7799

• UCREFRP Catalog Number: 7799
• Author: Modde, T. and D. Irving.
• Title: Conceptual Management Plan for Habitat Enhancement In Old Charley Wash.
• USFW Year: 1994.
• USFW - Doc Type: \
• Copyright Material: NO

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

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

the 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 conditions for phytoplankton production. Sediments deposited in these areas where the

water velocity is decreased provide nutrients and sunlight penetrates the clearer water that allows

phytoplankton to flourish as primary producers and to stimulate production of the food chain. Low velocity

off-channel habitats become warmer than the riverine environment in the upper basin (Kaeding and

Osmundson 1988; Osmundson and Kaeding 1989). The combination of nutrients, sunlight penetration of

the water column, and warmer water temperatures in low velOCity habitats provide the best conditions for

phytoplankton production in the upper basin.

B. Importance of Low Velocity Habitats to Zooolankton Production. The importance of low velocity habitats

to the production of zooplankton for fish in riverine environments has not been documented very well. Most

riverine studies have concentrated on macroinvertebrates occurring in the drift (Waters 1969). Mabey and

Shiozawa (1993) reported that the most comprehensive studies have been made of the plankton

communities in the Orinoco River, Venezuela. Mean densitites of c1adocerans and copepods (the most

abundant taxa) were 421 organisms per liter in the Laguna la Orsinera. Welcomme (1989) summarized

zooplankton densities in floodplains in a range of 270 to 10,000 organisms per liter. Mabey and Shiozawa

(1993) documented zooplankton densities in the middle Green River as 0.3 to 1.3 organisms per liter, 1.5

to 7.1 in the Ouray backwater, 63.4 at Intersection Wash (another backwater), and 206 to 690 in Old Charlie

Wash (Woods Bottom) on the Ouray National Wildlife Refuge, located downstream from Vernal, Utah.

Grabowski and Hiebert (1989) reported 0 to 20 planktonic crustaceans (cladocerans and copepods) per liter

in the middle Green River channel and 0.02 to 17 organisms per liter in backwaters during 1987 and 1988.

In an open water habitat of the Moab Slough, immediately upstream on the Colorado River from Moab, Utah,

15