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<br /> <br /> 2000 <br /> 1995 <br />Z <br />0 1990 <br />i= <br />(jj <br />0 <br />a.. 1985 <br />w <br />0 <br />lL <br />0 <br />a: 1980 <br /><l: <br />w <br />>- <br />0 1975 <br />w <br />to: <br />~ <br />i= 1970 <br />en <br />w <br /> 1965 <br /> 1960 <br /> 0 100 200 300 <br /> COPPER, <br /> IN MICROGRAMS PER GRAM <br /> 2000 <br /> 1995 <br />Z <br />0 1990 <br />i= <br />(jj <br />0 <br />a.. 1985 <br />w <br />0 <br />lL <br />0 <br />a: 1980 <br /><l: <br />w <br />>- <br />0 1975 <br />w <br />to: <br />~ <br />i= 1970 <br />en <br />w <br /> 1965 <br /> 1960 <br /> 0 0.1 0.2 0.3 0.4 <br /> MERCURY, IN <br /> MICROGRAMS PER GRAM <br /> <br /> <br /> <br /> <br />2,000 <br /> <br />100 200 300 400 <br />LEAD, IN <br />MICROGRAMS PER GRAM <br /> <br />5,000 10,000 15,000 <br />MANGANESE, IN <br />MICROGRAMS PER GRAM <br /> <br /> <br />ZINC, IN <br />MICROGRAMS PER GRAM <br /> <br />4,000 <br /> <br />6,000 <br /> <br />8,000 <br /> <br />The streambed-sediment samples also provided <br />data on trace elements that were not detected in the <br />water samples (Deacon and Driver, 1999; Apodaca <br />and others, 2000). Tenmile Creek streambed sediments <br />had the greatest concentrations of arsenic, beryllium, <br />chromium, and selenium of the three main streams <br />flowing into Dillon Reservoir, and the Snake River <br />sediments had the most antimony, cadmium, copper, <br />lead, silver, vanadium, and zinc. In the Blue River, <br />uranium concentrations in sediment were highest. <br /> <br />Figure 5. Concentration plotted against estimated year of deposition for trace elements that displayed a <br />concentration spike in the late 1970's and early 1980's, (All concentrations are in micrograms per gram.) <br /> <br />Streambed-sediment concentrations were <br />compared to the concentrations in the sediment <br />cores taken in Dillon Reservoir. Streambed-sediment <br />samples were wet-sieved in the field, and the silt and <br />clay fraction (finer than 0.063 mm) was analyzed for <br />metals. The wet sieving was done to facilitate compar- <br />isons among samples because trace elements tend <br />to be concentrated in the finer grain-size materials <br />(Horowitz and Elrick, 1988), Reservoir bottom- <br />sediment samples were not sieved, however, because <br /> <br />16 Identification of Water-Quality Trends Using Sediment Cores from Dillon Reservoir, Summit County, Colorado <br />