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<br />0187 <br /> <br />Bottom Sediment <br /> <br />Selenium concentrations in the fine fraction of bottom sediment (particle <br />size <0.062 mm) exceeded the baseline value (1.4 ~g/g. table 7) at 5 of the <br />13 sites (tables 12 and 13) where samples were collected. The only stream <br />site that had an elevated concentration was on the St. Charles River (site T2, <br />2.1 ~g/g), although the concentration in the Arkansas River downstream from <br />John Martin Reservoir (site A4) was almost equal to the baseline value (table <br />12). All reservoir sites except the Great Plains Reservoirs (site R3) had <br />elevated concentrations, and the concentration at site R3 was equal to the <br />baseline value (table 13). The highest concentrations were in Lake Meredith <br />(site R2, 5.4 ~g/g) and John Martin Reservoir (site R4, 4.2 ~g/g). The high <br />concentration at site R4 may be additional evidence that selenium is being <br />removed from the water and accumulating in the reservoir. This effect could <br />have caused the decrease in selenium concentration in surface water between <br />sites upstream (site A3) and downstream (site A4) from the reservoir (table 8). <br /> <br />Selenium concentrations in the coarse fraction of bottom sediment <br />(particle size <2.0 mm) were less than concentrations in the fine fraction at <br />all stream sites. At reservoir sites, almost all of the sediment was fine <br />enough to pass through either sieve. Therefore, the fine and coarse fractions <br />were nearly identical, and the selenium concentrations were about equal. <br /> <br />The concentrations of lead and zinc in the fine and coarse fractions of <br />bottom sediment from Pueblo Reservoir (site R1) exceeded baseline values <br />(tables 7 and 13). These elements are among the common constituents of mine <br />drainage and may have been transported into the reservoir from sources <br />upstream from the study area. Copper, mercury, and zinc concentrations <br />exceeded baseline values in the fine fraction of bottom sediment from the <br />Arkansas River near Deerfield (site A7) (table 12). The concentrations of <br />chromium and nickel also were high at this site, although less than the <br />baseline values. No source of these trace metals is known to exist in the <br />vicinity of site A7. <br /> <br />Baseline values were not available for organochlorine pesticides in <br />bottom sediment; however, few concentrations exceeded reporting limits in <br />samples collected at reservoir sites in the study area. Chlordane and DDE <br />were identified at all five reservoir sites (table 13). Maximum concentra- <br />tions were 2.0 ~g/kg for chlordane at Pueblo Reservoir (site R1), near the <br />upstream end of the study area, and 1.0 ~g/kg for DDE at Lake McKinney (site <br />R5), near the downstream end. The only occurrence of DDD was at site Rl, <br />which is not affected by irrigation drainage from within the study area. <br />Aldrin was identified at one site (Great Plains Reservoirs, site R3), and <br />dieldrin was identified at two sites (R3 and RS). No other pesticides were <br />detected in any sample. <br /> <br />I <br />r <br /> <br />39 <br />