Soil development by weathering is counterbalanced by losses through erosion. This balance may be disturbed by extreme natural events and human activities, resulting in reduced soil depths, deteriorated soil hydraulic properties, and loss of biogeochemical function. The presence of vegetation, while accelerating soil development is also necessary to maintain soil stability by reducing erosion. Plants require in turn a hydrologically and biogeochemically suitable soil environment to thrive. It is thus conceivable that disturbed soil states may allow lower vegetation carrying capacity, leading to increased erosion and further decline in vegetation and ecosystem function. Such disturbed systems may recover slowly or not at all. We explore these positive feedbacks by employing a minimal model of coupled nonlinear differential equation for the dynamics of soil development, vegetation, and surface hydrology. The model describes a plant compartment, soil carbon, soil depth, and soil moisture, and includes key feedbacks such as plant-driven inhibition of erosion, dynamic changes in rooting depth and soil textural properties as erosion progresses, and vegetation water stress. Results suggest that ecosystem functioning may deteriorate under various climate scenarios that could cause both longer droughts and higher erosion rates. Impact of anthropogenic disturbances such as removal of vegetation and tillage on the mass and energy balances of the soil-plant system and the stability of the systems are also investigated using this modeling framework, with special attention to land use changes in the Southeastern US and soil degradation problems at the Calhoun Critical Zone Observatory (CZO).
Pelak, N. F.; Manzoni, S.; Wang, J.; Bras, R. L.; Porporato, A. M. (2013): Coupled dynamics of soil formation and erosion in natural and agricultural ecosystems. American Geophysical Union Fall Meeting, December 2013, San Francisco, CA.