7068

• UCREFRP Catalog Number: 7068
• Author: Bishop, B. A. and D. B. Porcella.
• Title: Physical and Ecological Aspects of the Upper Colorado River Basin.
• USFW Year: 1980.
• USFW - Doc Type: 17-55
• Copyright Material: YES

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Water quality problems in specific locales include: acid mine

drainage and heavy metal pollution in tributaries of the west slope of

the Rockies, energy impacts on water quality, reservoir eutrophication

and sedimentation, biochemical oxygen demand (BOD) and dissolved oxygen

(DO) interactions below treatment facilities, and potential health prob-

lems associated with the discharge of municipal sewage. These impacts

may interfere with rare and endangered floral and faunal species, and

recreational pursuits.
At present, from the standpoint of the entire basin, the most criti-

cal water quality problem of the Colorado River is the salinity or total

dissolved solids (TDS) content of the water. It is also the problem

which is most affected by the natural background conditions of the basin.

Comparisons of salt loading and salinity concentrations at various points

on the river system have been estimated in a number of different studies

(Irons and coauthors, 1965; Hyatt and coauthors, 1970; Colorado River
Board of California, 1970; U.S. Environmental Protection Agency, 1971;
U.S. Water Resources Council, 1971; U.S. Department of the Interior, Bu-
reau of Reclamation, 1974; U.S. Department of the Interior, 1977). These

studies have employed techniques to identify and separate the sources

of salinity. While their estimates vary because of different assump-

tions about salt transport from natural and irrigated areas, they sug-

gest that approximately two-thirds of the salt load (tons/year) and 50
percent of the concentration (mg/l) in the river at Lake Mead originates

from natural point and diffuse sources. Natural factors in the Colorado

River system which can cause salt loading and concentrating effects in-

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clude: the arid nature of the climate; the geology of the basin with

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its vast areas of erodible, salt-yielding shales; the large tracts of

range and forest lands which consume water and then concentrate the

residual salt in less water as it moves by subsurface flow to the river;

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and evapotranspiration losses from marshy areas and phreatophytes along

the river system.

Man's activities contribute salts and then concentrate them through

consumptive uses, such as evapotranspiration losses from irrigated agri-

culture and reservoir surfaces, and through municipal and industrial uses.

In addition, the exportation of high quality water from the basin, and

its diversion for energy development with evaporation of cooling water

in disposal ponds, has the effect of increasing downstream salinity con-

centrations. Because these practices reduce water supply in the river,

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they all contribute to salinity concentration increases in the river as

it flows downstream. Salinity concentration increases are illustrated

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in table 7, p. 32.

Ecosvstem Characteristics

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The Colorado River Basin is a diverse as well as a large ecosystem,

and dividing it into geographical areas requires an analysis of the

types of parameters which could be logically used to characterize the

basin (Parker and Armstrong, 1974). These physical characteristics,

which relate closely to the natural communities, define aquatic and

terrestrial ec~system types. That the Colorado River Basin is a com-

p1ex, and ecologically isolated, system is emphasized by the biologi-

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cal diversity and the great number of unique species. This river sys-

tem has the largest list of rare and endangered fish and wildlife spe-
cies in the United States (see tables 3 and 4).