Footprints in the Landscape: Quantifying Bioturbation in Soils and Paleosols with Multistripe Laser Triangulation (MLT) Technology.

Bioturbation, which results from burrowing and trampling by fauna, influences the rates of pedogenesis, surface stability, and soil geomorphology.  As biota is one of the five soil-forming factors, the study of the abundance, morphologies, and roles of animal, plant, and microbial traces in pedogenesis is important.  Tracks and burrows left by animal activity, however, are seldom studied quantitatively because their irregular, three-dimensional (3D), and complex shapes make them difficult to measure.  Burrow and track volumes, in particular, provide information about porosity, compaction, aeration, drainage, soil turnover, and soil mixing rates; burrow surface areas are informative for gas exchange, water availability, and mineral weathering.  Although burrow volumes and surface areas are useful properties, they are used rarely in studying bioturbation because traditional measurement methods are tedious and imprecise.  This study set out to quantify bioturbation in soils and paleosols through the application of MLT technology.  We used a MLT scanner to obtain 3D digital models of modern and fossil tracks, fossil arthropod cocoons, earthworm castings from paleosols, modern arthropod burrow casts, and fossil and modern vertebrate burrow casts.  We also captured digital models of burrow casts made by arthropods and vertebrates in soil-filled aquaria.  Volumes and surface areas of digital models were measured precisely.  We derived new approaches to quantifying burrow properties, including measurement of burrow density per unit volume of soil, burrow wall roughness, and efficiency of space usage by burrowing animals.  Digitizing and quantifying burrows created by animals in soil-filled aquaria may be particularly useful because the formation time of a burrow can be used to calculate bioturbation rates for a single animal in unit volume per unit time.  MLT technology allows for understanding better the original morphology, volume, surface area, and other metrics of macrochannels and macropores, and how they can be modified through pedoturbation.