Impact of Land Use on Soil Hydrology in Winter

气候变化正在对加拿大许多地区的冬季土壤水文产生深远影响。例如，冬季中期解冻，这是越来越普遍，可以产生大量的径流（RO）和深排水（DD）的融雪或雨水。土地利用和其他因素对冬季中期解冻期间产生的RO和DD量的影响尚不清楚。直接在现场测量RO和DD的含量并不简单，尤其是在冬季中期短期解冻期间。通过土壤水文模型估算RO和DD需要测量或至少估计土壤水力特性，即土壤水分特性（SWC）、土壤冻结特性（SFC）和水力传导率（K）。这三个关键关系最好在田间测量，以准确反映田间土壤水文条件。然而，它们主要是在实验室中测量的，或者在生长季节不太频繁地在田间测量，在冬季非常罕见。特别是，K已经收到很少，如果有的话，在现场的调查在冻结和解冻条件下，只有少数实验室研究已经进行。为了解决这些知识的差距，本研究的目标是：（一）确定常见的土地利用方式对土壤的SWC，SFC和K在冻结和融化条件下在外地的影响和（ii）将这些属性的时间变异到模拟土壤水文在冬季。拟议的研究将在代表两个不同冬季气候区域的安大略南部和北方实地进行，为期五年，以捕捉冬季气候条件的一些逐年变化。将在每个地区选择田间地点，以代表当地常见的土地利用实践，例如农业中耕作物（包括耕作和免耕）、草地和森林环境。为了最大限度地提高成功的可能性和广泛采用的研究方法，在现场使用的仪器将选择从现有的，商业上可用的设备。在冻融条件下测定土壤SWC、SFC和K，必须测量土壤温度、含水量、电位和土壤水通量。有许多市售的传感器可以测量土壤温度和含水量，但在冻融条件下测量土壤水势更具挑战性。传统上，充水张力计用于测量土壤水势，但它们仅在未冻结的土壤条件下工作;然而，现在可以使用在未冻结和冻结条件下工作的介电传感器。本研究的创新之处在于：（1）没有在冻融过程中对K进行现场测量;（ii）滞后，虽然注意到发生在冻结和解冻在以前的研究，并没有广泛研究使用现场数据，特别是对K和（ii）它将开发新的模型，包括时间变化的SWC，SFC和K作为改进冬季土壤水文模型的第一步。这项研究的直接影响是在提高准确性的洪水预报在仲冬解冻，帮助解释机制，以解释在春季解冻期间温室气体产生的峰值，从定量和定性的角度加强水源水（地表水和地下水）的保护，并提供指导方针，制定适应气候变化的作物管理战略。未来的工作将集中在将空间变异性和扩大这些现象，以改善流域尺度的冬季水文建模。

Climate change is having a profound impact on winter-season soil hydrology in many regions of Canada. For instance, mid-winter thaws, which are becoming commonplace, can generate a significant amount of runoff (RO) and deep drainage (DD) of snowmelt or rain. The impacts of land use and other factors on the amounts of RO and DD generated during mid-winter thaws are not well understood. Measuring the amounts of RO and DD directly in the field is not straightforward especially during short-term mid-winter thaws. And estimating RO and DD through soil hydrology modelling requires measurements or at least estimates of soil hydraulic properties, namely the soil water characteristic (SWC), soil freezing characteristic (SFC) and hydraulic conductivity (K). These three key relationships are best measured in the field to accurately reflect field soil hydrological conditions. Nevertheless, they have mainly been measured in the lab or less frequently in the field during the growing season and only very rarely during the winter season. In particular, K has received very little, if any, investigation in the field during freezing and thawing conditions and only a few laboratory studies have been conducted. To address these knowledge gaps, the objectives of this research are: (i) to determine the impacts of common land use practices on SWC, SFC and K of soils during freezing and thawing conditions in the field and (ii) to incorporate temporal variability of these properties into modeling of soil hydrology in winter. The proposed research will take place at field sites in southern and northern Ontario representing two different winter-season climatic regions for a five-year period to capture some year-to-year variability in winter climatic conditions. Field sites will be chosen in each region to represent common, local land-use practices such as agricultural row crop (including tillage and no-tillage), grass, and forest settings. To maximize the likelihood of success and widespread adoption of the research methods, the instrumentation used in the field will be selected from existing, commercially available equipment. To measure SWC, SFC and K under freezing and thawing conditions, soil temperature, water content, potential, and soil water flux must be measured. There are numerous commercially available sensors that measure both soil temperature and water content, but measuring soil water potential under freezing and thawing conditions is more challenging. Traditionally, water-filled tensiometers are used to measure soil water potential but they only operate under unfrozen soil conditions; however, dielectric-based sensors are now available that operate under both unfrozen and frozen conditions. The proposed research is novel in the following ways: (i) K has not been measured in the field under temporally-variable freezing and thawing processes; (ii) hysteresis, although noted to occur during freezing and thawing in previous studies, has not been investigated extensively using field data, especially for K and (ii) it will develop new models to include temporal variability in SWC, SFC and K as a first step in improving winter-season soil hydrology models. Immediate implications of this research are in improving accuracy of flood forecasting during mid-winter thaws, aid in the interpretation of mechanisms to explain spikes in greenhouse gas production during spring thaw periods, enhance source water (both surface and groundwater) protection from quantitative and qualitative perspectives, and provide guidelines for developing crop management strategies for climate change adaptation. Future work will then focus on incorporating spatial variability and scaling-up of these phenomena to improve modeling of watershed-scale winter season hydrology.