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.
