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<br />Introduction <br /> <br />Inundated floodplains and terraces, hereafter referred to as floodplain wetlands, constitute a <br />highly productive component of the riverine ecosystem. In the Colorado River system. floodplain <br />wetlands consist of shallow, slow-moving water typically with higher nutrient concentrations, <br />primary productivity and invertebrate densities than adjacent areas of main channel flow (ongoing <br />studies by Shiozawa; Cooper and Severn 1994 a, b, c, and d; e.g. Forsberg et al. 1993). Thesc <br />wetlands may serve as essential rearing and feeding areas for some native fish species, including <br />the endangered razorback sucker (Xyrauehen lexanus) and Colorado squawfish (Ptyehoeheilus <br />lueius). The Upper Colorado River Basin Recovery Implementation Program (UCRBRIP) has <br />targeted acquisition and reinstitution of active floodplain wetlands (within the 100-year <br />floodplain) to main channel flows as a priority recovery activity. However, effective management <br />of thcse wetlands for recovery of endangered fish requires considerable understanding of <br />Colorado River wetland ecology. The necessary information will be acquired through research <br />and experimentation which is implemented on a graduated temporal and spatial scale. This <br />schedule allows evaluation of preliminary efforts and subsequent modification to prevent <br />prodigious effort and expense at the onset of the project. <br /> <br />Baek'{l'ollnd <br /> <br />Previous research documented the importance of main channel low velocity areas (e.g., <br />backwaters) as native fish habitat (Tyus and Karp 1991). More recent research focused on the <br />geomorphology of nursery habitats (pucherelli et a1. 1990; Rakowski and Schmidt 1995) and their <br />ecological function in Colorado squawfish and razorback sucker population dynamics (UDWR <br />and USFWS ongoing projects). Floodplain wetlands may be equally important as biologicaliy <br />complex habitat for endangered tish. Furthermore, a reduction of channel and floodplain <br />complexity associated with dam construction, flood control and riparian vegetational changes <br />over the last 100 years (Andrews 1986) lcnds urgency to understanding and restoring a functional, <br />integrated floodplain system in the Upper Colorado River system. <br /> <br />Floodplain wetlands generally are areas of high primary productivity due to elevated water <br />temperatures, nutrient levels, and light intensities. Decaying plant material (emergent and flooded <br />terrestrial vegetation) supports a large portion of the decompositional pathway within the riverine <br />food web. Consequently, macroinvertebrate production is high because of an enriched food base <br />(phytoplankton, etc.), a structurally complex environment (structure provided by emergent plants, <br />flooded vegetation, and algal mats), and relatively warm water temperatures. These factors taken <br />in aggregate suggest that floodplain wetlands are extremely productive habitats. <br /> <br />Because of enhanced productivity of food organisms, floodplain wetlands facilitate rapid fish <br />growth within the floodplain and survival within the main channel (Osmundson and Kaeding <br />1989). Growth of native young-of-the-year (yay) fish in floodplain wetlands is enhanced <br />because of greater food abundance and higher growth rates; subsequently, survivorship of yay <br /> <br />4 <br />