Concentration of the radionuclide137Cs in water, sediment, and channel vegetation was determined in a Colorado mountain watershed in 1967. No measurable137Cs was found in stream water. Specific137Cs activity in sediment decreased exponentially with distance from the headwaters. Its concentration was 124 pc/g at the headwaters, where a snowfield has existed continuously since the atmospheric testing of nuclear weapons, to 4 pc/g 5600 meters downstream. Stream vegetation samples also indicated a similar decrease in specific137Cs activity with site location downstream.
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