Thermally-Driven Exchange Flows in Regions of Vegetation

植被区域中热驱动的交换流

• 批准号: 0509658
• 负责人: Heidi Nepf
• 金额: --
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-08-01 至 2010-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0509658&HistoricalAwards=false
• 关键词: Thermally; Driven; Exchange; Flows; Regions

0509658H. M. NepfSpatial heterogeneity in water temperature, and thus density, will drive horizontal flowsthat carry fluxes between chemically distinct regions of a surface water body. The spatialgradients in water temperature may arise from differences in water depth or differences inlight penetration. For example, a spatially uniform heat flux causes the temperaturewithin a shallow region to rise and fall more rapidly than an adjacent deep region. It isnow well recognized that the resulting buoyancy-driven exchange between the littoraland pelagic zones plays an important role in setting lake-scale chemistry and ecology.The presence of emergent and submerged aquatic vegetation is a common feature ofthe littoral region, yet only a handful of studies have considered the impact of vegetationon littoral-pelagic exchange. Because vegetation provides significant drag, it can modifythe thermally-driven exchange current. Indeed, a scale analysis presented in the proposalshows how vegetation can control the rates of exchange. In addition, by partially or fullyshading regions of the water column, the presence of both emergent and submergedvegetation can produce temperature gradients that drive flow between the vegetatedregion and the open water. Because a distinct bio-chemical environment often existswithin the vegetated zone, these exchange flows provide an important hydrodynamic linkbetween biologically and chemically distinct regions of surface water.To fully evaluate the impact of these flows on lake-scale chemistry and ecology, onemust be able to predict their frequency, duration and spatial footprint. The proposedproject will provide this predictive ability. A series of laboratory experiments have beendesigned to observe the formation and magnitude of thermally-driven exchange flowsbetween open water and water with vegetation of different morphology. The velocityfield will be measured using digital particle imaging velocimetry (DPIV). Both emergentand submerged vegetation canopies will be considered. Further, the depth of heatpenetration will be varied using water colorant to block more deeply penetratingwavelengths.The results of the proposed work will enable researchers and lake managers to makebetter evaluations of how changes in the littoral zone, e.g. due to land development, mayimpact the hydrodynamic link between the littoral and pelagic regions, and thus mayimpact the lake-scale nutrient budget and ecology.

0509658H。 M. NEPFF -Spatial异质性在水温下，因此密度将驱动水平流动，在地表水体的化学区域之间携带通量。水温下的空间gratial剂量可能是由于水深差异或差异渗透而产生的。例如，在空间上均匀的热通量会导致温度为浅的区域，而浅层区域比相邻的深区更快地升高和下降。尚不清楚的是，littoraland pelagic区域之间由此产生的浮力驱动的交流在设置湖泊规模的化学和生态学中起着重要作用。出现和淹没的水生植被的存在是沿海地区的共同特征，但只有一些研究才考虑了一些研究的蔬菜植被植被植被的影响。由于植被提供了明显的阻力，因此可以改变热驱动的交换电流。实际上，在提案中提出的比例分析如何控制植被如何控制交换率。此外，通过水柱的部分或全身区域，出现和层压蔬菜的存在都可以产生温度梯度，以驱动植被区域和开放水之间的流动。由于经常在植被区域中存在独特的生物化学环境，因此这些交换流在生物学和化学上不同的地表水区域之间提供了重要的流体动力学联系。为了充分评估这些流动对湖泊规模化学和生态学的影响，Onemust能够预测其频率，持续时间和空间足迹。提出的项目将提供此预测能力。一系列实验室实验已经进行了研究，以观察开放水和水之间的热驱动交换流动的形成和幅度，并具有不同的形态学植被。将使用数字粒子成像速度法（DPIV）测量速度场。两种紧急淹没的植被檐篷都将被考虑。此外，使用水着色剂将变化的热渗透深度将变化，以阻止更深入的渗透波长。拟议工作的结果将使研究人员和湖泊经理能够对沿海区域的变化进行评估，例如。由于土地的发展，可能会影响沿海和上层区域之间的流体动力学联系，从而影响湖泊规模的营养预算和生态学。