7904

• UCREFRP Catalog Number: 7904
• Author: Lentsch, L. D., T. Crowl, P. Nelson and T. Modde.
• Title: Levee Removal Strategic Plan - Final Report.
• USFW Year: 1996.
• USFW - Doc Type: Salt Lake City, UT.
• Copyright Material: NO

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