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0014 . ,.,,' Chlorophyll a samples were collected from near the reservoir surface and from near the reservoir bottom. The sampling depths were the same as the depths at which water samples were collected for chemical analyses. Water samples of 1~2 L of water were filtered through a 0.45-~m filter; the filter was then frozen onsite by using dry ice. Chlorophyll a was extracted in the laboratory by using acetone. The analyses .were made using the chromatography and spectroscopy method, with a correction for pheophytin (Chadwick and Associates, Littleton, Colo., written commun" 1985). Zooplankton samples were collected by lowering an 80-~m-mesh zooplankton net to within a few feet of the reservoir bottom and towing the net to the reservoir surface at a rate of about 2.5 ft/s. Periodically, additional samples were collected by towing the net through the euphotic zone. The net was rinsed thoroughly, and zooplankton were transferred to a bottle and preserved with ethyl alcohol. A replicate sample was collected and analyzed separately. Zooplankton densities are reported as number of organisms per cubic meter. The zooplankton densities reflect the assumption that the filtration efficiency of the net was 100 percent. The data should be interpreted as relative density values rather than true density values, however, because the net's true efficiency ptobably was less than 100 percent (Rawson, 1956). In addition to data collection on Pueblo Reservoir, water samples were collected routinely from the Arkansas River upstream and downstream from the reservoir for analyses of inorganic chemical ,constituents. Specifically, samples were collected from station 07097000; Arkansas River at Portland (upstream station) and station 07099400, Arkansas River above Pueblo (downstream station) (pl. 2), using standard U.S. Geological Survey techniques (Brown and others, 1970; Guy and Norman, 1970; Kister and Garrett, 1983). During 1987, data also were collected in April, June, and October at additional Arkansas River and tributary stations between Malta and Parkdale (pI. 2). RESULTS Selected representative profiles made at sites 3B, 5C, and 7B are graphed in figures 1-9. The data are listed'in tables 2-75 in the section entitled "Water-Quality Data for Pueblo ReseJ;voir" at the back of this report and in tables 76-103 in the section entitled'''Water-Quality Data for the upper Arkans'as River basin" at the back of this report. The data within each section are presented by groups of water~quality constituents. Within each constituent group, the data are presented in downstream order. Specifically, onsite measurements of light transparency ar~ listed in tables 2-8. Profile measurements of water temperature, pH, dissolved oxygen, and specific conduc- tance are listed in tables 9-15. Diel profile measurements are listed in table 16. . 6