Sedimentary deposits proximal to hilly and mountainous terrain record significant variations in sediment delivery over the last 2-3 million years. These fluctuations have been associated with climate change although the responsible mechanisms are poorly known. In such landscapes, analyses of lake-sediment cores often reveal a complex temperature and moisture history as manifested by the temporal pattern of vegetation regimes. While the influence of vegetation on hydrological processes has been well studied, the role of vegetation in the mobilization and transport of soil into channels is not well understood. Because recent evidence suggests that the mixing and disruption of soils by the activity of biological organisms may play a dominant role in the downslope movement of soil, hillslope evolution may be closely tied to temporal changes in ecosystem properties. As a result, current hillslope characteristics reflect a complex history modulated by climate-related changes in vegetation.
PI will quantify the influence of climate-related vegetation changes on sediment production and hillslope evolution by documenting and modeling the transport of soil and naturally-occurring tracers in field sites with variable paleo-environmental records. At our loess-mantled study sites in New Zealand and the Columbia Plateau, USA, we will use soil stratigraphy, high-resolution topographic data, and detailed characterizations of tephra deposits to quantify paleo-hillslope geometry and characterize soil transport processes. Along hillslope transects, he will use buried tephra deposits as both a marker bed for recording exhumation and a tracer for documenting how hillslope processes mix and displace soil. When combined, soil, paleo-environmental, topographic, and tephra datasets will enable him to test soil transport models and reconstruct how climate change regulated transport rates and hillslope dynamics in the late Quaternary. PI's results will be useful for newly emerging carbon sequestration and transport calculations as well as land management strategies.
