NEOICHNOLOGY AT THE SANTA CATALINA CRITICAL ZONE OBSERVATORY: THREE-DIMENSIONAL ANALYSIS OF SOIL FAUNA BURROWS FROM THE SONORAN DESERT, ARIZONA, USA

The purpose of this ongoing project is to record soil and neoichnological properties in a field setting with the infrastructure to quantify variables that correspond to the five soil-forming factors (climate, organisms, relief, parent material, and time). Burrow properties can then be related to climatic and environmental parameters to produce mathematical expressions in order to improve interpretations from fossil burrows. Fieldwork was conducted at the Santa Catalina Critical Zone Observatory near Tucson, Arizona. Three sites were investigated: B2 Desert (B2D), Oracle Ridge (OR), and Marshall Gulch (MG). Mean annual temperature and precipitation range from 18.2°C and 420 mm at B2D (elevation of ~1000 m above sea level) to 10.2°C and 940 mm at MG (elevation of ~2500 m). The land surface of each site was mapped, soils were described, and open burrows were cast with plaster. Burrow casts were measured for standard distances, angles, complexity, and tortuosity and 18 were scanned with a NextEngine laser scanner to produce true scale 3D digital models. Blender was used to measure volume (V) and surface area (SA) from which V:SA ratio, relative compactness, and volume exploited were calculated. Burrows were divided into four types: 1) plug-shaped, 2) J-shaped, 3) vertically flattened tubes, and 4) large-diameter tubes. Burrow diversity decreased with increasing elevation. All types are found in B2D, and only the large-diameter burrows occur at all sites. This may reflect the diversity of fossorial animals at each site—the desert environment likely has a greater number of burrowing animals due to the harsh surface conditions. Burrow V:SA ratios decrease with decreasing elevation resulting from decreasing burrow volume. Animals appear to minimize surface area in harsher settings to prevent moisture loss, but also excavate volumetrically smaller burrows to expend less energy. This trend is not the result of differences in burrow diversity because large-diameter burrows present at all three sites also exhibit the trend. Finally, best-fit lines on volume vs. surface area plots for different burrow types have unique slopes. These slopes are also unique when compared to data from burrows of other tracemakers.