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I I 1792 The percentages of instantaneous total-recoverable cadmium loads contributed to the Arkansas River from the main stem of the river and from the intervening tributaries in their respective reaches are presented in table 6. These data provide a reasonable estimation of the relative magnitude of cadmium loading in the seven main-stem reaches of the upper Arkansas River Basin. It should be recognized, that at many sites, most total-recoverable cad- mium concentrations were less than the detection limit (< Il!gIL) and were estimated to equal 0.7 I'gIL for the purposes of load computation. Therefore, the cadmium-load contributions from some sources may be overesti- mated. The best example of this relation and the worst case of the inadequacy of the cadmium load estimates is at Lake Creek downstream from Twin Lakes Reservoir, which contributes a substantial amount of the streamflow in reach 2. The total-recoverable cadmium concentration in all of the samples collected at this site was less than the detection limit. Therefore, the estimated loads are more a function of streamflow than of cadmium concentration and are probably overestimated, because the total-recoverable cadmium concentrations were always less than I I'gIL. Downstream from Granite, in reaches 3 through 7, cadmium contributions from tributaries within their respective main-stem reach were relatively small (generally < 10 percent) compared to the main-stem loads (table 6). Table 6 near here. Average percentage of seasonal instantaneous streamflow and instantaneous total-recoverable cadmium load contributed to the downstream main-stem site in a reach by the npstream main-stem site and the intervening tributaries in the same reach, April 1990-March 1993 .~"':,tllF;I'O~~A~ D~~~;l :1'V '3 ~~ ~ .. Subject to Revision,. <;:_ ;)<) NOT QUOTE OR R~L;:~~~ 'o,:,'ding Approval by Dlrel..l0" , ~., U.S. Gsc!o~:col Survey 22