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<br />Biota sampling sites were selected to determine maximum concentrations <br />of contaminants associated with irrigation drainage. Biota sampling sites <br />were selected based on inflow and outflow of irrigation drainage water and <br />the availability of biota. Biota sampling on the Gunnison and Uncompahgre <br />Rivers was done at or as near as possible to the water-quality sampling sites <br />on these rivers. <br /> <br />Sites on the Gunnison River (sites 2, 3, and 10), the Uncompahgre River <br />(sites 4 and 9), and at Sweitzer Lake (site 7) were sampled for fish, inverte- <br />brates, and plants during July (table 9). Fish, macroinvertebrates, plants, <br />and plankton were collected when maximum growth rates, maximum water temper- <br />ature, and exposure to irrigation water were occurring. Biota sampling <br />site 10 was considered equivalent to water-quality site lIon the Gunnison <br />River. Three tributaries of the Uncompahgre River, Happy Canyon Creek (site <br />12), Spring Creek (site 13), and Dry Creek (site 14) were sampled for biota <br />because they represented major paths for irrigation drainage from farmlands on <br />the west side of the valley. Because water-quality sampling during 1987-88 <br />indicated that maximum selenium concentrations in Sweitzer Lake may occur in <br />late winter or early spring, additional fish samples were collected from the <br />lake in March 1989 (table 10). <br /> <br />Birds and eggs were collected from the Sweitzer Lake area and from the <br />Escalante State Wildlife Area (site 10) during May, June, and July (table 10). <br />That sampling period was selected based on availability of pre-fledgling birds <br />and bird eggs. Because pre-fledglings generally are confined to a local area <br />until they fledge, trace elements and pesticides in their tissue are obtained <br />from food and water in the area where the birds are reared. An attempt was <br />made to collect pre-fledglings immediately before fledging because older birds <br />would have been exposed to any contaminants present in the area for a longer <br />time period than younger birds. Such collections were not always possible <br />because of time limitations in the sampling effort and considerable predation <br />on young birds. Although developmental abnormalities among embryos in bird <br />eggs cannot be detected before the egg has reached one-half term (Ohlendorf <br />and others, 1986), eggs were collected as soon as they were discovered becau~e <br />of the high risk of predatory loss. Therefore, early collection to ensure <br />that representative egg samples were available for contaminant analysis <br />outweighed the loss of pathological information related to developmental <br />abnormalities. <br /> <br />Sampling Methods <br /> <br />All samples were collected using standard techniques. Water-quality <br />samples for the river sites were collected using depth-integrating samplers <br />and methods described by Edwards and Glysson (1988). At sites that had small <br />discharge (sites 5, 6, and 8), depths were too shallow to use samplers, and <br />representative point samples from the centroid of flow were collected using <br />3-L bottles. Water samples for pesticides were collected from the centroid <br />of flow, when possible, by using the glass sample bottles furnished by the <br />water-quality laboratory. Samples were processed for analysis according to <br />instructions in the Water Quality Laboratory Services Catalog (U.S. Geological <br />Survey, 1986). <br /> <br />34 <br />