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

Selenium in Western Colorado

Selenium, a naturally occurring trace element, is common throughout
the Western United States in marine sedimentary rocks. It is an essential
micronutrient for birds, fish, and animals (Mayland, 1994) but at high
concentrations can be highly toxic to fish and wildlife. Selenium can be
very mobile in the environment and the mobility can be accelerated by
irrigation. As irrigation water is applied to soils containing selenium,
the selenium is leached out of the soils and into surface and ground
water. Selenium in wetlands, ponds, and lakes is incorporated into bed
sediment and can be bioaccumulated by wildlife, including fish and
birds (Ohlendorf and others, 1986). Areas of the Western United States
susceptible to selenium contamination from irrigati9n, which include
the Grand and
Uncompahgre Val-
leys in western Colo-
rado, have been
identified by Seiler
and others (1999).
Extensive irri-
gated agriculture is
present in the Grand
and Uncompahgre
Valleys of the Colo-
rado Plateau in west-
ern Colorado (fig. 6).
Irrigation drainage
from these areas may
account for as much
Eastern Western UCOL as 75 percent of the
Uncornpahgre Grand Agriculture selenium load in the
River Valley Valley 2 sites
5 sites' 7 sites' Colorado River near
. Data from Butierand others, 1996. the Colorado-Utah
State line (Butler and others, 1996). It is estimated that 61 percent of the
selenium load to Lake Powell in Utah originates from these agricultural
areas in the UCOL (Engberg, 1999). Primary source areas of selenium
in western Colorado are the western one-half of the Grand Valley and
the eastern side of the Uncompahgre River Valley where the residual
soils and alluvium are derived primarily from the Mancos Shale, a
marine shale containing selenium.
A study in 1991-93 of irrigation drainage in the Grand and
Uncompahgre River Valleys detected relatively high concentrations of
selenium in many surface-water and streambed-sediment samples
(Butler and others, 1996). Concentrations of selenium greater than the
aquatic-life guidelines were also detected in the UCOL surface-water
sampling in agricultural areas during 1995-98 and at one streambed-
sediment sampling site in 1995. Investigations of selenium in western
Colorado for remediation planning are continuing through the U.S.
Department of the Interior National Irrigation Water Quality Program
and the Gunnison Basin Selenium Task Force.

.ffi 1,000
::2't:
:;)-'
~ ffi 100
-,a.
wen
en::2' 10
0-0:
Wa:
~8
Oa:
gJS,1
is::2'
0.1
!;

SURFACE WATER

+

Maximum

USEPA
Median guideline
for protection
of aquatic
life is 5 ~g/L

Minimum

Eastern
Uncompahgre
River Valley
32 sites'

Western
Grand
Valley
30 sites'

UCOL
Agriculture
65 samples at
at 2 sites

~ 100
a:
<9
a:
.W
::2'a.
:;)en
~~ 10
-'a:
~8
a:
u
~
!;

STREAMBED SEDIMENT

Individual
Values

. U.S. Fish
, and Wildlife
guideline
~ for protection
:of aquatic life
is 4 ~g/g

.

Water-Quality Characteristics
of Agricultural Areas

Agricultural land use constitutes
about 5 percent of the Study Unit
area (fig. 6). Within the Southern
Rocky Mountains, agricultural land
is almost exclusively hay mead-
ows. The agricultural areas of the
Colorado Plateau (principally the
Grand Valley near Grand Junction
in Mesa County and the
Uncompahgre Valley near Delta
and Montrose in Delta and Mon-
trose Counties, fig. 6) produce hay,
corn, small grains, dry beans,
onions, melons, fruit, and grapes.
The Grand Valley has about 70,000
acres of irrigated land, and the
Uncompahgre Valley contains
about 86,000 irrigated acres (Butler
and others, 1996). The market
value of agricultural products pro-
duced in Delta, Mesa, and Mon-
trose Counties was about 145
million dollars in 1992 (Bureau of
the Census, 1994). Pesticides,
nutrients, and sediment are water-
quality issues commonly associ-
ated with agricultural land use.

Pesticides were sampled in dif-
ferent media. Pesticides were
investigated in surface water by
periodic monitoring at 2 agricul-
tural sites and a one-time synoptic
sampling at 43 agricultural sites.
Fish were collected once at three
agricultural sites and the tissues
analyzed for organochlorine pesti-
cides. Organochlorine pesticides in
streambed sediments were sampled
once at six agricultural sites.
Ground-water samples were not
collected in the agricultural areas
of the UCOL because ground water
is generally not used for public
water supply in these areas.

Major Findings 15