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<br />The direct effects of climatic variability, inclu(Jing the present drought, on the <br />physical and chemical conditions in Lake Powell, including the forebay, can be evaluated . <br />using GCMRC's monthly sampling of the forebay and quarterly sampling throughout the <br />lake. To determine if the climatic effects and the effects of varying water level on Lake <br />Powell are properly understood, the BaR CE-QUAL-W2 model should be used to <br />simulate the recent drought and the output from the model should be compared with the <br />recent data collected in the lake. <br /> <br />Changes in water temperature that occurs as water moves down the canyon is <br />measured at various locations; however, changes in nutrient concentrations are not <br />presently included in the program. The BaR is in the process of developing a sub <br />program in the dynamic model (CE-QUAL- W2) to simulate the changes in water quality <br />as the water flows downstream. GCMRC will collaborate on this model development. <br /> <br />Changes in the hydrology, water temperatures, and nutrient concentrations <br />downstream of the dam will significantly impact the Colorado River ecosystem. This <br />information can be used to predi~t changes that may occur with the implementation of the <br />temperature control device and what could occur in future long-term droughts. These <br />changes include, but are not limited to, changes in metabolism throughout the river, <br />changes in rainbow trout and humpback chub recruitment, changes in the food base, etc. , <br />To examine all of the impacts of the drought requires input from all of the disciplines <br />within the GCMRC and will foster interdisciplinary collaboration, Specific monitoring <br />needs for these other key questions are discussed elsewhere. <br /> <br />Question: How will recent changes in water temperature affect distribution and <br />trophic interactions of native and exotic fishes? <br />Question: How will HBC and RBT respond to varied nows, temperatures, and <br />population? <br />Question: How do CRE biotic resources such as HBC and RT respond to changes <br />in water quality? <br /> <br />. <br /> <br />NeedlRationale: This issue is of immediate relevance in two respects. First, the <br />proposed development of the Temperature Control Device at Glen Canyon Dam is <br />moving forward to the implementation phase. Second, dropping water levels during 2004 <br />put the Lake Powell metalimnion at the depth ofGCD penstocks, and river water now <br />warms in response. <br /> <br />Approach: Temperature monitoring and prompt reporting of results are essential <br />,in this year and the next several years of low lake levels. So, too, are the distribution and <br />numerical responses of key biological resources such as the humpback chub, its prey <br />resources, competitors and predators as well as rainbow trout. Special attention will be <br />directed to effects on rainbow trout below the dam, the ongoing removal of exotics above <br />and below the LCR, and recruitment success of HBC at the LCR. Other concerns include <br />the upstream migration of brown trout from the Bright Angel region, plus similar <br />responses of coolwatcr fishes (e.g., walleye) and warmwater fishes (e,g" striped bass, <br /> <br />USGS SBSC GCMRC Strategic Science Plan - FY 2005-2009 <br />Draft, October 22, 2004 <br /> <br />. <br /> <br />16 <br />