7796

• UCREFRP Catalog Number: 7796
• Author: Burdick, B. D.
• Title: Conceptual Management Plan for Habitat Enhancement in Flooded Bottomlands, Escalante State Wildlife Area, Gunnison River Downstream of Delta, Colorado.
• USFW Year: 1994.
• USFW - Doc Type: \
• Copyright Material: NO

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that Site 1 is used occasionally by some dabbling ducks but habitat at present
appears to be marginal for resting and nesting habitat. Ring-necked pheasant and
Gambel's quail also occur on the tract. Northern leopard frogs (Rana pipiens)
and bullfrogs (Rana catesbeiana) are present in the area. The extent of other
amphibians and reptiles on this tract is unknown. The large cottonwood forest
on the island between the two river channels to the south of the Hamilton Tract
and other cottonwood groves upstream of the tract provide roosting and resting
areas for wintering bald eagles (Haliaeetus leucocephalus). A great blue heron
(Ardea herodias) rookery is located in the cottonwood forest on the island
between the two river channels.
Generally, the input of terrestrial organic matter provides the basis for
energy in headwater streams (Vannote et al. 1980). Large rivers, such as those
of the upper basin, depend upon fine particulate organic matter from upstream
reaches for basic productivity (Vannote et al. 1980; Sedell and Richey 1989).
Although detailed ecological studies of the various habitats in the upper basin
have not been made, inferences can be drawn from the published literature. Low-
water velocity habitats are important to endangered fishes of the upper Colorado
River basin in both historical and present occupied stream reaches. A discussion
of the importance of these habitats follows.
CONCEPTUAL ECOLOGICAL MODEL
Relation of Nutrients, Sunlight Penetration, and Warm Water Temperatures
to Phytoplankton Production. Phytoplankton productivity provides the basis for
development of a food web. Phytoplankton production and standing crops increase
in concert with increases in annual input of nutrients regardless of latitude.
Carbon, nitrogen, and phosphorus are key elements for phytoplankton production.
Phosphorus is perhaps most limiting in north temperate and subarctic climates
(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
crops in north temperate freshwaters are 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 bioavailable with most of the extractable element
in the form of calcium-bound phosphorus. Therefore, Watts and Lamarra (1983)
concluded that algae production was not nutrient limited in this reach of the
Colorado River but that primary production was inversely related to the turbidity
of the riverine environment.
The rivers of the upper Colorado River basin are turbid and contain large
' expanses of sand substrate. Production of phytoplankton and zooplankton that
form the basis for a food pyramid are extremely low in these rivers (Grabowski
and Hiebert 1989; Cooper and Severn 1994 a, b, c, and d; Mabey and Shiozawa
' 1993). High turbidity obstructs the penetration of sunlight that is needed for
phytoplankton production. Backwaters and embayments along the main river
channels and flooded bottomlands in off-channel areas provide favorable
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