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

and Drake, 1989) and warrant further work, as selenium may inhibit egg
production in [Colorado] squawfish [pikeminnow] and other native fishes of
the Colorado River."
A NIWQP investigation in the lower Colorado River including II locations
between Davis Dam and the U.S.-Mexico international border in 1986 to 1987
revealed elevated selenium concentrations in water, sediment. and biota
(Radtke, Kepner, and Effertz, 1988). Radtke et at. (1988) also summarized
selenium concentrations in samples from five U.S. Geological SUf\'ev stations
monitored as part of the National Stream Quality Accounting :--.ietwork be-
tween 1975 and 1987. They reported that the maximum selenium concentra-
tion was 8 Ilg/L and the median was 3 Ilg/L in the lower Colorado River.
Median concentration in the Gila River above diversions at Gillespie Dam was
51lg/L (maximum 14 Ilg/L) , and near the mouth nearYuma. AZ. was 7,ug/L
(maXimum 16 Ilg/L).
Other studies in the lower Colorado River basin have concluded that
selenium contamination of water, sediment, and biota has occurred, and that
the contamination seems to be from the upper Colorado River basin (Andrews.
King, and Baker, 1997; Bell-McCaulou, 1993; King et at., 1993; Lusk, 1993:
Martinez, 1994; Radtke and Kepner, 1990; Ruiz, 1994: Rusk, 1991: \-Velsh.
1992; Welsh and Maughan, 1994). Each of these studies showed that. although
river concentrations of selenium were low, concentrations in river backwater
areas were elevated and contributing to the exposure of aquatic organisms.
Anderson et at. (1961) predicted that "the use of seleniferous waters down-
stream by other irrigation projects may create additional seleniferous agricul-
tural areas." This prediction apparently has been realized in the form of
seleniferous backwater areas in the lower Colorado River basin that were
derived from the disposal of seleniferous drain waters in the upper Colorado
River basin.
In the NIWQP studies of25 areas in the 15 Western states, the middle Green
River ranked 3rd for the highest median water concentration of selenium. 1 st
for sediment, 1st for fish, and 14th for birds (Engberg, 1998). The Gunnison
River basin/Grand Valley ranked 4th for the highest median water concentra-
tion of selenium, 2nd for sediment, 7th for fish, and 1st for birds. .\lthough the
lower Colorado River VaHey had low selenium in water, it was ranked -I:th for
sediments and 4th for fish (Engberg, 1998), due to selenium loading from the
upper Colorado River basin (Engberg, 1999).
These NIWQP, university, and U.S. Fish and Wildlife Service studies of
selenium contamination of the upper and lower Colorado River basins have
been reviewed in the context of their importance to endangered fish in
Hamilton (1998). He concluded that, based on current studies, selenium was
adversely affecting endangered fish in the Colorado River.

SELENIUM STUDIES WITH ENDANGERED FISH

The Colorado River Fishery Project, a component of the Recoven Imple-
mentation Program for the Endangered Fish Species of the Upper Colorado

1164

Hum. Ecol. Risk Assess. Vol. 5. \:0. 6. 1999