To investigate the complex dynamic interactions of colloids, carbon, and Fe oxides and their implications in colloid mobilization and carbon cycling. Specific objectives include: (1) quantify transport of organic matter transport with soil colloids under different redox conditions, (2) collect the small size fractions to quantify the colloids' contribution to carbon transport, (3) collect and analyze field samples to relate mobilization and transport of colloid-organic complexes in the subsurface environments with environmental and land use.