Creek Bendway, unique in having both riverine and lacustrine habitats, was faunistically most similar to Hairston Bend, but also showed moderate similarities to the other bendways.
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