8180

• UCREFRP Catalog Number: 8180
• Author: Hamilton, S. J.
• Title: Hypothesis of Historical Effects From Selenium on Endangered Fish in the Colorado River Basin.
• USFW Year: 1999.
• USFW - Doc Type: \
• Copyright Material: YES

Hamilton

River below irrigated areas, and after receiving early spring drainage from
large irrigation tracts between Farmington and Shiprock, contained 700 I-lg/L
(Byers et ai., 1938). One irrigated area near Ship rock in May to June 1936
contained 400 I-lg/L. It was noted by the authors that the high selenium
concentration in the San Juan River was "probably an evanescent condition
brought on by the fact that the early irrigation on the areas above the sampling
point had been started but a few days before." Slightly downstream near
Cortez, CO, drainage from large irrigation tracts between Durango and Cortez
contained 400 I-lg/L, which drained through a "baylet" to the San Juan River
where the water sample was collected. On October 30, 1935 (the end of the
irrigation season), the Sanjuan River at Bluff, VT, had 61lg/L, whereas on
March 25, 1936 (prior to irrigation), it contained Il-lg/L (Byers et at., 1938).
The authors noted that the Sanjuan River received "irrigation drainage from
the large irrigation tracts between Durango and Cortez in Colorado and
Farmington and Shiprock in New Mexico."
Even in the late 1950s and early 196Os, selenium concentrations were
elevated in the Sanjuan River and its tributaries (Scott and Voegeli, 1961). For'
example, early in the irrigation season water concentrations in the San Juan
River and its tributaries ranged from 1 to 3 I-lg/L, but at the end of the
irrigation season they ranged from 10 to 400 I-lg/L.
The influence of high selenium loading in the upper Colorado River was
readily apparent in the lower Colorado River basin. In 1935, concentrations of
selenium in water at Topock, AZ (just north of Lake Havasu) were 3 I-lg/L
(Byers, 1936). On November 13, 1936, the selenium concentration in the
Colorado River at Yuma, AZ, was 41lg/L (Byers et at., 1938). Thus, dilution of
Colorado River by non-seleniferous streams such as the Green and Dolores
rivers, and presumably others such as the Yampa, White, Little Colorado, Bill
Williams, and Virgin rivers, did not reduce the selenium concentration below
detectable concentrations. Several of these rivers contributed little selenium
to the Colorado River because Byers et aL (1938) reported that selenium
concentrations in the Paria River at Lees Ferry, AZ , Little Colorado River at
Grand Falls, AZ, Bill Williams River at Planet, AZ, Salt River at Roosevelt Dam,
AZ , and upper Gila River at Coolidge Dam, AZ, were below detection to
Il-lg/L. However, the lower Gila River at Gillespie Dam, AZ, had 2 J.lg/L.
The terminal sink of a rivers flow is the ocean. Lakin and Byers (1941)
reported that selenium concentrations in the Gulf of California 48 kIn south
of the mouth of the Colorado River were 31-lg/L both in a surface water sample
and in one collected at 55 m depth. They also reported 3 Ilg/L in a surface
water sample collected in the Gulf of California 113 kIn south of the mouth of
the Colorado River. Thus, concentrations of selenium in river water could be
carried substantial distances from the mouth of rivers into ocean waters.

mSTORlCAL LINKS BETWEEN sELENIUM AND FISH IN THE
COLORADO RIVER BASIN

Shortly after the construction of Sweitzer Lake located near Delta, CO, in
1954, die-offs of game fish occurred within a few weeks of stocking (Barnhart.

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Hum. Ecol. Risk Assess. Vol. 5. No.6. 1999