9371

• UCREFRP Catalog Number: 9371
• Author: Levee Removal Evaluation Group.
• Title: Green River levee Removal and Floodplain Connectivity Evaluation.
• USFW Year: 1998.
• USFW - Doc Type: CAP-6 LR,
• Copyright Material: NO

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BACKGROUND
Floodplains have an influential role on river ecology (Bayley 1995, Ligon et al. 1995,
Townsend 1996). The annual hydrologic cycle of a floodplain consists of a periodic cycle of
inundation and recession, typically associated with seasonal weather patterns. River ecosystem
productivity has been shown to be limited by floodplain availability in some instances (Newbold
et al. 1983, Tiessen et al. 1994). In large river systems, significant available portions of nitrogen
and phosphorous are derived from floodplain habitats. They influence food web productivity
through the input of limiting nutrients from the bottom up in a hierarchical manner (Newbold et
al. 1983, Vought et al. 1994, Leonardson et al. 1994). Nutrients in solution, derived from
floodplain detritus and soils, are available for autochthonous production (photosynthesis) in the
growth of phytoplankton and periphyton. This process initiates the assimilation of floodplain
nutrients and potential productivity into aquatic food webs. Invertebrates play an influential role
in continuing the assimilation of potential productivity into aquatic food webs. Aquatic
invertebrates feed on periphyton, phytoplankton, and detritus, incorporating nutrients and
biomass derived from the floodplain into the riverine food web. Grazer, shredder, and filter
feeding invertebrates are in turn eaten by predatory invertebrates and fish, thus assimilating
floodplain productivity into the top levels of the food web.
Zooplankton and aquatic invertebrate larvae are an important food resource to juvenile
fish. Therefore, the high density and diversity of invertebrate assemblages within floodplain
habitats represents an augmented food resource to juvenile endangered fish. Because of
enhanced productivity of food organisms, floodplain wetlands facilitate rapid fish growth and
survival (Osmundson 1986) and enhance fish survivorship within the river system. Native
young-of-year (YOY) fish that leave the river and use floodplain wetlands should grow faster
i than if they had remained in the river. Larger native (YOY) fish should be less susceptible to
predation by most nonnative fish in the main channel. Thus, it is hypothesized that floodplain
restoration will provide juvenile endangered fish access to high quality nursery habitat with
' enhanced food resources and favorable physical conditions which should enhance survivorship.
These potential benefits could be offset, however, if large numbers of nonnative fish species also
use these habitats.
Floodplain habitats in the middle Green River are believed to be important to razorback
sucker and other native fishes (Wydoski and Wick 1998, Modde 1997). The chronology of
spawning and larval emergence (Tyus and Karp 1990, Modde et al. 1996, Muth 1998), as well
as a linkage between juvenile razorback sucker and floodplains (Modde 1996) has led some to
suggest that floodplain habitats are important to early life stages of razorback sucker. In
' response to an increasing body of data linking floodplain habitat to razorback sucker, the
Recovery Implementation Program (RIP) initiated a floodplain enhancement program which
includes floodplain acquisition (David Soker, U.S. Fish and Wildlife Service, personal
communication) and construction (e.g., levee removal) to increase access of floodplains to m
endangered fishes. The goal of this program is to enhance floodplain habitats for the benefit of
endangered fishes.
1 However, several issues have arisen that address the biological costs and benefits of :
floodplain enhancement. Lentsch et al. (1996) presented a levee removal strategy that outlined
the need to monitor natural as well as enhanced floodplain habitats and emphasized yt1le need M
monitor the impact of floodplain enhancement on the status of nonnative fishes in tti@'Gree&
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