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<br />Introduction <br />Little is known of how microcrustacean communities may have been influenced <br />by natural flood regimes since most major rivers have been dammed for flood control <br />and the production of electric power. Most work on riverine microcrustaceans has <br />concentrated on organisms occurring as plankton or drift in the rheic environment <br />(Sandlund 1982, Rossaro 1988, Saunders and Lewis 1988a, 1988b; Bothar and Kiss <br />1990, Robertson 1990). These studies seldom address the source of the organisms, <br />which are usually assumed to reproduce in slow or still water habitats. Areas such as <br />river channel backwaters, floodplains, marshes, oxbows, natural lakes, reservoirs, <br />pools, and side channels are typically considered to be reproduction sites (Clifford <br />1972, Saunders and Lewis 1988a, Saunders and Lewis 1989). The most comprehensive <br />studies of the planktonic association between rivers and floodplains are those of <br />Saunders and Lewis (1988a, 1988b, 1989) and Twombly and Lewis (1987, 1989) on <br />the Orinoco River, Venezuela and its tributaries. Their studies have focused on <br />planktonic species and they have assessed the role of the floodplain as a source area. <br />They did not examine the benthos but others, sampling streams, have shown that <br />significant numbers of microcrustaceans can occur in the lotic benthos and hyporheos <br />(Shiozawa 1986, Richardson 1991, Shiozawa 1991). <br />No studies of the relative roles of different benthic environments in riverine <br />systems has been made, yet collectively, these studies indicate that a tight integration <br />between the river and both the benthos and the quiet water habitats should exist. <br />This study was undertaken to quantify and compare the densities of benthic <br />2 <br />