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Title: Water quality, macroinvertebrates, larval fishes, and fishes of the lower Mississippi River--a synthesis
Authors: Environmental and Water Quality Operational Studies (U.S.)
Beckett, David C.
Pennington, C. H.
Keywords: Mississippi River
Benthic macroinvertebrates
Water quality
Larval fishes
Dike fields
Stream ecology
Publisher: Environmental Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Technical Report
Abstract: This is a synoptic report describing water quality and composition and distribution of benthic macroinvertebrates, larval fishes, and fishes within a 62-mile reach of the lower Mississippi River. Major water quality differences among habitats were related to the presence or absence of current. Continual flow and high turbulence in !otic habitats such as the main channel and permanent secondary channel resulted in high suspended solids concentrations, high turbidities, low water transparencies, and low light penetration. Such physical characteristics resulted in low algal biomass, more stable pH and dissolved oxygen levels, and the constant availability of algal nutrients. In contrast, lentic areas, such as the abandoned channel at most river stages, and the dike fields at low flows, had relatively lower suspended solids and increased water clarity. This resulted in high algal biomass, higher pH readings, frequent dissolved oxygen supersaturation in surface waters, and nutrient depletion in slack-water areas. The distribution of macroinvertebrates in the lower Mississippi River is a function of the physical characteristics of the system, notably current velocity and substrate composition. Natural banks were consistently dominated by the clay-burrowing mayflies Tortopus incertus and Pentagenia vittigera, and hydropsychid caddisflies; the consistently most common taxa in the permanently flowing secondary channel were the sand-dwelling chironomids Robackia claviger and Chernovskiia orbicus; phantom midges, tubificid oligochaetes, and fingernail clams were always the most abundant macroinvertebrates in the slack-water abandoned channel. However, the dike fields showed large changes in biotic composition over different flow regimes. These biotic changes corresponded with alterations in current and substrate. The rock dike structures were densely colonized by epibenthic organisms. Three principal factors determine ichthyoplankton composition and distribution: larval phenology, habitat characteristics, and river stage. The progeny of early spawners such as gizzard shad, mooneye, goldeye, carp, buffaloes, and sauger dominated spring and early summer ichthyoplankton collections, while freshwater drum, carpsuckers, and Lepomis spp. dominated the mid to late summer ichthyoplankton community. Ichthyoplankton composition in the backwaters (shad, Lepomis spp., and silversides) was markedly dissimilar from that of the main channel (drum and carpsuckers). Isolated dike field pools were populated by larval fishes typical of backwater habitats. In general, backwater and slack-water habitats supported much higher ichthyoplankton densities than lotic areas. The lower Mississippi River possesses a number of fish species which are restricted to (bullheads, bowfin, and spotted gar) or prefer backwater areas (bluegill, largemouth bass, white and black crappies, paddlefish, and alligator gar). Swift current areas of the lower Mississippi support shovelnose sturgeon (fairly common), blue sucker (fairly common), and blue catfish (abundant) populations; these three species have all suffered major declines in abundance in the impounded upper Mississippi. Dike fields have diverse fish faunas. This diversity is a product of physical structure and the varying of physical conditions within the dike fields with changing river stages. The dike fields' middle bars furnish large shallow "shoreline" areas which are populated by a diverse and abundant community of small fish species and young-of-the-year fishes or larger species. These studies have shown that the abandoned channel and dike field pool habitats are of special concern and importance. The placement of dikes and revetments along the river has prevented channel meandering by "locking" the river into a permanent alignment. Consequently, abandoned channels are rarely created now. Existing abandoned channels should therefore be protected from filling in or being dewatered. The formation of lake-like pools in the dike fields during low flow is precluded by the filling in of these areas. Engineering practices which would prevent or delay the "terrestrialization" of dike fields should be encouraged in the lower Mississippi River.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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