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|Title:||An Ecological investigation of the Baleshed Landing-Ben Lomond and Ajax Bar Dike Systems in the Lower Mississippi River Mile 481 to 494 AHP|
|Authors:||Environmental Laboratory (U.S.)|
Lower Mississippi River Environmental Program.
Baker, John A.
Kasul, Richard L. (Richard Lawrence)
Winfield, Linda E.
Bingham, C. Rex.
Pennington, C. H.
Coleman, Richard E.
Environmental impact analysis
Lower Mississippi River
|Publisher:||United States. Mississippi River Commission.|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Lower Mississippi River Environmental Program report ; 12.|
Abstract: The chemical, physical, and biological attributes of aquatic habitats associated with two Lower Mississippi River dike system pools were investigated from August 1985 to January 1986. The habitats included the dike pool at river miles (RM) 488.6 to 491.4, and the pool at RM 483.6 to 484.4. A discontinuous stretch of sandbar habitat bordering the two pools was also sampled for comparison, though at a lower level of effort. The larger pool received substantial inflow around the channel ward end of the dike, and over low points in the dike, during the entire study. Current speeds were >1.5 metres per second in most areas of the pool in all sampling periods, At comparable river stages, the upstream dike at the smaller pool was a more effective barrier to inflow. At stages below about +12 ft low water reference plane, the smaller pool isolated, and it was slack during most of August-October, and January. Even during the relatively high November river stage, current speeds in this pool were substantially lower than in the larger pool. Sand and gravel sediments were common in the larger pool in all months. In August, and to a lesser extent November, substantial areas of finer sediments were also present. In the more isolated pool, fine sediments (silt-clays) comprised the majority of the sediments until January, when sands were the dominant sediment type. Water temperature, dissolved oxygen levels, pH, and conductivity were similar in all three habitats during all sampling periods. Secchi transparency was significantly greater, and turbidity lower, in the isolated pool during August and September, but not during following months. Only in the isolated pool in September was there any indication of stratification in any water quality parameters, and the degree of stratification was slight. All water quality parameters showed seasonal variation, changing with both season and river stage. Chlorophyll a concentrations were relatively high only in September. Concentrations were similar in the two pools, while those in the river sandbar habitat were about 50 percent lower. Phaeophytin showed a peak only in November, when concentrations were similar in all habitats. No other photosynthetic pigment was found in appreciable concentration. Estimates of primary productivity showed that the isolated pool was a site of significant photosynthetic activity in August and especially September. Estimates for this habitat were still considerably lower than for a nearby abandoned channel (Lake Providence harbor), however. Values for the larger pool and for the river sandbar habitat were negative during August, and low but positive during September. The benthic macroinvertebrate assemblages found in sediment samples from the two pools were generally similar during both August and October. Oligochaetes, chironomids, ephemeropterans, and pelecypods comprised most of the numbers in August, while oligochaetes, chironomids, and trichopterans dominated in October. The dominant forms of chironomids and ephemeropterans differed, however, between the two pools. Samples of epibenthic organisms taken from the dikes in August indicated that trichopterans, and to a lesser extent ephemeropterans, were the dominant taxa. The macrobenthos of the two pools was considerably different during January. Chironomids dominated in both pools, but the major taxa were quite different. Only in the isolated pool did oligochaetes, ephemeropterans, and caddisflies remain relatively abundant. Although densities of sediment macroinvertebrates were not significantly different between the two pools in any month, densities were generally 200 to 400 percent greater in the isolated pool. No substantial differences were noted between the fish assemblages of the two pools; the fish assemblage found in the river sandbar habitat was somewhat different. Fish species composition of comparable microhabitats within the pools (dike, pool sandbar, natural bank, midpool) were also quite similar in all sampling periods. Catch per unit effort for the three gear types used showed no significant overall differences among the two pools and the river sandbar habitat. Differences among microhabitats within pools were found, however, with the pool sandbar, dike, and natural bank habitats having higher catches than the midpool. Considerable differences were noted in both species composition and catch per unit effort among months. Hydroacoustics indicated that fish were widely distributed in all microhabitats in both pools. Highest densities were generally found along the natural bank, however, and at times in the dike plunge pool. At higher river stages fish vertical distribution became more bottom- and shoreline-oriented. Target strength distributions were variable and similar in both pools.
|Appears in Collections:||USACE Collection|