9410

• UCREFRP Catalog Number: 9410
• Author: Wydoski, R. S. and E. J. Wick.
• Title: Ecological Value of Floodplain Habitats to Razorback Suckers in the Upper Colorado River Basin.
• USFW Year: 1998.
• USFW - Doc Type: Denver.
• Copyright Material: NO

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classification systems for wetlands and surface waters yet these wetlands are
extremely important habitats for plants and animals that are adapted to the
sporatic availability of water (National Research Council 1992).

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Welcomme (1995) and Ward and Stanford (1995) emphasized that the diversity,
resilience, and integrity of large river ecosystems are related to the
connectivity of the main channel and its associated floodplain. However,
there is an increasing trend in regulating streamflows of large river systems
to increase productivity of basins for agriculture and make them safer for
human occupation. Generally, such modification of aquatic environments
adversely affects the fish stocks in large river systems. Welcomme (1985)
stated that the majority of riverine fish species are extremely sensitive to
modifications in the flood cycle and other environmental alterations caused by
regulated streamflows. Welcomme emphasized that substantial shifts in
composition of the fish community result from introduction of nonnative
species that poses uncertainty of restoring native fish assemblages by simple
natural processes. Therefore, river management planning must include
floodplains that are essential to maintaining the productivity and integrity
of large river systems.

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A. Relation of Nutrients. Sunliqht Penetration. and Warm Water Temperatures
to Primary Production. Primary production is the basis for development of
a food web through phytoplankton and periphyhton standing crops that
increase in concert with higher inputs of nutrients regardless of
latitude. Carbon, nitrogen, and phosphorus are key elements for
phytoplankton production. Phosphorus is the most limiting element in
north temperate and subarctic waters (Schindler 1978). Nitrogen is the
most abundant element in the atmosphere and is generally not limiting.
Also, abundant carbon dioxide in the atmosphere provides the necessary
carbon. Therefore, phytoplankton production and standing crop in north
temperate freshwaters is generally proportional to the phosphorus input.
Particulate phosphorus, either chemically desorbed or actively mobilized
by microbiota, is not readily available in rivers with a high sediment
load because most of the phosphorus is bound to the sediments (Ellis and
Stanford 1988). Watts and Lamarra (1983) determined that between 21~ and
49~ of the total phosphorus in Colorado River water at the bridge upstream
from Moab, Utah in September and October 1978 was available as an
extractable form of calcium-bound phosphorus and they concluded that algae
production was inversely related to river turbidity.

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Turbidity from suspended fine sediments in Upper Colorado River Basin
rivers is high and affects primary and secondary production. Production
of phytoplankton and zooplankton that form the basis for a food pyramid
are extremely low in the these rivers (Grabowski and Hiebert 1989; Cooper
and Severn 1994 a, b, c, and d; Mabey and Shiozawa 1993). High turbidity
in the river channel obstructs the penetration of sunlight that is needed
for phytoplankton production. However, backwaters and embayments along
the main river channels and marshes, wetlands, ponds, and lakes in
floodplains provide favorable conditions for phytoplankton production.
Sediments that are deposited in low water velocity areas provide nutrients
and sunlight penetrates the clearer water allowing phytoplankton and
periphyton to flourish as primary producers and to stimulate development
of the food chain. Low velocity off-channel habitats also become warmer
than the riverine environment in the Upper Basin that also aids
phytoplankton production (Kaeding and Osmundson 1988). The combination of
nutrients, sunlight penetration of the water column, and warmer water
temperatures in low velocity off-channel habitats provide the best
conditions for phytoplankton and zooplankton production in the Upper
Basin.

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B. Imoortance of Floodolain Habitats to Secondary Production. Low velocity
habitats are also important to secondary production of zooplankton in

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