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[38 HAMILTON ET AL. it was dominated by nonnative predators and competitors (Modde, [997). The limited presence of juveniles may be due in part to selenium and other contaminants (Hamilton, 1998). Selenium at Sites The spatial distribution of selenium concentrations in larval endangered fish in the present study demonstrated that the lowest selenium concentration was in larvae col- lected upstream of Stewart Lake Drain at Cliff Creek (2.24 llg/g) and the highest at Stewart Lake Drain (7.04 and 7.4211g/g), with lower concentrations at the downstream sites. This pattern is similar to that in whole body of four species of fish (common carp, Cyprinus carpio; channel cat- fish, Ictalurus punctatus; flannelmouth sucker, Catostomus laripinnis; smallmouth bass, Micropterus dolomieu) reported by Waddell and Wiens (l994b) for five reaches of the Green River. They found selenium concentrations in fish were low at Brown's Park (1.9-3.2 llg/g) and Echo Park (2.7-4.2 llg/g, geometric mean 3.611gjg, n == 3), elevated at Jensen (4.6-2111gjg, geometric mean lO.8 llg/g, n == 3) and Stewart Lake Drain/Ashley Creek area (3.1-49 llg/g, geo- metric mean 12.111gjg, n == 8), and slightly elevated at Leota Bottom (3.6-5.7 llg/g, geometric mean 4.611gjg, n == 3), Sheppard Bottom (3-5.7 llgjg, geometric mean 4.311gjg, n == 3), and Ouray (2.5-7.611g/g, geometric mean 3.5 llg/g, n == 18). Cliff Creek There is no information on selenium concentrations in water, sediment, or biota for Cliff Creek in the NIWQP investigations or USFWS contaminant investigations. Waddell and Wiens (1994a) reported that the Brush Creek drainage, located north of the Stewart Lake Drain! Ashley Creek area, had a substantial selenium contamination prob- lem in biota and was contributing to selenium loading in the Jensen reach of the river. Brush Creek is about 2.5 km upstream of Cliff Creek. Selenium concentrations in larvae collected at Cliff Creek increased over time and were posit- ively correlated with increasing fish total length, thus indic- ating that larvae were accumulating selenium. However, Cliff Creek does not receive irrigation drainage but, at its confluence with the Green River, would be subject to sel- enium input from the river, especially selenium loading from Brush Creek immediately upstream. Larvae in the present study were collected in low or zero velocity nursery habitats, which are the most vulnerable to selenium uptake and cycling in biota (Lemly and Smith, 1987). Stewart Lake Drain Selenium contamination of Stewart Lake and its outflow have been well documented by Stephens et al. (1988, 1992) and Peltz and Waddell (1991), and was probably respon- sible for the elevated selenium concentrations in larvae collected at the Stewart Lake Drain site in the present study. Stephens et al. (1988) reported that selenium concentrations in June and August 1986 in the outflow water were 7 llg,liter and in April and August, 1987 were 6 and 10 llg, liter, respectively. Selenium in sediments of the outflow in [986 were 5.111g!g. Selenium concentrations in fish collected in 1986 from the south side of Stewart Lake were 1611g/g in black bullhead (Ameiurus me/as), 23 llg!g in common carp, and 26 llgjg in green sunfish (Lepomis cyanellus). Stephens et aI. (1992) and Peltz and Waddell (1991) also reported elev- ated selenium concentrations in [988-1989 in outflow water t2-1211giliter) and in fish (1l-2511g/g). They also reported that selenium concentrations in aquatic invertebrates col- lected from the south side of Stewart Lake close to the outlet were lO-1611gjg in three mixed invertebrate samples, 13.5 llgjg in a corixid sample, and 27 llg/g in a predomi- nantly chironomid sample. All of the selenium concentra- tions in aquatic invertebrates were substantially elevated, and above the toxic threshold of 3 llgjg proposed by Lemly (1993) for food organisms consumed by fish and wildlife. The Stewart Lake Drain/Ashley Creek area is the most selenium-contaminated site in the Green River. In 1992, an on-site toxicity test was conducted using water collected from Stewart Lake Drain with 3-day-old fathead minnow (Pimephales promelas), 40 to 60-day-old razorback sucker, and 24-hour-old Ceriodaphnia (Finger et aI., 1994). No appreciable mortality occurred in the lO-day tests with fathead minnow or razorback sucker (lO% mor- tality), but there was a 30% mortality and impaired repro- duction in the Ceriodaphnia test. During these tests, selenium concentrations in outflow water ranged from 3 to 5 llgjliter, which was half of concentrations measured at other times. The lack of effects on razorback sucker is not surprising because the older life stage tested would have been more tolerant of contaminant stresses than if the test were conducted with an earlier, more sensitive, life stage (Rand and Petrocelli, 1985). Moreover, their study involved only waterborne exposure, which for selenium would have caused less stress than if a dietary selenium toxicity test had been conducted (Lemly and Smith, 1987; Lemly, 1993). In contrast, acute toxicity tests with young razorback sucker (7-29 days old), Colorado squawfish (8-15 days old), and bony tail (4-19 days old) indicated that they were very sensitive to a mixture of nine inorganic elements simulating the environmental ratios and concentrations in Stewart Lake Drain in a reconstituted water simulating the Green River (Buhl and Hamilton, 1996). They compared the acute toxicity values with measured concentrations in Stewart Lake Drain and determined that a high potential for ad- verse effects may exist in long-term exposures. In two 90-day chronic toxicity tests, one with razorback sucker and the