9389

• UCREFRP Catalog Number: 9389
• Author: Birchell, G. J., K. Chrisopherson, C. Crosby, T. Crowl, J. Gourley, M. Townsend, S. Goeking, T. Modde, M. Fuller and P. Nelson.
• Title: The Levee Removal Project
• USFW Year: 2002.
• USFW - Doc Type: Assessment of Floodplain Habitat Restoration in the Middle Green River.
• Copyright Material: NO

production can be attributed to the lateral exchange of allochthonous material and
nutrients between the floodplain and the main river channel during the annual flood
pulse. The flood pulse creates access to a variety of ephemeral habitats such as
backwaters, marshes, and lateral ponds. Areas of inundation are colonized by aquatic
biota with life histories synchronized with annual access to these favorable habitats with
high resource availability. The recession of flood waters transports nutrients, detritus,
and organisms back into the main river channel (Johnson et al. 1995). Many studies
provide additional evidence supporting this concept (Gosselink and Tumer 1978, Odum
1984, Ward 1989), especially in large, tropical riverine systems.
The River Continuum Concept (Vannote et al. 1980) states that rivers are
dependent on longitudinal linkages that transfer energy downstream. A significant
portion of this energy is composed of allochthonous input in the form of terrestrial
vegetation detritus derived from upper reach riparian and floodplain habitats. A
combination of the two concepts would argue that the input of allochthonous detritus
derived from riparian and floodplain habitats during floods is a significant source of
energy input to these ecosystems (Vannote et al. 1980, Junk et al. 1989, Johnson et al.
1995), not only for the immediate adjacent riverine system but also for downstream
reaches.
Ward and Stanford (1995) expanded on the River Continuum Concept with the
development of the Serial Discontinuity Concept which theorizes that dams interrupt the
longitudinal energy flow in river systems. Reservoirs behind dams serve to trap coarse
and fine particulate organic matter and interrupt sediment transport, both important to
longitudinal energy transfer. The rivers below these energy transfer interruptions are
then dependent on light or the lateral exchange of allochthonous input from floodplains
for energy input. The Green River below Flaming Gorge Dam is set in a similar scenario
of inten'upted energy flow and dependence on lateral exchanges with the floodplain for
energy input.
These lateral exchanges enhance biological productivity and maintain a diverse
and rich assemblage of species (Bayley 1995). Mesic conditions promote the
development of riparian vegetation characterized by a highly productive plant
community. Many invertebrates have evolved life history strategies that take advantage
of increased habitat availability and food resources associated with the inundation of
floodplain and riparian habitats (Junk et al. 1989, Goulding 1980). An invertebrate
assemblage characterized by increased density and species diversity develops in
association with cyclic floodplain inundation (Sparks 1995, Bayley 1995, Allan and
Flecker 1993).
River ecosystem productivity has been shown to be limited by nitrogen and
phosphorous availability in some instances (Newbold et al. 1983, Tiessen et at. 1994).
In large river systems, significant available portions of the these nutrients are derived
from floodplain habitats. Floodplains 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.
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