Biological and physical conditions at a newly placed gravel bar habitat in the Tombigbee River
Miller, Andrew C.; Killgore, K. Jack.; King, Robert H.; Naimo, Teresa J.
Abstract: A pool-riffle habitat was constructed in an abandoned channel of the Tombigbee River near Columbus, Miss, The habitat is located below a minimum flow release structure in Columbus Dam, which releases about 5 m³/sec surface water from Columbus Lake. The habitat was constructed with 24.000 m³ of 2- to 80-mm gravel and consists of two 60-m-long riffles separated by a short pool. The gravel constricts the river channel, increases water velocity in the riffles to 50 cm/sec, and provides substrate for aquatic organisms, The riffles are 46 m long and 24 m wide with a maximum depth of l m. After nearly 2 years in place, the substrate has not armored, and bottom material is relatively unconsolidated. Colonization by invertebrates at the gravel bar was rapid. After 3 months, 19 to 21 tax a were identified, and estimated densities were 3,496 and 2,868 individuals/m² at Riffles I and II, respectively. The fauna was dominated by oligochaetes and chironomid larvae; both groups made up about 63 percent of the community. By October 1985, approximately 8 months after placement, more than 40 macroinvertebrate taxa had been identified at the site. Total density of macroinvertebrates was estimated at 11,094 and 9,646 individuals/m² at Riffles I and II, respectively. Total biomass was 0.6610 and 0.5846 mg/m² ash free dry weight (AFDW), respectively. In October 1986, the last collection date for invertebrates, approximately 69 taxa of invertebrates were identified. Densities at Riffles I and II were estimated at 17,949 and 10,983 individuals/m², respectively. Total biomass of invertebrates was estimated at 15.5110 and 4.3290 mg AFDW/m² at Riffles I and II, respectively, Approximately 80 taxa of invertebrates have been identified at the gravel bar habitat during the 2-year study. A total of 42 species were collected in the study area, 39 were found at the gravel bar, 25 were found in the river channel, and 16 were obtained in the flume, Unusual or rare species of fishes were periodically collected at the habitat. The crystal darter, listed as endangered by the State of Mississippi, was found at the habitat, and the blue sucker, considered to be uncommon in the Tombigbee River, was found in the flume, Fish abundance was usually higher at the gravel bar than at the channel or flume. Maximum fish abundance at both the gravel bar and flume was 11.6 catch per minute (CPM) in May 1986 and 8.5 CPM at the river channel in December 1985. Shad dominated the catch at the gravel bar (43.2 percent) as well as all other sites. At the gravel bar, minnows and darters were the second most abundant group (23.8 percent), followed by sunfishes (19.8 percent) and crappie (5.5 percent). Significantly smaller sized fishes were found at the gravel bar (mean length = 94 mm) than at the flume that directs water from Columbus Lake to the river channel (mean length = 188 mm) or river channel below the habitat (mean length = 179 mm). The gravel bar is an important habitat for minnows and juvenile centrarchids while larger individuals are found in the flume and river channel. Estimated fish densities at the Columbus gravel bar (l,100 to 2,900 fishes/ha) were not as high as recorded values from natural riffles (>3,000 fishes/ha), However, lack of large instream cover (e.g. snags, undercut banks, large cobble) probably limits the population. The fish assemblage at the Columbus gravel bar is similar to that in the bendways of the Tombigbee River before completion of the waterway, However, more sport fishes were found at the Columbus site than at other bendways with similar physical conditions.
Environmental Laboratory (U.S.)
Stream ecology; Tombigbee River (Miss. and Ala.); Bars (Geomorphology); Fish habitat improvement; Molluscs