A new simulation for modelling the topology of earthworm burrow systems and their effects on macropore flow in experimental soils

Earthworm burrows (i.e. macropores) are organised in burrow systems with various geometric properties. These burrow systems have a significant effect on soil processes, particularly the movement of water in the soil. But the relationships between earthworm burrow systems and their hydraulic properties are not well established because experimental studies of burrow geometry are difficult to perform. Although X-ray computed tomography has revolutionised the 3D description of burrow systems, this method is both time consuming and expensive. This paper presents a new, cheap and rapid approach. A computer model simulating the burrowing behaviour of earthworms was developed from experimental studies. A saturated flow model was then superimposed on the structure of the simulated burrow system to explore the relationships between the burrow systems and their hydraulic properties. Simulations of individual burrow systems were obtained for two different species of earthworm belonging to different ecological groups. Structural parameters of burrow systems (pore space, interconnectedness, connectivity and the number of openings at the limits of the space) were calculated and linked with estimates of permeability using regressions. In our results connectivity gave the best prediction of the difference in permeability between the two sets of burrow systems determined by the burrowing behaviour of the earthworms. Pore space, interconnectedness and the number of burrow openings explained fewer variations.