Geomorphic evolution of soil texture and organic matter in eroding landscapes

Geomorphic erosion on hillslopes creates a distribution of soil properties within the landscape that influences ecosystem, erosional, and hydrological processes. These soil properties typically reflect topography and define a template for plant productivity and consequent soil carbon accumulation. Erosion also redistributes soil carbon and, by burying or excavating carbon, changes turnover time and may figure prominently in the global carbon budget [Stallard, 1998]. In this paper, we present the Changing Relief and Evolving Ecosystems Project (CREEP), a theoretical, process-response model that focuses on the redistribution of soil texture and soil carbon along a hillslope in response to geomorphic transport processes. The CREEP model simulates long-term ecological and geomorphic landscape evolution by simulating general soil, vegetation, and hillslope transport relationships. In particular, the model allows for the removal and downslope transport of soil carbon, as well as for the burial and decomposition of carbon in the accumulation zone. CREEP model results suggest that sandy soils are more likely to differentiate downslope with respect to soil texture than are more clay-rich soils and that this redistribution will lead to disproportionately broad areas of predominantly coarse-grained particles on upper slopes. Gridded biogeochemical models, which may otherwise overlook landscape heterogeneity, may use CREEP estimates of the areal distribution of soil texture as a basis for parametrically capturing trace gas fluxes nonlinearly related to soil texture.