US - Kenya Doctoral Dissertation Enhancement Project: The Impact of Macropores on the Spatial and Temporal Patterns of Soil Moisture in Dryland Ecosystems of Central Kenya

普林斯顿大学的皮凯利·凯勒将指导他的博士生特伦顿·弗兰兹参加这个博士生强化项目。肯尼亚中部旱地生态系统中的牧民活动正受到土地利用政策变化和气候变化的威胁。20世纪60年代末，S被安置在集体牧场，从根本上改变了他们的游牧生活方式。人们定居下来，再加上医疗保健和人口增长的改善，导致了这片土地的过度放牧。从本地乔草稀树草原到退化的贫瘠地貌的变化对人类种群、野生动物种群、水和能量平衡产生了严重影响。关于水量平衡，对系统的一个影响是降雨分布的变化。该地区的降雨量记录表明，降雨量转向更强烈的罕见事件，而年度总数保持不变。土地利用和气候变化对系统的扰动可以用生态水文模型来解决。旱地生态系统过程由大气、土壤和植被之间的复杂相互作用所支配，这些相互作用通过水的质量平衡紧密耦合。完全分解的地表和地下过程的物理模型需要数值例程和参数化，对于生态水文研究的空间(山坡)和时间(许多植物世代)尺度来说，这些都不是微不足道的。为了降低模型的复杂性，安装了一个水量平衡研究，以经验地从不同的景观斑块类型(裸露的土壤、草地和树木)获得通量项。这项研究的结果揭示了水平衡的一个很强的地下组成部分，白蚁可能在创造通量方面发挥了重要作用。为了解决坡面水平衡的地下分量，本文提出了三项创新的地球物理方法研究。两项研究将使用直流电阻率来跟踪注入土壤介质的水的脉冲。第一项研究将在实验室的均匀沙子中进行，以测试方法和仪器。第二项研究将向白蚁巢穴注入水，以跟踪随着时间的推移水在下游的重新分配。电阻率测量将被用来创建白蚁巢穴水重新分配的大致图景，希望使用解析解来近似这一过程。解析解在生态水文景观模型中的实施是可取的，因为它们将大大降低复杂性。第三项研究将调查多个白蚁巢穴对山坡水分平衡的时间和空间影响。将使用电磁感应(EMI)来获得表层1米土壤的总体电导率的测量数据(5-10公顷)。这些实验将于2009年在肯尼亚中部的姆帕拉研究中心进行。该研究中心主任玛格丽特·金奈德博士将担任该项目的主要合作者。拟议活动的学术价值将是对肯尼亚中部旱地生态系统的山坡水文学进行实地和模型研究。这项创新研究将具体探讨白蚁对山坡水平衡的空间和时间影响。研究结果将被用来证明在更适当的生态水文空间(山坡)和时间(许多植物世代)尺度上对系统的数值模型进行合理简化是合理的。拟议活动产生的更广泛影响将是为姆帕拉研究中心等组织提供分析工具，以解决社区和政府对土地利用和气候变化的担忧。旱地生态系统覆盖了地球20%的面积，对扰动极为敏感。该模型可以运行有关气候变化和土地利用政策的多种情景，为当地社区提供对当前放牧做法和未来政策决策的更准确和更有力的估计。

PI Kelly Caylor of Princeton University will supervise his doctoral student Trenton Franz in this Doctoral Dissertaion Enhancement Project. Pastoralist activities in the dryland ecosystem of central Kenya are being threatened by changes in landuse policy and shifts in climate. In the late 1960?s, native pastoralists were placed on Group Ranches, which fundamentally changed their nomadic lifestyle. The sedentarization of the people coupled with improved healthcare and population growth has lead to overgrazing of the landscape. The change from native tree-grass savanna to degraded barren landscapes has severe implications to human populations, wildlife populations, water and energy balances. With regard to water balance, one impact to the system is the change in the distribution of rainfall. Rainfall records in the region indicate a shift to more intense infrequent events, while annual totals remain unchanged. Perturbations to the system from landuse and climate change can be addressed with ecohydrologic models. Dryland ecosystem processes are governed by complex interactions between the atmosphere, soil, and vegetation that are tightly coupled through the mass balance of water. Fully-resolved physical models of surface and subsurface processes require numerical routines and parameterization that are not trivial to solve for the spatial (hillslope) and temporal (many plant generations) scales of ecohydrologic interest. In order to reduce model complexity, a water balance study was installed to empirically derive flux terms from different landscape patch types (bare soil, grass, and tree). The results of the study revealed a strong subsurface component of the water balance and that termites may play a substantial role in creating the flux. In order to resolve the subsurface component of the hillslope water balance, three studies are proposed using innovative geophysical methods. Two studies will use direct current resistivity to track a pulse of water injected into a soil medium. The first study will be performed in the laboratory in a uniform sand to test the methodology and instrumentation. The second study will inject water into a termite nest to track the redistribution of water downstream over time. The resistivity measurements will be used to create a general picture of water redistribution from termite nests with the hope of using analytical solutions to approximate the process. The analytical solutions are desirable for implementation in an ecohydrologic landscape model as they will greatly reduce complexity. The third study will investigate the temporal and spatial impacts that multiple termite nests have on the hillslope water balance. Electromagnetic induction (EMI) will be used to obtain survey data (5-10 ha) of the bulk electrical conductivity of the top 1 meter of soil. The experiments will be carried out in 2009 at the Mpala Research Center of Central Kenya. The director of the research center, Dr. Margaret Kinnaird, will serve as the host collaborator on the project. The intellectual merit of the proposed activity will be field and modeling studies on the hillslope hydrology of the central Kenya dryland ecosystem. The innovative studies will specifically address the spatial and temporal impacts that termites have on the hillslope water balance. The results of the studies will be used to justify reasonable simplifications to a numerical model of the system at more appropriate spatial (hillslope) and temporal (many plant generations) scales of ecohydrologic interest. The broader impacts resulting from the proposed activity will be to provide groups like the Mpala Research Center with analytical tools to address concerns of the community and government about landuse and climate change. Dryland ecosystems cover 20% of the earth and are extremely sensitive to perturbations. Multiple scenarios on climate change and landuse policy can be run with the model that will provide more accurate and robust estimates on current grazing practices and future policy decisions to local communities.