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PI凯利凯勒将指导他的博士生特伦顿弗朗茨在这个博士论文增强项目。肯尼亚中部旱地生态系统的畜牧活动正受到土地使用政策变化和气候变化的威胁。在1960年末？20世纪80年代，当地牧民被安置在集体牧场，这从根本上改变了他们的游牧生活方式。人们的定居，加上医疗保健的改善和人口增长，导致了过度放牧的景观。从原生的树木-草稀树草原到退化的贫瘠景观的变化对人类人口、野生动物种群、水和能量平衡产生了严重影响。关于水平衡，对系统的影响之一是降雨分布的变化。该地区的降雨记录表明，降雨量已转向更强烈的罕见事件，而年降雨总量保持不变。土地利用和气候变化对系统的干扰可以通过生态水文模型来解决。旱地生态系统的过程受大气、土壤和植被之间复杂的相互作用的支配，这些相互作用通过水的质量平衡紧密耦合。完全解决的表面和地下过程的物理模型需要数值程序和参数化，是不是微不足道的解决生态水文学的兴趣的空间（山坡）和时间（许多植物世代）尺度。为了降低模型的复杂性，水平衡研究安装经验得出通量项从不同的景观斑块类型（裸土，草，树）。研究结果表明，水平衡的地下成分很强，白蚁可能在产生流量方面发挥了重要作用。为了解决山坡水平衡的地下部分，提出了三项研究，采用创新的地球物理方法。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中在均匀的沙子中进行，以测试方法和仪器。第二项研究将向白蚁巢中注入水，以跟踪下游水随时间的重新分布。电阻率测量将被用来创建一个一般的水再分配的白蚁巢，希望使用分析解决方案，以近似的过程。的分析解决方案是理想的生态水文景观模型的实施，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对山坡水分平衡的时空影响。电磁感应（EMI）将用于获得土壤顶部1米的整体电导率的调查数据（5-10公顷）。实验将于2009年在肯尼亚中部的Mpala研究中心进行。研究中心主任Margaret Kinnaird博士将担任该项目的主持合作者。 拟议活动的智力价值将是对肯尼亚中部旱地生态系统的山坡水文进行实地和模拟研究。创新的研究将专门针对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合理的简化，以更适当的空间（山坡）和时间（许多植物世代）尺度的生态水文利益的系统的数值模型。拟议活动产生的更广泛影响将是为Mpala研究中心等团体提供分析工具，以解决社区和政府对土地使用和气候变化的关切。旱地生态系统占地球面积的20%，对扰动极为敏感。该模型可以运行关于气候变化和土地利用政策的多种情景，为当地社区提供关于当前放牧做法和未来政策决定的更准确和更可靠的估计。

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.