Is Static Soil Density a Viable Assumption for Studying Surface Hydrologic Processes?

土壤表面是地面和大气之间的界面。土壤表层条件通过影响降雨入渗和径流、土壤水分蒸发和植物有效水分的储存来影响地球的水文循环。土壤表层的性质随时间变化是动态的。耕作使土壤表层松弛，而车辆交通和雨滴的影响使土壤表层紧实。土壤表层的动态密度和孔隙度特性尚不清楚。此外，土壤表层的动态水力特性几乎是未知的。本研究旨在测量一系列野外条件下土壤表层的动态特性，并评估这些特性对水文循环的影响。推进对这些过程的了解对于了解重要的陆地表面-大气交换（例如，永久冻土释放温室气体和蒸散）至关重要，并可能导致更好的农业用水管理。拟议的研究将使用新开发的热- tdr传感器，提供地表土壤含水量和热特性的同步原位测量。热- tdr传感器也能够测量动态表面土壤密度和孔隙度。拟议的实地和数值实验将解决三个基本问题：1 .松散土壤密度在什么时间尺度上和在多大程度上发生变化？2。是否可以识别模式以促进预测关系的发展，将瞬态密度与其他基本土壤水力和热特性结合起来？3。土壤密度的变化如何直接影响地表-大气界面的水和能量交换以及地下土壤的质量和热量传递？解决这些问题为改变水文科学、加强分析框架和改进预测理论提供了机会。在土壤特性和过程方面的专门知识的指导下，并以新开发的工具为支持，拟议的工作提供了在一系列野外条件下测量动态土壤表层特性的机会。由于土壤密度和孔隙度的知识是研究土壤水力、热、气体传输特性和过程的基础，本研究中取得的新发现为陆地表面、水文循环和生态系统动力学的广泛研究提供了变革潜力。

A soil surface is an interface between the ground and the atmosphere. Soil surface layer conditions influence the Earth's hydrologic cycle by impacting rainfall infiltration and runoff, soil water evaporation, and storage of plant available water. Properties of soil surface layers are dynamic in time. Tillage loosens soil surface layers, while vehicular traffic and raindrop impacts cause soil surface layers to compact. The dynamic density and porosity natures of soil surface layers are not well known. Furthermore, the dynamic hydraulic properties of soil surface layers are almost unknown. This study is designed to measure dynamic soil surface layer properties under a range of field conditions and to evaluate the impacts of these properties on the hydrologic cycle. Advancing knowledge of these processes is critical for understanding important land surface-atmosphere exchanges (e.g. permafrost release of greenhouse gases and evapotranspiration) and could lead to better agricultural water management. The proposed study will use newly developed thermo-TDR sensors to provide co-located, in situ measurements of surface soil water content and thermal properties. Thermo-TDR sensors are also able to measure dynamic surface soil density and porosity. Proposed field and numerical experiments will address three fundamental questions: i. Over what temporal scales and to what extent does loosened soil density change? ii. Can patterns be identified to facilitate development of predictive relationships, incorporating transient density, with other fundamental soil hydraulic and thermal properties? iii. How does shifting soil density directly impact water and energy exchange at the land surface-atmosphere interface and mass and heat transfer in subsurface soil? Addressing these questions provides opportunity to transform the hydrologic sciences, strengthen analytical frameworks and improve predictive theory. Proposed work, guided by specific expertise on soil properties and processes, and supported with newly developed tools, provides the opportunity to measure dynamic soil surface layer properties under a range of field conditions. Because knowledge of soil density and porosity is fundamental to investigation of soil hydraulic, thermal, and gas transfer properties and processes, new discoveries achieved in this study offer transformative potential for wide ranging investigations of land surface, hydrologic cycle, and ecosystem dynamics.