QUANTITATIVE ANALYSIS OF GROUNDHOG BIOTURBAION CLUSTER IN A STREAM-BANK REGOLITH, BUCKS COUNTY, PA

A set of groundhog (Marmota monax) burrows within a 22-m grid along a small creek (Mill Run, Tyler State Park, Pennsylvania) was investigated in order to determine burrow dimensions and matrix characteristics and to groundtruth previously collected geophysical (800 MHz georadar) images. For ten burrows, entrance diameter and shape, shaft depth, strike, dip, azimuth and proximal distance from the stream bank were recorded. These features, including soil composition near two burrow sites (cluster on the north terrace and an entrance to the south), aided in interpreting geophysical anomalies. The largest burrows in the north included a double entrance with dimensions of 0.29 x 0.22 m and 0.30 x 0.18 m, and reaching a depth of 1.22 m. This system likely forms the primary entrance to a larger network, which may be connected with smaller entrances within the cluster. Smaller burrows (<0.10 m) likely serve other functions or belong to other burrowing mammals (e.g., mice). In comparison, the inclined tunnel of a 0.35-m-wide burrow at the southern site reached a tunnel depth of 0.15 m, which was also the approximate depth of metal rod refusal. The geometry of the burrow likely changed into a more vertical shaft, which was traced to a least 1 m depth in a georadar image. Overall, the soil at a densely bioturbated north site had a fine-grained regolith, whereas the Triassic sandstone exerted more control on bioturbation intensity to the south of the creek. Our study provides important information about near-surface bioturbation heterogeneity and matrix properties that support the results of geophysical imaging, as well as offer insight into zoogeomorphic processes affecting slope stability and hydrologic properties along a small forested stream.