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<br />002J57 <br /> <br />basin upstream from the monument, are a probable source of the trace elements. <br />Concentrations of trace elements would be expected to be larger just down- <br />stream from the source and should then decrease downstream because of dilution <br />from sediments with smaller trace-element concentrations. The secondary <br />bottom-sediment trace-element maximums at site 28 have no obvious explanation. <br />Additional sampl ing .at intervening sampl ing sites during low flow might estab- <br />lish the source of mercury in the bottom sediments and determine the credibil- <br />ity of the larger than expected mercury value observed at site 8 during this <br />reconnaissance. <br /> <br />The study reported here describes selected water-qual ity characteristics <br />during low-flow conditions which probably occur during late summer each year. <br />Low-flow water-quality conditions during August-September 1975 in streams of <br />the Yampa River basin upstream from the monument have been characterized by <br />Wentz and Steele (1976). Supplemental data collected during January 21-22, <br />1978, at sites 1 and 43 (fig. 1) at the upper and lower ends of the study <br />reach indicate a 36-percent downstream increase in stream discharge but no <br />significant change In specific. conductance at this time of year (table 2). <br />Comparable data for the lower Yampa River study reach during other times of <br />the year, particularly during peak-runoff conditions in May and June, would be <br />useful. During periods of high flow, water-quality effects by tributary <br />inflows from numerous side canyons within the monument may be more pronounced <br />than the effects that were documented by the August 1976 reconnaissance. <br /> <br />Table 2.--Supplemental hydrologic data, January 21-22, 1978 <br /> <br />Samp ling site <br /> <br />Variable <br /> <br />Site-- I 43 <br />Day--- 22 21 <br />Timen 1800 1400 <br /> 0.5 1.5 <br /> 520 525 <br /> 7.2 9.8 <br /> <br />Water temperature, degrees Celsius------------- <br /> <br />Specific conductance, micromhos per centimeter <br />at 25 degrees Celsius------------------------ <br /> <br />" <br /> <br />Discharge, cubic meters per second------------- <br /> <br />9 <br />