8277

• UCREFRP Catalog Number: 8277
• Author: Bauch, N. J. and N. E. Spahr.
• Title: Pesticides in Surface Waters of the Upper Colorado River Basin, Colorado, 1996-98.
• USFW Year: 2000.
• USFW - Doc Type: Water-Resources Investigations Report 00-4005,
• Copyright Material: NO

affect human health and aquatic ecosystems. In the
UCOL, water samples were collected at four sites
(fig. 1) during 1996-98 to determine temporal and
spatial variations in the occurrence and concentrations
of pesticides. A synoptic study of 43 sites (fig. 2) was
completed in 1998 to determine the spatial distribution
of pesticide concentrations within agricultural areas of
the UCOL.
Purpose and Scope
The purposes of this report are to (1) describe
pesticide concentrations in rivers, streams, and drains
in the UCOL study unit during 1996-98 and (2) deter-
mine the distribution of pesticide detections and
concentrations among different land uses, site types,
and agricultural subbasins in the study unit. Surface-
water sites in the UCOL basin were sampled, and
samples were analyzed for a series of pesticide
compounds to temporally and spatially describe pesti-
cide concentrations. Four river and stream sites in the
study unit were sampled frequently for up to one year.
Forty-three river, stream, and drain sites in agricultural
areas of the study unit were sampled once during a
synoptic study.
Description of the Upper Colorado River
Basin study unit
The UCOL study unit has a drainage area of
about 17,800 mid (fig. 1), all located in western Colo-
rado except for about 100 mi'` in eastern Utah (Driver,
1994). The study unit is divided almost equally into
two physiographic provinces-the Southern Rocky
Mountains in the east and the Colorado Plateau in the
west (fig. 1). The environmental setting of the UCOL
study unit and its physiographic provinces has been
described by Apodaca and others (1996).
Land uses in the UCOL study unit include
rangeland or forest, mining, urban, and agriculture.
Rangeland or forests make up about 85 percent of the
study unit area and are used for recreation, wildlife
habitat, livestock grazing, and logging. Tourism and
recreation are the major land-use activities in the
Southern Rocky Mountains province, and agriculture
is the predominant land-use activity in Delta, Mesa,
and Montrose Counties in the Colorado Plateau.
Tourism, recreation, and agriculture are all important
land-use activities in Gunnison County, located mostly
in the Southern Rocky Mountains physiographic prov-
ince. Because of the semiarid climate (generally, less
than 10 in/yr of precipitation in the western valleys),
little agricultural production is possible without irriga-
tion. Irrigation takes place mainly in river valleys and
in low-altitude areas of the Colorado Plateau. In the
Grand and Uncompahgre River Valleys (fig. 2), agri-
cultural areas are supported by an extensive system of
canals and ditches. About 97 percent of the off-stream
water use in the study unit is for irrigation (Apodaca
and others, 1996).
The major crops produced in the study unit are
alfalfa and other hay, corn (grain and silage), dry
beans, grains, vegetables (primarily sweet corn and
onions), fruit (apples, tart cherries, peaches, and
pears), melons (cantaloupe and watermelon), and
grapes for wine production. Acreage and production
data for Colorado in 1997 are available by county for
alfalfa, other hay, corn (grain and silage), dry beans,
winter and spring wheat, barley, and oats (Colorado
Department of Agriculture, 1998) and are shown in
table l for 10 counties in the study unit. Alfalfa and
other hay together were the major crops produced in
each county in 1997 and were the only crops tallied for
Eagle, Grand, Gunnison, Ouray, Pitkin, and Summit
Counties. Dry beans and corn also were commonly
harvested in Delta and Montrose Counties, while corn
and winter wheat were commonly produced in Mesa
County in 1997. Most (97.6 percent) of the harvested
acreage was irrigated. Alfalfa, other hay, and winter
wheat were produced on the nonirrigated land.
Acreage and production data for individual counties
were not available for vegetables, fruit, melons, and
grapes.
Pesticide-use data for the 1996-98 sampling
period were not available for the study unit. Pesticide
use by crop type in Colorado was estimated by
Bohmont (1991, 1993) for seven regions in the State
for l 989 and statewide for 1992. In the ] 989 survey,
four counties (Garfield, Mesa, Delta, and Montrose) of
the UCOL study unit were represented as the West
Central agricultural region. Ouray County was
included in the Four Corners region, and no pesticide-
use data were reported for Eagle, Grand, Gunnison,
Pitkin, and Summit Counties. The six most common
pesticides applied to irrigated crops in the West
Central agricultural region in 1989 were (1) EPTC,
(2) alachlor, (3) 2,4-D, (4) parathion-ethyl [parathion],
(5) metolachlor, and (6) atrazine, as measured by
INTRODUCTION