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(P329) Remediation activities at Stewart Lake and selenium reductions in biota.
Darnall, Nathan*,1, Waddell, Bruce1, Boeke, Elise1, 1 U.S. Fish and Wildlife Service, West Valley City, UT
ABSTRACT- 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 bioavailable 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 ppm 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 at Stewart Lake.
Key words: selenium, monitoring, remediation, endangered fish
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