Tuesday, November 14, 2006 - 8:10 AM

Physical Controls on Greenhouse Gas Emissions at Multiple Spatial and Temporal Scales.

Dennis Rolston, University of California at Davis, Land, Air & Water Resources, Davis, CA 95616-8627

The emission of greenhouse gases from the soil to the atmosphere depends upon several physical, biological, and environmental factors. These controls are generally manifested quite differently at various spatial and temporal scales. At the pore scale, the rates of diffusion of substrates, nutrients, and gases to sites of biological activity and the soil temperature are major controllers of greenhouse gas production or consumption. At the column scale (Darcy scale) or small field plot scale; heat and water flow and convection/diffusion/dispersion processes control the rate of delivery of substrates, nutrients, and oxygen to soil profile layers of greatest biological activity, determine the rate of biological activity, and control the flux of produced greenhouse gases through the soil profile. At the field or landscape scale, similar processes are occurring as at the Darcy scale, but due to high spatial and temporal variability many of the physical processes, must be manifested through gross soil properties indirectly affecting biological processes. At the pore or microbial colony scale, physical processes operate on the temporal scale of seconds to hours. At the Darcy scale, these processes operate on a scale of hours to weeks, and at the landscape scale, months and years are most important. These various spatial and temporal scales come forth in the types of models that are being used for predicting greenhouse gas emissions. Examples of model types designed to operate at various scales and their applications to testing and comparison with field data will be discussed