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000082 basin upstream from the monument, are a probable source of the trace elements, Concentrations of trace elements would be expected to be larger just down- stream from the source and should then decrease downstream because of dilution from sediments with smaller trace-element concentrations. The secondary bottom-sediment trace-element maximums at site 28 have no obvious explanation. Additional sampling at intervening sampl ing sites during low flow might estab- lish the source of mercury in the bottom sediments and determine the credibil- ity of the larger than expected mercury value observed at site 8 during this reconnaissance. The study reported here describes selected water-quality characteristics during low-flow conditions which probably occur during late summer each year, Low-flow water-quality conditions during August-September 1975 in streams of the Yampa River basin upstream from the monument have been characterized by Wentz and Steele (1976). Supplemental data collected during January 21-22, 1978, at sites 1 and 43 (fig. 1) at the upper and lower ends of the study reach indicate a 36-percent downstream increase in stream discharge but no significant change in specific conductance at this time of year (table 2). Comparable data for the lower Yampa River study reach during other times of the year, particularly during peak-runoff conditions in May and June, would be useful, During periods of high flow, water-quality effects by tributary inflows from numerous side canyons within the monument may be more pronounced than the effects that were documented by the August 1976 reconnaissance. Table 2.--Supplemental hydrologic data, January 21-22, 1978 Sampling site Variable Site-- 1 43 Dayn- 22 21 Time-- 1800 1400 0.5 1.5 520 525 7.2 9,8 Water temperature, degrees Celsius------------- Specific conductance, micromhos per centimeter at 25 degrees Celsius------------------------ Discharge, cubic meters per second------------- 9