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<br />002383 <br /> <br />of water and can be used to identify its origin and density characteristics. Field measurements of <br /> <br />specific conductance were not taken during most of the 1970? s. Where absent, they were replaced <br /> <br />with lab-measured values. <br /> <br />Dissolved oxygen measurements can give an indication of biological and physical processes at <br /> <br />work in the reservoir, the amount of organic material carried by a water parcel, and its degree of <br /> <br />atmospheric exposure. Oxygen is produced as a byproduct of photosynthetic activity and is <br /> <br />consumed by respiratory and decomposition processes. High oxygen concentrations are therefore <br /> <br />seen near the surface in the early summer when photosynthetic activities are high. Oxygen <br /> <br />concentrations may be depressed at density gradient boundaries or in the deeper portions of the <br /> <br />reservoir due to buildup, at these locations, of autochthonous or allochthonous organic material <br /> <br />subject to bacterial decomposition. <br /> <br />b. Chemical Samples <br /> <br />The collection and analysis of chemical samples is valuable for determining the chemical <br /> <br />composition of the major ionic constituents that comprise the dissolved substances in a body of <br /> <br />water. This information may be used to determine a fingerprint of the water to identify its source, <br /> <br />the degree of saturation of a particular mineral, or suitability for a given use, such as irrigation. <br /> <br />Chemical analysis is frequently the only way to determine the quantity of certain substances in <br /> <br />solution, such as nutrient compounds. <br /> <br /> <br />c. Biological Samples <br /> <br />Biological monitoring in Lake Powell was initiated in 1990 to attempt to establish a link between <br /> <br />chemical and physical characteristics and higher trophic levels. The analysis of these samples has <br /> <br />not been fully completed. Furthermore, most biological activity in Lake powell that would be <br /> <br />identified by the analysis of zooplankton and phytoplankton samples takes place near the surface <br /> <br />06/02/98 <br /> <br />DRAFT <br /> <br />Page 12 of 62 <br />