NEW DIRECTION IN NEOICHNOLOGY: REAL-TIME GEORADAR IMAGING OF SIMULATED BIOTURBATION

For (semi)fossorial organisms, burrowing offers benefits of thermoregulation, shelter, and reproduction, as well as refuge from predation and environmental stresses. To date, there are no effective means of detecting the initiation and dynamics of burrowing in real time due to challenges in forcing and capturing bioturbation without constrains of enclosures. To address this problem, this research tests the feasibility of real-time ground-penetrating radar (GPR) imaging as a viable non-invasive technique for monitoring bioturbation. Stationary high-frequency (2300 MHz) monostatic GPR antenna was used to record changes in electromagnetic (EM) signal velocity and reflection patterns through time (seconds to minutes) as a function of changing subsurface properties (sediment disturbance, air-filled opening, fluid-filled organism). Variations in EM wave velocity were successfully recorded using time triggering (50 traces/s) and analyzed by simulating bioturbation in dry medium-grained sand using downward and laterally looking antenna. The images were post-processed to analyze signal amplitude patterns related to the initiation and duration of burrowing activity (including the nature of the resulting excavation: open/backfilled). Pulses of insertion of an air-filled tube were reflected in abrupt shifts in reflection geometry and mimic the peristaltic movements of fossorial tracemakers. Time shifts correspond to predictable differences in EM wave velocity between unsaturated background sand (14-15 cm/ns), air-filled tube (30 cm/ns), and fluid- and saturated sand-filled tube (3-5 cm/ns). Furthermore, a polarity reversal accompanies the substrate-void transition, compared to normal polarity of the surface wave (velocity reduction) and subsequent transitions. Our study demonstrates the potential of time-triggered GPR imaging for real-time monitoring of bioturbation and will be applied to experiments with live organisms.