Mobilization and transport of soil particles during infiltration experiments in an agricultural field, Shenandoah Valley, Virginia

Evidence that fine particles mobilized and transported in soils and aquifer s can have a profound influence on contaminant migration has spawned much i nterest recently in understanding colloid transport in natural materials. R epeated infiltration experiments on an initially dry field soil were conduc ted to evaluate rates of mobilization of fine particles over time and to in vestigate the importance of transient-flow events on particle transport. Wa ter flow was measured in zero-tension lysimeters at 25 cm depth. For repeat ed infiltration events and for all plots, water flow sharply increased shor tly after initial pending of water at the soil surface, maintained a relati vely steady level during the period of pending, and decreased gradually the reafter. Particle concentrations measured in the pan lysimeters ranged from 7 mg L-1 to 265 mg L-1 and were typically on the order of 10 to 100 mg L-1 . Greatest particle mass flux was observed during the initial infiltration experiment on each plot. During four subsequent infiltration experiments, a ll conducted within 250 min of the first event, steady mass fluxes were obs erved that were approximately 70% of the average value seen in the first fl ush of water through a dry soil, indicating that the supply of mobile soil particles is only sparingly reduced over closely spaced infiltration events . All peak particle concentrations and mass fluxes occurred near either the rising limb or the falling limb of the water flux hydrograph, presumably r eflecting the movement of air-water interfaces during imbibition and draina ge.