SEDIMENTARY AND ECOLOGICAL INTERACTIONS OF SHORELINE MANAGEMENT AND FERAL HORSES ON CUMBERLAND ISLAND, GEORGIA

People have modified barrier islands in the eastern U.S. for the past few centuries, whether through deforestation, agriculture, shoreline development, or introduction of non-native species. Cumberland Island (Georgia) is no exception in this respect. Before its current status as a U.S. National Seashore, a jetty was constructed there in the late 1800s with the intent of stabilizing an inlet between Cumberland and Amelia Island (Florida). Moreover, non-native livestock were introduced repeatedly to the island, including horses released in the 1940s, which have been feral since. Despite the long-time presence of these human alterations, relatively little research has been done to investigate geological and ecological impacts of the jetty and feral horses on Cumberland, or whether they interact. For this research, we documented long-term changes in sedimentary processes caused by the jetty on the southeastern end of Cumberland Island, while also investigating effects of feral horses in the same area. For this study, we used aerial photos and GIS to map shoreline change related to the jetty and probable nearby feral-horse trails to discern their effects on dunes, salt marshes, and other near-coastal environments. We also examined the jetty and trails in the field for baseline observations. Our results showed a statistically significant difference in beach width north and south of the jetty, with the northern side wider. From aerial photographs, we also mapped 100+ extensive and intersecting horse trails in the dunes and salt marshes near the jetty. We conclude that the jetty and feral horses have affected sedimentological and ecological processes on the southeastern end of the island. The jetty interrupts longshore drift, resulting in less sand movement to and deposition on the beach to its south. Moreover, long-term activities of the horses, such as browsing of vegetation and trampling of coastal dunes, accelerated erosion in these environments. Both factors led to a relatively thin, sand-deprived beach and radically altered salt marshes at the southern end of Cumberland Island.