MEASURING SOIL WATER FLUXES DUE TO EVAPORATION AND FREEZING

测量蒸发和冻结引起的土壤水通量

• 批准号: 1215864
• 负责人: Robert Horton
• 金额: $ 36.4万
• 依托单位: Iowa State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-08-15 至 2016-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1215864&HistoricalAwards=false
• 关键词: MEASURING; SOIL; WATER; FLUXES; DUE

Robert Horton, Iowa State UniversityJoshua Heitman, North Carolina State UniversityHeat transfer and associated temperature variations are fundamental drivers of water phase changes within the hydrologic cycle. Yet, our understanding of soil water phase changes in the presence of temperature gradients remains limited. Newly-developed instrumentation provides detailed, fine-scale measurements of soil thermal properties, temperature and water content. Combined with conservation of energy and mass, these measurements allow calculation of in situ latent heat sinks and soil water fluxes, thus revealing both time and depth dynamics of soil water phase change. Research will test a central hypothesis about the evaporation process, that the depth of the evaporation front is controlled by the magnitude of the liquid water flux to the front, within a context considering both heat and water transfer. This hypothesis will be evaluated through a series of non-isothermal laboratory experiments using thermo-TDR equipped soil columns for a series of surface boundary conditions and two soil types. Measurements of liquid water and water vapor flux profiles, soil surface temperature conditions, and mass balance will offer unprecedented information about both heat and water transfer occurring with soil water evaporation. Concurrently, research will address a second hypothesis about quantifying soil freezing, that a combined measurement-based energy and water balance can accurately characterize the rate of soil freezing, ice contents, liquid water contents and liquid water fluxes at the freezing front in partially frozen soil. This hypothesis will first be addressed through numerical experiments aimed at testing system-imposed limitations, and microcosm experiments and inverse numerical analysis aimed at adaptation of thermal property measurements for temperatures near the freezing point. Incorporating findings from these studies, the hypothesis will be tested in a series of freezing soil column systems, instrumented with thermo-TDR sensors to measure soil water and ice contents, and associated heat and water fluxes.Soil water phase changes -- evaporation/condensation and freezing/thawing -- drive the hydrological cycle and determine water availability for biological, chemical, and physical processes occurring throughout the terrestrial environment. These phase changes also tightly couple water and energy budgets. They involve both sensible and latent heat transfer, and both liquid water and water vapor fluxes. To date, understanding of the interplay of water and energy fluxes with soil water phase changes remains extremely limited. This research will carefully examine water and energy budgets together using newly developed, fine-scale instrumentation in order to improve understanding of the hydrologic cycle, soil water evaporation, and soil freezing. Implications for this research include improved capabilities for land-surface modeling and remote sensing of surface processes, as well as direct application to understanding carbon and trace gas transmissions and myriad other biogeochemical processes.

爱荷华州立大学的罗伯特·霍顿（Robert Horton），北卡罗来纳州立大学医学的转移和相关的温度变化是水文周期内水相变化的基本驱动因素。然而，我们对土壤水相变化的理解仍然有限。新开发的仪器提供了土壤热性能，温度和水分含量的详细的细节测量。结合节约能量和质量，这些测量值允许计算原位的潜在散热器和土壤水通量，从而揭示了土壤水相变的时间和深度动态。研究将检验有关蒸发过程的中心假设，即在考虑到热量和水的情况下，蒸发前沿的深度受液体水通量向前的大小控制。该假设将通过一系列非静脉实验室实验进行评估，该实验使用配备热TDR的土壤柱用于一系列表面边界条件和两种土壤类型。液态水和水蒸气通量剖面，土壤表面温度条件以及质量平衡的测量将提供有关土壤水蒸发发生的热和水转移的前所未有的信息。同时，研究将解决有关量化土壤冷冻的第二个假设，即基于测量的能量和水平衡可以准确地表征土壤冻结的速率，冰块，液体水含量和液化液在部分冷冻土壤中的冷冻前面。该假设将首先通过旨在测试系统施加的局限性的数值实验，以及旨在适应冰点附近温度的热性能测量值的缩影实验和逆数值分析。从这些研究中纳入发现，该假设将在一系列冰冻的土壤柱系统中进行测试，并配有热-TDR传感器来测量土壤水和冰的含量，以及相关的热量和水通量。土壤水相变化 - 蒸发/凝结和冷冻/融化 - 驱动水文循环，并确定水文可用性，并确定生物学，化学物质的过程，以及整个物理过程。这些阶段变化也紧密地磨合水和能源预算。它们涉及明智的和潜在的传热，以及液态水和水蒸气通量。迄今为止，了解水和能量通量与土壤水相变化的相互作用仍然极为有限。这项研究将使用新开发的精细仪器仔细研究水和能源预算，以提高人们对水文循环，土壤水蒸发和土壤冷冻的了解。对这项研究的影响包括提高土地表面建模的功能和表面过程的遥感，以及直接应用以了解碳和跟踪气体传输以及无数其他生物地球化学过程。