Effects of macropore continuity on water movement and solute transport in a loessial soil

Flow through macropores, created by soil pedogenesis and biological activity, play important roles in soil water and chemical transport on the Loess Plateau. Numerous studies have examined individual macropores and the effects of their size on solute transport, but few have assessed the effects of macropore continuity and of neighboring macropores. This paper describes a laboratory investigation of the effects of macropores with varying degrees and types of continuity on the transport and distribution of solutes in loessial soil columns. Soil columns (2-D, 60 cm high) containing standardized artificial macropores were used to obtain breakthrough curves (BTCs) for input solutions containing 1190 mg/L KBr, and 100 mg/L FD and C Blue #1 (a food dye) under a constant hydraulic head of 8 cm. The types of macropore were: open at both the surface and bottom of the soil column (O-O); open at the surface-closed at the bottom (O-C); and closed at the surface-open at the bottom (C-O). Columns with no macropores served as a control. As expected, in the O-O column the solution reached the bottom rapidly, bypassing most of the soil matrix. The presence of an O-C macropore resulted in weak retardation and much deeper penetration of the bromide and FD and C Blue #1 than in the control columns, but the C-O macropore had little effect on either BTCs or solute distributions. In further tests where neighboring macropores were present, an inclined macropore strongly affected solute concentrations in the profile. Therefore, the type of macropore and the presence of neighboring macropores, all affect soil water flows and solute infiltration parameters.