IMPROVING DETECTION OF BIOTURBATION-INDUCED SEEPAGE PATHWAYS ON A FLOODPLAIN: EAST BRANCH PERKIOMEN CREEK, PA

Geomorphic impact of large terrestrial organisms is often underappreciated and thus rarely considered by geoscientists, as well as civil and environmental engineers investigating fluvial dynamics and slope failure. We used high-resolution geophysical imaging (800 MHz ground-penetrating radar) to identify and map the extent of bioturbation along a stream bank in southeastern Pennsylvania. A large number of mammal burrows (likely produced by groundhog, Marmota monax) occur within 5 m of eroding stream bank and are emplaced into a heterogeneous substrate of fine-grained floodplain soils with root disturbance and weathered bedrock. Within the study site, burrow entrance diameters (n=4) range from 12-27 cm and lead to inclined shafts (30°-48°) oriented toward the stream in a northerly direction (azimuth: 324-036°). Georadar images allowed visualization of subsurface burrow extensions (voids indicated by reversed signal polarity), revealing a possible connection between adjacent structures. Hyperbolic diffractions coincide with transverse burrow segments, as well as buried roots and rock clasts. Intense local zoogeomorphic activity by large semi-fossorial mammals affects sediment transport, vegetation patterns, and persistent seepage pathways, so burrow networks of variable geometry play an important role in stream bank stability. Our findings demonstrate the utility of high-frequency georadar for imaging clay-bearing soils to determine potential sites of enhanced hydraulic piping during storm runoff and extreme flooding. Given limitations of air-borne imaging in densely vegetated sites, this rapid non-invasive geophysical method will serve as the first step in recognizing and visualizing zoogenic impact along riparian ecotones in modern and relict landscapes.