ROLE OF MACROPORES IN SOIL WATER FLOW

In recent years, much attention has been given to the understanding the mechanisms associated with the transport of contaminants to groundwater from surface sources. Of particular concerns is the leaching of nutrients and pesticides to ground water, because high concentrations of these constituents make the ground water unsuitable for drinking-water supply. In general, it is difficult to predict water and solute transport in the subsurface systems due, in part, to the complicated heterogeneous composition of natural soil formation. This difficulty is compounded in soils that contain preferential flow pathways due to the presence of cracks, fissures, structural peds, wormholes and root channels, which are also known as macropores.

The preferential flow under different simulated rainfall rates was studies on an undisturbed soil samples taken from the sandy-loam soil of Ulster County, New York. A four-segment outflow collector system was utilized for this column experiment. Chloride tagged water was also used as a flux to understand the role of macropores in solute transport. During the variable rate of rainfall events, water outflow volumes in different segments varied considerably. In fact, in one segment the measured outflow was negligible. However, during the higher rainfall intensities, 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 5%. Although a uniform chloride concentration was applied, the outflow concentrations during the first five minutes were considerably different in different segments of the columns, suggesting the presence of preferential flow. In addition, Rhodamine dye was used to mark contaminant flow channels. The concentration of high flow areas, as marked by Rhodamine B dye, varied considerably from one segment to other.