ROLE OF SOIL MACROPORES IN SOLUTE TRANSPORT

The mechanisms of contaminant transport through soils are very complex because of the complicated heterogeneous composition of natural soil formation and the presence of preferential flow pathways due to cracks, fissures, structural peds, wormholes and root channels, which are also known as macropores. Two undisturbed soil samples were used to conduct a flow experiment simulating different rainfall intensities in the laboratory. A four-segment outflow collector system was utilized for this column experiment. Bromide tagged water was used to evaluate the role of macropores on solute transport. In addition, Rhodamine dye was used to mark contaminant flow channels. During the different simulated rainfall intensities, water outflow volumes in different segments varied considerably. For example, the measured outflow was negligible in one segment. The redistribution of outflow was observed due to increase in ponding height of rainwater. For example, in one segment, the outflow volume decreased after fifty minutes by five percent. The outflow concentrations of bromide during the first five minutes were considerably different in different segments of the columns, suggesting the presence of preferential flow. The traces of fluorescent Rhodamine B dye in the soil columns also varied considerably from one segment to other.