Dam operations are known to have significant impacts on reservoir hydrodynamics and solute transport processes. The Gardiner Dam, one of the structures that forms the Lake Diefenbaker reservoir located in the Canadian Prairies, is managed for hydropower generation and agricultural irrigation and is known to have widely altering temperature regimes and nutrient circulations. This study applies the hydrodynamic and nutrient CE-QUAL-W2 model to explore how various withdrawal depths (5, 15, 25, 35, 45, and 55 m) influence the concentrations and distribution of nutrients, temperature, and dissolved oxygen (DO) within the Lake Diefenbaker reservoir. As expected, the highest dissolved nutrient (phosphate, PO43−-P and nitrate, NO3−-N) concentrations were associated with hypoxic depth horizons in both studied years. During summer high flow period spillway operations impact the distribution of nutrients, water temperatures, and DO as increased epilimnion flow velocities route the incoming water through the surface of the reservoir and reduce mixing and surface warming. This reduces reservoir concentrations but can lead to increased outflow nitrogen (N) and phosphorus (P) concentrations. Lower withdrawal elevations pull warmer surface water deeper within the reservoir and decrease reservoir DO during summer stratification. During fall turnover low outflow elevations increase water column mixing and draws warmer water deeper, leading to slightly higher temperatures and nutrient concentrations than shallow withdrawal elevations. The 15 m depth (540 m above sea level) outflow generally provided the best compromise for overall reservoir and outflow nutrient reduction.

中文翻译：

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大草原水库中不同的大坝流出高度对水温、溶解氧和养分分布的影响

众所周知，大坝运行对水库流体动力学和溶质输送过程有重大影响。加德纳大坝是构成位于加拿大大草原的迪芬贝克湖水库的结构之一，用于水力发电和农业灌溉，众所周知，它具有广泛变化的温度状态和养分循环。本研究应用水动力和养分 CE-QUAL-W2 模型来探索各种取水深度（5、15、25、35、45 和 55 m）如何影响养分、温度和溶解氧 (DO) 的浓度和分布在迪芬贝克湖水库内。正如预期的那样，在两个研究年份中，最高溶解养分（磷酸盐、PO43--P 和硝酸盐、NO3--N）浓度与缺氧深度范围相关。在夏季高流量期间，溢洪道操作会影响营养物质的分布、水温和溶解氧，因为增加的水流速度将流入的水引导通过水库表面，并减少混合和地表变暖。这会降低储层浓度，但会导致流出的氮 (N) 和磷 (P) 浓度增加。较低的取水高度将温暖的地表水拉入水库更深处，并在夏季分层期间降低水库 DO。在秋季周转期间，低流出海拔增加了水柱混合，将较暖的水吸入更深，导致温度和养分浓度略高于浅撤水海拔。