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<br />0024G4 <br /> <br />12 <br /> <br />nutrient compounds of phosphorus and nitrogen is also performed to determine the level of <br />primary productivity that the reservoir can support and describe nutrient levels in reservoir <br />releases or zones of potential release. <br /> <br />Quarterly lake"wide surveys include the major tributary arms of the Colorado, San <br />Juan, and Escalante Rivers. Occasional sampling is done in mid-Navajo Canyon because of its <br />potential for frequent hypolimnetic hypoxia. Other work on Lake Powell side charmels and <br />embayments has not been part of past programs but could be included in future work. An <br />assessment of the potential effects of dam operations to the water quality of side charmels and <br />embayments should be conducted before establishing a long-term monitoring program for side <br />charmels and embayments. A study by the USGS for this work has been proposed by the <br />GCNRA with external funding. <br /> <br />Heat budget quantification of modeling has been performed to a limited degree by the <br />Upper Colorado Region of the Bureau of Reclamation as part of preliminary studies for <br />selective withdrawal feasibility. The extent of this modeling has been to determine the effects <br />over a two-year period of selective withdrawal. A more elaborate approach to reservoir <br />modeling is needed to determine heat budget effects over a longer period and to help quantify <br />the relative effects of dam operations and those of other hydrodynamic, hydrologic, and <br />climatologic processes. This modeling effort would be very valuable to test the effects of <br />various operational scenarios on short and long-term water quality conditions in Lake Powell. <br /> <br />Biological sampling is performed routinely as a component of the current Lake Powell <br />Water Quality Monitoring Program. Several analyses are performed at the forebay and other <br />selected stations on the reservoir. Chlorophyll concentrations are measured at the reservoir <br />surface to describe the overall levels of primary productivity from photosynthesizing plankton. <br />Discrete samples are taken near the surface for analysis of phytoplankton concentration and <br />community strUcture. Composite samples are collected by vertical tows through the water <br />column for analysis of zooplankton concentration and community strUcture. This information <br />is used to describe long-term and seasonal changes in primary and secondary productivity and <br />describe the type and amount of these organisms in Glen Canyon Dam releases. No work is <br />currently being performed on macrophytes, periphytes, or macro-invertebrates. Evaluation of <br />these shallow-water organisms is more appropriately addressed with a side charmel and <br />embayment water quality assessment. <br /> <br />No work is currently being performed by GCMRC to determine levels of selenium in <br />reservoir water, sediment, or biota. Work is planned, however, on a Colorado River basin- <br />wide selenium study to be performed by the Upper Colorado Region of the Bureau of <br />Reclamation. It is expected that Lake Powell selenium issues will be addressed by BOR and <br />that it will be linked with the existing Lake Powell Water Quality Monitoring Program. <br /> <br />DRAFT - June 17, 1998 <br />