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<br />SAMPLE COLLECTION AND ANALYSIS <br /> <br />Objectives <br /> <br />For this reconnaissance investigation, sample collection was designed to <br />evaluate the chemical quality of water, bottom sediment, and biota in the <br />Arkansas River, selected tributaries, and the alluvial aquifer during peak <br />irrigation return flow, and in selected on- and off-channel reservoirs during <br />and after the irrigation season. Stream sampling sites were limited to <br />existing streamflow-measurement and water'-quality monitoring stations. <br />Because the study area was large, sampling of individual irrigation drains was <br />not included. <br /> <br />Samples of water, bottom sediment, and biota were collected at all <br />surface-water sites. Stream and ground-water sites were sampled in August, <br />when natural streamflow was expected to be low and irrigation return flows <br />were expected to be substantial. Reservoir sites were sampled in June and <br />October to include the waterfowl nesting season and fall migration. Bottom- <br />sediment samples from reservoir sites were collected only in October. Biota <br />samples collected from reservoir sites in June and October included birds, <br />fish, invertebrates, and aquatic plants. Only fish and invertebrates were <br />collected at stream sites in August. The number of samples collected at <br />stream, reservoir, and ground-water sites is listed in table 2. <br /> <br />Samples were analyzed for the constituents listed in table 3. All <br />samples were analyzed for inorganic constituents, primarily trace elements, <br />associated with known irrigation-drainage problems. Reservoir water samples <br />collected in October were analyzed for selected soluble herbicides that may <br />have been applied in the study area. Bottom-sediment and selected biota <br />samples from reservoir sites and fish samples from stream sites were analyzed <br />for selected organochlorine pesticides. Although these pesticides were not <br />being used on agricultural lands in the study area during the study period, <br />they may have been used in the past. Because they are persistent, bioaccumu- <br />late in plant and animal tissue, and have harmful effects on animal popula- <br />tions, analyses of selected samples were necessary to test for the existence <br />of a current (1988) problem resulting from past pesticide usage. <br /> <br />~ <br /> <br />Table 2.--Number of samples collected during the study <br /> <br />Sampling Stream Reservoir sites Ground-water <br /> matrix sites June October sites <br />Water 9 5 7 5 <br />Bottom sediment 8 0 5 0 <br />Birdsl 0 67 52 0 <br />Fish2 17 20 22 0 <br />Invertebrates 5 2 0 0 <br />Aquatic plants 0 8 0 0 <br /> lHost samples are of individuals. <br /> 2Host samples are composites. <br /> <br />20 <br />