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<br />summer-flow periods. The temporal variations in the
<br />percentage of dissolved and suspended fraction of iron
<br />downstream from Terrace Reservoir were similar to
<br />the temporal variations that occurred upstream from
<br />the reservoir. Generally, the temporal variations in
<br />the percentage of dissolved and suspended copper
<br />transported into and out of Terrace Reservoir were
<br />similar to the temporal variations that occurred with
<br />the percentage of dissolved and suspended iron that
<br />was transported into and out of Terrace Reservoir.
<br />With the exception of the pre-peak snowmelt period,
<br />the temporal variations in the percentage of dissolved
<br />and suspended fraction of copper downstream from
<br />Terrace Reservoir were similar to the temporal
<br />variations that occurred upstream from the reservoir.
<br />During the entire study period, cadmium, manganese,
<br />and zinc generally were transported into and out of the
<br />reservoir predominantly in the dissolved fonn.
<br />Logarithms of metal concentrations generally
<br />were not significantly correlated with streamflow or
<br />the logarithm of specific conductance. Correlations
<br />between the logarithms of metal concentrations and
<br />pH generally were strong upstream and downstream
<br />from the reservoir. However, downstream from the
<br />reservoir, scatterplots of the data indicated that a
<br />linear relation did not exist between pH and the
<br />logarithms of the metal concentrations. Correlations
<br />and scatterplots between the logarithms of metal
<br />concentrations and pH upstream from the reservoir
<br />indicated that a linear relation existed. The correla-
<br />tions generally indicated that between 65 and
<br />83 percent of the variation in metal concentrations
<br />could be explained by pH. The metals of concern
<br />were significantly correlated with one another.
<br />Because the correlatiollS among the logarithms of
<br />the concentrations of metals generally were good,
<br />copper was used as the indicator constituent to
<br />detennine the divisions for the time intervals for
<br />estimating aluminum, iron, cadmium, manganese,
<br />and zinc loads.
<br />Metal loads varied considerably as a result
<br />of changes in streamflow or changes in metal concen-
<br />trations, or both. The largest daily loads of aluminum,
<br />iron, and manganese were transported into and
<br />out of Terrace Reservoir during the peak snowmelt
<br />period. The smallest metal loads occurred during the
<br />base-flow period between November 1994 and
<br />February 1995. About 81 percent of the 363 tons of
<br />
<br />total aluminum that entered the reservoir remained
<br />in the reservoir, indicating that the reservoir was a
<br />sink for an estimated 294 tons of aluminum. About
<br />75 percent of the 790 tons of total iron that entered
<br />the reservoir remained in the reservoir, indicating that
<br />the reservoir was a sink for an estimated 596 tons of
<br />iron. The maximum daily total-copper load entered
<br />the reservoir on June 8, about a week later than the
<br />maximum daily total-aluminum and total-iron loads.
<br />The largest copper loads were transported into and
<br />out of the reservoir during the post-peak snowmelt
<br />period. Overall, during the study, an estimated
<br />39 tons of total copper was discharged from the
<br />reservoir downstream to the Alamosa River, and
<br />about 22 tons of total copper remained in the reservoir.
<br />Between April I and November 7, 1994, the period
<br />when the reservoir was releasing water, the total-
<br />copper load transported out of the reservoir was about
<br />64 percent of the total-copper load transported into the
<br />reservoir. About 90 percent of the total-manganese
<br />and total-zinc loads that entered the reservoir was
<br />transported out of the reservoir, indicating that the
<br />reservoir was a sink for only a small fraction of
<br />manganese and zinc.
<br />
<br />SELECTED REFERENCES
<br />
<br />Balistrieri, L.S., Ortiz, R.F., Briggs, P.H., Elrick, K.A.,
<br />and Edelmann, Patrick, 1996, Metal fluxes across
<br />the sediment-water interface in Terrace Reservoir,
<br />Colorado: U.S. Geological Survey Water-Resources
<br />Iovestigations Report 96-040, 83 p.
<br />Boyles, J.M., Cain, Doug, AlIcy, W., and Klusman, R.W.,
<br />1974, Impact of Argo ThnnelllCid mine drainage,
<br />Clear Creek County, Colorado, in Proceedings-Water
<br />Resources Problems Rclated to Mining: American
<br />Water Resources Association, Proceedings 18,
<br />p.41-53.
<br />Cain, Doug, 1995, Factors affecting surface-water quality in
<br />the Alamosa River Basin, south-central Colorado, in
<br />Posey, H.H., Pendleton, J.A., and Van Zyl, D., cds.,
<br />Proceedings-Summitville Forum '95: Denver,
<br />Colorado Geological Survey Special Publication 38,
<br />p.159.
<br />Church, S.E., 1993, Geochemical and lead-isotopic studies
<br />of stream and river sediments, AIamosa River Basin,
<br />Colorado: U.S. Geological Survey Open-File
<br />Report 95-250, 73 p.
<br />
<br />SELECTED REFERENCES 37
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