The effect of macropore morphology of actual anecic earthworm burrows on water infiltration: A COMSOL simulation

Soil macropores impact water infiltration. Due to the complexity of macropore structure, most macropore soil water dynamic simulations use simplified assumptions, such as cylindrical shape macropores, which do not well represent fluid flow in actual macropores. In this study, 3D digitalized structures of actual anecic earthworm burrows are obtained by combining tin casting with a 3D scanner. The in-situ earthworm burrows are imported into finite element numerical simulation software (COMSOL). Based on simulations, the effects of burrow spatial characteristics, such as number (N), length (L), average diameter (Davg), and tortuosity (tau) of partially pene-trating (non-through) and fully penetrating (through) burrows, on water infiltration are clarified. The N value of non-through burrows correlates significantly with preferential flow infiltration rates (r = 1). In addition to the N value, the L value of non-through burrows is an important factor affecting preferential flow infiltration (r = 0.99). For the through earthworm burrows, macroporosity (epsilon p) is the best predictor of Ksat. Unlike Davg and L, the tau of burrows has a low correlation coefficient with Ksat. The increase of adjacent infiltration is N-dependent for non-through burrows and is N-independent for through burrows. These findings demonstrate that actual mac-ropore morphology can be used for numerical simulations, which provides a new pathway forward for pore-scale soil water dynamic research.