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Technical Report

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Arkansas, water quality, DeGray Reservoir, dissolved oxygen


A detailed water quality survey (including trace metals) was conducted on DeGray Reservoir in south west Arkansas from 1969 through 1975. The results of this investigation are used to describe physical and chemical processes which affect the concentration of many of the constituents found in the reservoir and river system. Detailed dissolved oxygen profiles as well as turbidity (% transmittance) profiles were useful in delineating the movement of water through the reservoir. Underflows, innerflows, and overflows were observed during different seasons. The development of a metalimnetic dissolved oxygen minima appears to be related to advective transport within the metalimnion. Metalimnetic dissolved oxygen depletion was most severe during years when spring rains occurred after the onset of stratification. Dissolved oxygen data clearly show the "aging" of a new reservoir. Hypoli- mnetic dissolved oxygen depletion was severe during the early years of impoundment but moderated after 4 years. As expected, iron and manganese were found to correlate well with dissolved oxygen depletion. Other trace metals which were studied did not correlate well with either iron or manganese. Significant correlation was observed for cobalt and nickel, probably indicating their geochemical similarity. The intervention of storm events was found to be the most significant factor in determining the concentration of calcium and other conservative constituents. The calcium concentration clearly drops as storm water enters the reservoir. Other constituents are observed to increase in storm water. Among these are phosphorus and suspended solids (as indicated by turbidity).

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