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<br />INTRODUCTION
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<br />The primary objective of this study was to determine
<br />what concentration changes in major and minor inor-
<br />ganic chemicals would occur in the water of the Arkan-
<br />sas River after the completion of Pueblo Dam.
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<br />Secondary objectives included determining the fate of
<br />selected inorganic chemicals in the reservoir environ-
<br />ment, predicting anticipated water quality changes with
<br />time and changing operation, and evaluating water qual,
<br />ity in terms of criteria for various beneficial uses.
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<br />SUMMARY
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<br />Concentrations of major and minor inorganic chemi-
<br />cals (Ag, Cu, Fe, Mn, Zn, Co, Pb, Cd, Hg, Li, Na, K,
<br />Hg, Ni, Mg, and Ca) were monitored within the dis-
<br />solved fraction and suspended fraction of water of the
<br />Arkansas River from 1972 to 1974 prior to impound-
<br />ment by the Pueblo Dam, and the inlet, outlet, and
<br />pool of Pueblo Reservoir from 1974 to 1976. In addi-
<br />tion, other limnological parameters included dissolved
<br />oxygen, conductivity, pH, turbidity, alkalinity, sulfate,
<br />temperatufe, hardness, chloride, total dissolved solids,
<br />and total suspended matter. Pre-impoundment and im-
<br />poundment sediments were analyzed for K, Na, Ca,
<br />Mg, Li, Cu, Cd, Pb, Fe, Mn, Zn, and Mo and compared.
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<br />The dissolved and suspended levels of all the parameters
<br />average much less than the recommended Of maximum
<br />permissible limits for the beneficial uses of the reservoir
<br />(public water supplies, fisheries, irrigation, and recrea-
<br />tion). Where those criteria exist, on only rare instances
<br />were any individual samples collected that had trace
<br />metal concentrations even approaching, much less ex-
<br />ceeding, the various recognized water use criteria. Dis-
<br />solved oxygen and temperature data indicate nearly
<br />ideal growth conditions for salmonid fishes.
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<br />Interesting seasonal, surface, and spatial trends were
<br />observed for most parameters. Parameters excepted were
<br />those that normally averaged less than detectable limits
<br />such that trends could not be followed, The most fre-
<br />quent seasonal trend observed was the classic high win-
<br />ter values corresponding to slow runoff conditions and
<br />low summer values corresponding to fast runoff condi-
<br />tions (temperature excepted). The data indicate that
<br />the reservoir may be acting as a buffer to the normal
<br />seasonal fluctuations maintaining higher dissolved sol-
<br />ids concentrations later into the spring. Spatial and sur-
<br />face trends indicate that evaporation is having somewhat
<br />of a concentrative effect on all dissolved solids and that
<br />certain metals are being precipitated into the sediments.
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<br />The trends of iron, manganese, and zinc were particu-
<br />larly interesting because their seasonal, surface, and
<br />spatial trends did not seem to follow the classical out-
<br />lines, and these metals frequently showed depth pro-
<br />files with the higher dissolved concentrations occurring
<br />at the bottom. The data for these elements indicate
<br />that there is exchange taking place between the reser-
<br />voir water and the sediments. The sediments at times
<br />released meta I ions into the water, but more frequently
<br />metal ions were taken up by the sediment. The sedi-
<br />ment data support this inference in that they show
<br />that the sediments are being enriched (loaded) in a
<br />number of trace metals (Fe, Mn, Zn, and perhaps Mg,
<br />Cu, Cd, Pb) near the inlet of the reservoir, particularly
<br />near site F. This inlet region of the reservoir appears to
<br />be an important area for the dumping of suspended
<br />ffaction metals and the precipitation of dissolved frac-
<br />tion metals.
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<br />Chemically, the reach of the Arkansas River known as
<br />Pueblo Reservoir could be summarized as the "average"
<br />North American river. The positive implications of the
<br />aforementioned statement are beyond the scope of this
<br />summary.
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<br />APPLICATION
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<br />The results of this study have been and continue to be
<br />of interest to those concerned with and involved in the
<br />assessment and impact of water quality and sediment
<br />changes affecting the Arkansas River as a result of the
<br />formation of Pueblo Reservoir. Continued use of these
<br />baseline data of pre- and post-impoundment conditions
<br />in assessment of future water quality management pro-
<br />grams is inevitable.
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<br />HISTORICAL REVIEW
<br />
<br />In May 1972, Drs. Herrmann and Mahan at USC (Uni-
<br />versity of Southern Colorado) were awarded an NSF
<br />institutional grant by the USC Faculty Research Com-
<br />mittee for the implementation of an operational cap-
<br />ability for heavy metals monitoring and the study of
<br />selected heavy metals in the surface waters of the Ark,
<br />ansas River and selected tributaries. From September
<br />1972 to April 1974, general Iimnological and trace
<br />metal data were collected from two sites along the
<br />Arkansas River. River samples were collected monthly
<br />where the Pueblo Reservoir-North Marina is now situ-
<br />ated (approximately 2 miles upstream from the dam)
<br />and where the Northside (Pueblo northside waterworks)
<br />head gate is located (approximately 3 miles down-
<br />stream from the dam). A 2-year set of data on river
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