Tuesday, November 14, 2006 - 8:00 AM

3D synchrotron microtomography of soil micropores and biophysical implications.

Stephan Peth1, Rainer Horn1, and Alvin J.M. Smucker2. (1) Christian Albrecht University, Olshausenstr. 40, Kiel, 24118, Germany, (2) Michigan State University, Bogue Street, East Lansing, MI 48824

Soil aggregation formation and functional processes are important mechanisms controlling the unsaturated flux and mineral sorption of organic moieties controlling the long term sequestration of soil carbon (C). However, research during the last 50 years produced few quantitative mechanisms controlling the interactive effects between soil biota and soil physical processes at the micro-scale. Pore network geometries and continuities within soil aggregates determine the flux of air, water and nutrients that control these process-level interactions within microbial microsites. Expanding clay minerals also increase their internal porosities during repeated drying and rewetting (D/W) cycles, adding new micro-pores and fissures that transport and store substantial inorganic and organic substrates within aggregate interiors. Advances in X-ray synchrotron micro-tomography and the development of algorithms that quantify pore demographics within media greatly facilitate detailed pore analyses of soil aggregates at the microsite level. Statistical analyses of pore throat size, pore channel length and connectivity as well as pore size distributions within aggregates will transform our understanding of diffusion processes. Lindquist and Venkatarangan (2000) have developed a suite of algorithms which extract specific pore geometries from 3D data sets. We investigated the accuracy of their algorithms using a simulated image of packed hexagonal spheres. Relative errors between theoretical and numerically computed values were 5%. We extracted cubic subvolumes from these reconstructed 3D images which were analyzed for pore statistical properties. These intra-aggregate pore geometries will be used to numerically simulate previously measured C diffusion rates of 7 x10-4 mm h-1 into aggregates of field and laboratory studies. These new approaches for quantifying the dynamic and spatially heterogeneous pore distributions and connectivities can be combined with 3D HYDRUS and other models to better describe the retention and sorption of soil solutions. Potential applications and drawbacks of the applied algorithms will be discussed.