ASSESSMENT OF ZOOGEOMORPHOLOGICAL IMPACT OF SEMIFOSSORIAL RODENTS ALONG A WOODED SOUTHEASTERN PENNSYLVANIA STREAM

Burrowing mammals have a well-recognized impact on both their biotic and abiotic environment, which can trigger or maintain a geomorphic cascade. In southeast Pennsylvania riparian settings, these burrows expel large volumes of sediment (e.g., legacy mud) and contribute to bank destabilization. In this study, eight burrows were surveyed along the Neshaminy Creek in Tyler State Park (Bucks County) to assess the geomorphic role of semi-fossorial rodents. Along a 2-m-high terrace, burrow strike, dip angle and azimuth, as well as distance to streambank were used to identify the trace maker and their contribution to altering terrace permeability structure. The smallest burrow (part of a network) with an average diameter of 6.4 cm, is only 3.58 m from the nearest stream and was likely produced by a small rodent (mouse or chipmunk). The largest burrows 171,000 cm³ in volume and 9 m away from the stream, suggesting groundhog (Marmota monax) activity, which is common in this area. Near-channel burrows terminating below mean water level are attributed to beaver (Castor canadensis), which has been resurgent in this part of the state. Recent rainfall and flooding (Hurricane Ida, 2021) highlighted the role of large voids in riparian terraces as integral elements of the landscape.