9317 ‎(2)‎

• UCREFRP Catalog Number: 9317
• Author: Spahr, N. E., L. E. Apodaca, J. R. Deacon, J. B. Bails, N. C. Bauch, C. M. Smith and N. E. Driver.
• Title: Water Quality in the Upper Colorado River Basin, Colorado, 1996-98.
• USFW Year: 2000.
• USFW - Doc Type: Denver.
• Copyright Material: NO

Colorado Plateau and the igneous-
metamorphic geology of the South-
ern Rocky Mountains. Agricul-
tural return flows also contribute to
the greater sediment concentrations
measured at the agricultural sites.

The reference site in the Colo-
rado Plateau also had elevated sedi-
ment concentrations. Any rain or
snowmelt event in these areas tends
to substantially increase the sedi-
ment concentrations of streams and
rivers because of the high erodibil-
ity of the soils.

Z 200
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w
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Colorado Plateau
.--
-
.--
Southern
Rocky
, Mountains
-

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Figure 15. Suspended-sediment
concentrations were greatest in the
agricultural areas of the Colorado
Plateau.

Sediment and water-quality sampling at Reed
Wash. (Photograph by Norman Spahr, U.S. Geolog-
ical Survey.)

,'.
'.

BIOLOGICAL MEASURES INDICATE
THAT UCOL AGRICULTURAL AND
COLORADO PLATEAU MIXED LAND-
USE SITES RANK AMONG THE MORE
DEGRADED SITES NATIONALLY

The elevated nutrient and sediment concentrations found in the agricul-
tural and surrounding areas of the Colorado Plateau help to explain the
prevalence of more tolerant biological species. Algal, invertebrate, and fish
communities in the Colorado Plateau generally consist of species more tol-
erant to nutrients and sediments. These result in higher degradation rank-
ings for all three biological measures. The biological measures in the
Colorado Plateau indicate that agricultural and mixed land-use sites in the
VCaL are above the national average in terms of degradation. These rank-
ings compare VCaL agricultural sites to other NAWQA agricultural sites
and VCaL mixed land-use sites to other NAWQA mixed land-use sites
nationally.

Biological indicator

Site name

Algal
status

Invertebrate
status

Fish
status

Dry Creek
(agricultural site)

Reed Wash
(agricultural site)
Colorado River near Cameo
(Colorado Plateau mixed land use)

D
II
II
II
II

II
II
D
II
II

II
II
D
II
D

Gunnison River near Grand Junction
(Colorado Plateau mixed land use)

Colorado River at State line
(Colorado Plateau mixed land use)

EXPLANATION
Middle 50 percent nationally

Highest 25 percent nationally, most degraded sites

D
.

Explanation of Biological Rankings
The three selected biological indicators respond to changes in stream degra-
dation. Degradation can result from a variety of factors that modify habitat or
other environmental features such as land use, water chemistry, and flow. Algal
status focuses on the changes in the percentage of certain algae in response to
increasing siltation and often is positively correlated with higher nutrient
concentrations in many regions of the Nation. Invertebrate status is the average
of II invertebrate metrics that summarize changes in richness, tolerance,
trophic conditions, and dominance associated with water-quality degradation.
Fish status focuses on changes in the percentage of tolerant fish species that
make up the total number of fish. "Tolerant" fish are reported to thrive in
degraded water quality. For all indicators, higher values indicate degraded water
quality.

Major Findings 19