Irrigation drainage studies conducted under the National Irrigation Water Quality Program in the middle Green River basin, Utah, by the U.S. Fish and Wildlife Service, U.S. Geological Survey, and Bureau of Reclamation from 1986 to 1989 detected

1
REMEDIATION ACTIVITIES AT STEWART LAKE AND
SELENIUM REDUCTIONS IN BIOTA
Nathan Darnall1, Bruce Waddell1, and Elise Boeke1
However, selenium was still bio-available at
Stewart Lake, and quickly accumulated in fish and
plankton tissues once organisms entered Stewart
Lake.
Spatial distribution of selenium in Green River
fish
Abstract
Study area
Three composite, whole-body common carp samples
were collected from 10 locations on the Green
River near Stewart Lake in 1995 to determine the
spatial extent of selenium contamination. This
historical data, along with more recent data, has
shown the influence of Stewart Lake and Ashley
Creek as sources of selenium to the Green River,
with highest concentrations at the site adjacent
to Stewart Lake (relative river kilometer zero)
and decreasing with distance upstream and
downstream (Figure 6).
Studies conducted in 1986-1990 identified
elevated selenium concentrations in water,
sediments and biota at Stewart Lake, in
northeastern Utah. Since 1997, remediation
actions, based on an adaptive management
approach, have been implemented at Stewart Lake
to reduce selenium in water, sediments, and
biota. These included diversion of drainwater
around the lake, addition of fresh water, ability
to completely drain the lake, and oxidation of
sediments. Selenium concentrations were
monitored in whole-body adult common carp
(Cyprinus carpio) at selected sites within
Stewart Lake and in the Green River from 1995 to
2001 to determine spatial and temporal trends,
and to assess threats to endangered fish. Three
composite samples of carp were collected at two
primary locations in Stewart Lake during all
seven years, and at ten primary sites along the
Green River during six of the seven years. Years
1995 to 1997 were considered pre-remediation and
years 1998 to 2001 were considered
post-remediation for temporal analysis. Spatial
differences in selenium were identified within
Stewart Lake with highest concentrations near
irrigation drains and seeps. Selenium was also
spatially different along the Green River with
highest concentrations adjacent to Stewart Lake.
Selenium concentrations were lower
post-remediation at each of the two primary sites
in Stewart Lake (26 and 36 reduction), and for
most Green River sites (up to 45 reduction).
After four years of remediation, selenium was
still bio-available at Stewart Lake, and rapidly
accumulated in plankton and in fish tissue.
Selenium concentrations in razorback suckers
stocked into Stewart Lake increased 10-fold over
a 32 day period from 0.9 to 9.0 µg/g dry weight
during 2000. Results from this monitoring show
that selenium has declined in biota at some
sites however, this decline may be due in large
part to water management within Stewart Lake that
has reduced lake availability to adult fish and
likely reduced exported contaminated food to the
Green River, rather than significant reduction of
selenium in sediment.
In 2000, 145 hatchery reared razorback suckers
(Xyrauchen texanus) were stocked into Stewart
Lake. Muscle plugs were collected from 5 fish
prior to stocking and analyzed for selenium with
a mean concentration of 0.9 µg/g dw. After only
32 days, the mean selenium concentration
increased 10-fold to 9.0 µg/g dw (Figure 3).
Selenium concentrations declined in Green River
carp after remediation.
For the periods pre-remediation (1995 to 1997)
and post-remediation (1998 to 2001), selenium
concentrations declined in Green River common
carp similar to that observed in Stewart Lake.
For the site adjacent to Stewart Lake, the
geometric mean selenium concentration decreased
significantly from 18.3 to 9.6 µg/g dw ( F1,20
8.77 P 0.0077 ). The Mann-Kendall S
statistic was used to determine trends in
selenium concentrations over the seven years at
each Green River location. Results of this test
showed selenium concentrations were stable at 5
locations, but decreased at 3 locations at the
90 confidence level and at 2 additional
locations at the 80 confidence level (Figure 6).
Figure 3. Selenium concentrations (ppm, dw) in
hatchery reared razorback suckers as a function
of time from initial stocking into Stewart Lake
during 2000.
Selenium concentrations also remained elevated in
most plankton samples after remediation.
Excluding 5 plankton samples collected in 2000 at
or near the Inlet Channel, the geometric mean
selenium concentration decreased slightly between
pre- and post-remediation (16.3 and 14.3 µg/g dw,
respectively) and one-way ANOVA detected no
significant difference between the two periods (
F1,21 1.54 P 0.229 ) (Figure 4). Even those
samples collected near the Inlet, where sediments
are less contaminated and water was predominately
from the Green River, had elevated selenium
concentrations.
1U.S. Fish and Wildlife Service 2369 West
Orton Circle, Suite 50 West Valley City, UT
84119
Special thanks to Joe Gardner and Dave Naftz
(U.S. Geological Survey) and Chris Cline (U.S.
Fish and Wildlife Service) for technical
assistance and editorial review.

Introduction
Figure 1. Map of study location.
Irrigation drainage studies conducted under
the National Irrigation Water Quality Program in
the middle Green River basin, Utah, by the U.S.
Fish and Wildlife Service, U.S. Geological
Survey, and Bureau of Reclamation from 1986 to
1989 detected significantly high concentrations
of selenium in water, sediment, and biota
(Stephens et al., 1988 Peltz and Waddell, 1991
Stephens et al., 1992). At Stewart Lake
selenium entered the lake through subsurface
drains. Selenium concentrations in the drains
were consistently elevated (up to 140 µg/L),
while selenium concentrations in water at the
lake outlet ranged from 1 to 12 µg/L. Selenium
concentrations in 98 of composite whole-body
fish samples collected in Stewart Lake during
1986, 1988, and 1989 were substantially elevated
above 4 µg/g dry weight (dw). In 1991 fish
were collected from 5 reaches of the Green River
to determine whether selenium concentrations were
elevated in fish along reaches receiving selenium
laden surface or subsurface water. Selenium
concentrations in fish varied spatially, with the
highest concentrations detected in fish near the
Stewart Lake/Ashley Creek and Jensen areas
(Waddell and Wiens, 1994). Eighty percent (80)
of these samples exceeded 4 µg/g dw. To
determine selenium concentrations in endangered
fish Waddell and May (1995) developed a
non-lethal tissue collection method. Mean
selenium concentrations in razorback suckers were
33.0 µg/g dw at Ashley Creek ( n 12 ), and 9.7
dw µg/g at the spawning site ( n 9 ).
Ninety-five percent (95) of samples exceeded 4
µg/g dw.
Figure 6. Selenium concentrations (ppm, dw) in
common carp collected from the Green River
relative to distance upstream (depicted by -
symbol), and downstream from Stewart Lake. For
each location, the yellow bars on the left are
pre-remediation (1995 to 1997), while bars on the
right are post-remediation (1998 to 2001). Light
yellow bars indicate stable trend, aqua and grey
bars indicate decreasing trend at 90 and 80
confidence levels, respectively.
Table 1. Location codes, names and relative
river kilometers (from Stewart Lake).

Conclusions
Figure 4. Selenium concentrations (ppm, dw) in
plankton samples collected from various locations
within Stewart Lake between 1995 and 2000.
Selenium concentrations declined in carp at
Stewart Lake after remediation.

• Whole-body selenium concentrations decreased
  significantly in common carp at
• Stewart Lake and in the adjacent Green River
  after selenium-laden irrigation return
• flow drains were removed from Stewart Lake.
• Selenium in endangered Colorado pikeminnow
  decreased slightly post-remediation.
• In Stewart Lake, plankton still accumulated
  selenium to pre-remediation concentrations
• despite influx of clean Green River water.
• Razorback suckers stocked into Stewart Lake in
  2000 showed a 10-fold increase in
• selenium concentrations in one month.
• Selenium is still bioavailable and readily
  accumulates in biota at Stewart Lake despite
• recent remediation activities. Reductions of
  selenium in biota may be attributable to the
• yearly filling and draining of the lake that
  limits fish exposure and subsequent selenium
• accumulation.

Selenium concentrations declined in endangered
fish after remediation.
One hundred and sixty-seven composite, whole-body
common carp samples were collected at six
locations within Stewart Lake between 1995 and
2001. The geometric mean selenium concentration
for all samples was 17.5 µg/g dry weight. Only
two locations, North Overlook ( n 56 ) and
Outlet ( n 66 ), were sampled during all seven
years, and therefore, provide opportunity for
temporal analysis between pre- and
post-remediation. Because selenium
concentrations were significantly different
between the two locations ( F1,120 30.22 P
0.000000 ), analysis for temporal trends was
performed for each site. Selenium concentrations
were significantly different between pre- and
post-remediation at both the North Overlook (
F1,54 22.21 P 0.000018 ) and at the Outlet (
F1,64 24.64 P 0.000005 ), and geometric mean
selenium concentrations decreased 28.9 and 39.4
respectively (Figure 2).
Non-lethal muscle plugs were collected
opportunistically from endangered fish in the
Green River and in Stewart Lake. Selenium
concentrations were significantly higher in
Colorado pikeminnow (Ptychocheilus lucius)
sampled from Stewart Lake when compared to fish
in the Green River near Stewart Lake ( F1,28
8.20 P 0.0078 ) (Figure 5 aqua bars). Fish
sampled further from Stewart Lake generally had
lower selenium concentrations. Geometric mean
selenium concentration in Colorado pikeminnow
from the Green River reach near Stewart Lake
(relative river kilometers 4 to 23) declined
between pre- and post-remediation (5.2 and 3.8
µg/g dw, respectively) but the decline was not
quite significant ( F1,22 3.52 P 0.074 ).

Methods
Fish were collected at 6 locations within Stewart
Lake using trammel nets or Fyke nets, and at 12
sites on the Green River by electro-fishing.
Usually, 3 composite samples consisting each of 5
common carp of similar size were collected per
location. Common carp samples were analyzed for
selenium at Geochemical and Environmental
Research Group via graphite furnace atomic
absorption spectroscopy. Non-lethal muscle plugs
were opportunistically collected from endangered
fish, and analyzed for selenium at Columbia
Environmental Research Center via neutron
activation. Statistical analyses were performed
with NCSS2001 (Number Cruncher Statistical
Systems, Kaysville, UT), and significance was
determined at the 0.05 level.

Literature Cited

Peltz, L.A., and Waddell, B. 1991. Physical,
chemical and biological data for detailed study
of irrigation drainage in the middle Green
River basin, Utah, 1988_89, with selected data
for 1982_87. U.S. Geological Survey
Open_File Report 91_530, 213 pages. Stephens,
D.W., Waddell, B., and Miller, J. B. 1988.
Reconnaissance investigation of water quality,
bottom sediment, and biota associated with
irrigation drainage in the middle Green River
basin, Utah, 1986_1987. U.S. Geological
Survey Water_Resources Investigations Report
88_4011, 70 pages. Stephens, D.W., Waddell, B.,
Peltz, L. A., and Miller, J. 1992. Detailed
study of selenium and selected elements in
water, bottom sediment, and biota associated with
irrigation drainage in the middle Green River
basin, Utah, 1988_90. U.S. Geological
Survey Water_Resources Investigations Report
92_4084, 164 pages. Waddell, B. and May, T.
1995. Selenium concentrations in the razorback
sucker (Xyrauchen texanus) substitution of
non-lethal muscle plugs for muscle tissue in
contaminant assessment. Archives of
Environmental Contamination and Toxicology.
28321-326. Waddell, B. and Wiens, C. 1994.
Monitoring of selenium in fish of the Green
River, Utah. U.S. Fish and Wildlife
Service. Salt Lake City, UT. Unpublished report.
Remediation
Remediation activities began in the spring of
1997 when a new inlet channel was cut into
Stewart Lake, allowing Green River water to flow
through the lake during peak runoff. Later that
same year, drainage channels were excavated in
the lake bed to allow the lake to drain
completely. Finally, irrigation return-flow
drains (the major source of selenium to the lake)
were diverted away from the lake and extended to
the Green River during the winter of 1997 and
spring of 1998. Even though the processes of
flooding, draining, and drying the lake have
continued since 1997, for the purposes of
interpreting the biological data, 1998 represents
the first full field season of new lake
management with the sources of selenium removed.
For statistical analysis, the following
conventions have been used
Pre-remediation
Post-remediation
Figure 5. Selenium concentrations (ppm, dw) in
muscle plugs from Colorado pikeminnow in Stewart
Lake and various reaches of the Green River
relative to Stewart Lake. Geometric mean
selenium concentrations shown in parentheses.
Figure 2. Selenium concentrations (ppm, dw) in
whole-body common carp samples collected from two
locations in Stewart Lake from 1995 to 2001. The
geometric mean selenium concentrations, shown in
parentheses, declined significantly at both
locations between pre- and post-remediation.
1998, 1999, 2000, 2001
1995, 1996, 1997