An Ecological Investigation of Cutoff Bendways in the Tennessee-Tombigbee Waterway (Tombigbee River): An Overview

A field investigation of 3 cutoff bendways and 1 natural bendway in the Tennessee-Tombigbee Waterway (Tombigbee River) was conducted from December 1979 to September 1980. Conductivity, pH, and current were significantly different (P < 0.05) among transects regarding corresponding bendway locations. Conductivity, dissolved oxygen, current, carbon dioxide, alkalinity, secchi visibility, turbidity, ammonia, total phosphorus, and orthophosphorus were significantly different among bendways. Dissolved oxygen stratification occurred from late July through August with little or no dissolved oxygen in the bottom stratum at most transects. Six divisions of phytoplankton including 150 taxa were observed. Lowest total numbers of plankton occurred in December (l21/ml) and increased to a maximum of 20,632 organisms/ml in late August. Chlorophyll and carotenoids varied significantly with seasons and with changes in phytoplankton abundance, secchi readings, conductivity, pH, turbidity, dissolved oxygen, ammonia, and orthophosphorus. Sediment sample analysis indicated that while there were substantial amounts of gravel in 2 bendways, fme sand clearly predominated the total sediment from each transect over all bendways. The greatest number of benthic taxa was represented at the natural bendway. Transect samples from within bendways had more taxa represented and a greater density of organisms than river transect samples. Sixteen unionid mollusks were collected with representatives taken from 3 of the 4 bendways. Two species taken, Pleurobema taitianum and P. marshalli, are under status review by the Fish and Wildlife Service to determine if they are endangered Significantly (P < 0.05) higher diversities of fish were associated with stations located in bendways which had been cut off for longer time periods.

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