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<br />" <br /> <br />2004 <br /> <br />Methods <br /> <br />. <br /> <br />Water-quality samples were collected at eight sites on the Ar1cansas River and at Lake Creek below Twin <br />Lakes Reservoir in April 1990 through March 1993 (table 1). Samples were collected during all four streamllow <br />regimes throughout the study period. Samples were generally collected in a downstream order with sample <br />collection corresponding to water-parcel travel times. Onsite measurements induded instantaneous discharge, <br />pH. specific conductance, dissolved oxygen. and water temperature. Field ponable meters were used for onsite <br /> <br />chemistry measurements of pH, specific conductance, and dissolved oxygen. Water samples were collected, <br /> <br />preserved, and analyzed according to U.S. Geological Survey standardized guidelines and quality-control <br />procedures for surface-water samples for the detennination of inorganic compounds in filtered water (Sylvester el <br />al., 1985; Ward and Harr, 1990). Water chemistry samples were collected using depth-integrated sampling except <br />during extreme flow conditions. <br /> <br />. <br /> <br />Table 1 near here. <br /> <br />Before each field trip. standard cleaning and rinsing procedures were followed to prepare equipment for <br /> <br /> <br />sampling. TIlls included cleaning with non-phosphate laboratory detergent, followed by three tap-water rinses, a <br /> <br /> <br />rinse with dilute 1 percent hydrochloric acid. and three deionized-water rinses. At the field site, prior to sample <br /> <br /> <br />collection, the equipment was rinsed once with deionized water, once with dilute hydrochloric acid, followed by <br /> <br /> <br />three deionized water rinses. Finally, equipment was rinsed three times with native stream water (Dash and Oniz. <br /> <br /> <br />1995). Sample collection for dissolved cations. including trace metals, included filtering water in the field using a <br /> <br /> <br />0.45 micrometer filter. Samples analyzed for total-recoverable and dissolved cations, including trace metals, were <br /> <br /> <br />acidified in the field with niUic acid. Samples analyzed for anions were filtered in the field using a 0.45 <br /> <br /> <br />micrometer filter. Alkalinity samples were not filtered. <br /> <br />. <br /> <br />6 <br />