ZOOGEOMORPHIC IMPACT OF UNGULATES ALONG A SMALL BEDROCK-CONTROLLED CREEK, BUCKS COUNTY, PA

The populations of ungulates have recently increased in many conservation areas along the U.S. Atlantic Coast due to habitat and predator loss. Consequently, the effects of herbivore activity is drawing interest in the geomorphic context, due to their impact on vegetation, edge loading on riparian sediments, and erosional-depositional effects (micro-sliding) along slopes. To determine the zoogeomorphic impact of white-tailed deer (Odocoileus virginianus) on streambank erosion, >50 hoofprints were studied along sections of Neshaminy Creek (Newtown, Pennsylvania). Numerous trackways were observed on stream terraces, slopes, and exposed bottom sections, with slip marks >30 cm long common in wet mud and on slopes. Seventeen hoofprints, impressed mostly in fine gravel, were measured across three segments of Mill Run at Tyler State Park. The metrics included print length (mean: 6.4 cm), width (6.0 cm), and depth (3.3 cm), distance to the stream (<1 m from low-flow pools), as well as azimuths of travel relative to the slope. Three casts of the impressions were taken to determine average sediment removal volume of ~28 cm³ using direct measurement and water displacement technique. The presence of fresh deer prints on steep muddy slopes and uphill of sandy mini-fans suggests substantial zoogeomorphic yield for this drainage segment. Our study provides information on an important erosional agent along the part of the creek undergoing erosion monitoring.