Soil Aggregate Pores Controlling Water Flux Rates and Retentions of Microbes and Ions.

Soil management practices combined with frequent dry/wet (DW) and/or freeze/thaw (FT) alter intra-aggregate pore geometries controlling sorption and flux rates of gaseous compositions, C and N solutions, nutrient retention and microbial communities among concentric regions within soil aggregates at multiple soil depths. The smoothed particle hydrodynamics (SPH) model, a fully Lagrangian meshless numerical method, is being tested to visualize how established specific pore pathways are frequently trafficked by solutions during repeated DW cycling. Advances in X-ray computer microtomography of intact soil aggregates and undisturbed soil columns provide essential 3D images of intra-aggregate soil pores. These two approaches can be used to significantly characterize micro-pore heterogeneities influencing the fate of E. coli within soil volumes. A sub-millimeter glass bead matrix was established to maintain the intra-aggregate pore integrity of less stable soil aggregates during slow hydration to near saturation and subsequent drying to matric water potentials approaching – 0.1 MPa. A glass bead matrix, 1 mm in diameter could extract up to 98% of Cl- ions and E. coli from aggregates. Laboratory experiments using sterile soil aggregates between 4 and 6.3 mm across were inoculated with E. coli slurries of 104 bacteria in 0.5 mM CaCl2 solution. Chloride replaced the SO4 to maintain aggregate stability and reduce electron donors, for the most accurate measurement of oxygen consumption by E. coli. Aggregates with E. coli were incubated under controlled temperatures and soil water potentials and separated into multiple fractions before identifying distributions of C and N compounds, specific cations, and T-RFLP electropherograms of PCR-amplified 16S rDNA microbial nucleotides. Specific flow rates of bacteria through soil aggregates, their spatial distributions, retention and viability will be reported.