We studied piping plovers (Charadrius melodus Ord) on Assateague Island National Seashore, Maryland, during the 1988-1990 breeding seasons. The estimated breeding population declined from 25 pairs in 1988 to 14 pairs in 1990. Nest predation by red foxes (Vulpes vulpes) was high. Predator exclosures constructed around individual nests did not increase nest survival. Chick survival was higher in bay beach and island interior brood-rearing habitats than on the ocean beach. Our evidence supports the hypothesis that the availability of adequate food is driving the differences in survival observed among brood-rearing habitats. Chicks raised on the bay beach or island interior weighed more, had higher foraging rates, and spent a greater proportion of their time foraging than chicks reared on the ocean beach. Indices of invertebrate prey abundance indicated that insects were more abundant on the bay beach and island interior than on the ocean beach. Disturbance did not differ among brood-rearing habitats. Human disturbance was higher in 1990 than in previous years. Overall productivity was 0.71 chicks fledged/breeding pair, well below our estimate of the productivity needed to deter a population decline. Management efforts should focus on reducing nest predation and maintaining overwash access paths to high quality brood-rearing habitat. / Master of Science

The National Park Service (NPS) monitors off-road vehicle (ORV) use in National Seashores across the United States. The sediment disturbance that is caused by ORVs is believed to have a large impact on erosion (by wind or waves), which there by affects the morphology of the foredunes. With greater knowledge of ORV impacts, the NPS can better manage ORV use and minimize anthropogenic affects to the coastal environment. There remains considerable uncertainty about the disturbance and its larger-scale impact. This study quantifies the sediment disturbance made by tire tracks, as well as the tire track form, width, depth, and evolution with relation to the number of vehicle passes and location on the beach at Assateague Island National Seashore (ASIS), Maryland. To measure ORV impact, ground-based LiDAR was used to collect detailed profiles across a three by three meter test plot at each site. Based on the quantification of the displaced sediment and redistribution of that sediment from the tracks, a recommendation to the NPS can be made as to where along the beach traffic should be limited to, in order to minimize impact to the physical environment at ASIS. Tire tracks were found to widen after the first pass, as a result of the imperfections of driving. Compaction of the sediment in the center of the tire track accounts for only a minimal amount of the sediment lost from the tire tracks. Sediment removal accounted for greater than 75% of the sediment lost from the tire tracks at all sites. It was concluded that sediment removal is the most dominant factor in the creation and evolution of a tire track. The width, depth, and evolution of a tire track were also found to be controlled by the imperfections of driving. Despite the amount of sediment disturbance, it is found that there is no net downslope displacement of sediment. This conclusion counters previous ORV impact studies and suggests that ORVs are not directly responsible for beach erosion. It is also recommended that to minimize the impact of OVRs on the beach at ASIS, the NPS should limit driving to the backshore.

The objective of this study is to quantify the accuracy of two engineering models for dune erosion (SBEACH and EDUNE), and to determine which of the two models is best suited for predicting barrier island vulnerability due to extreme storm events. The first model, SBEACH, computes sediment transport using empirically derived equations from two large wave tank experiments. The second model, EDUNE, theoretically relates excess wave energy dissipation in the surf zone to sediment transport. The first mechanism for model comparison is sensitivity testing, which describes the response of the model to empirical, physical, and hydrodynamic variables. Through sensitivity tests, it is possible to determine if responses to physical variables (e.g. grain size) and hydrodynamic variables (e.g. wave height) are consistent with theoretical expectations, and whether the function of each variable is properly specified within the governing equations. With respect to empirical parameters, model calibrations are performed on multiple study sites in order to determine whether or not the empirical parameters are properly constrained. Finally, error statistics are generated on four study sites in order to compare model accuracy. Cross-shore profiles of dune elevation are extracted from coastal lidar (light detecting and ranging) surveys flown before and after the impact of major storm events. Three study sites are taken from 1998 lidar surveys of Assateague Island, MD in response to two large northeasters that produced significant erosion along the Assateague shoreline. Two additional study sites are obtained from 2003 lidar surveys of Hatteras Island, NC in response to erosion caused by Hurricane Isabel. Error statistics generated on these study sites suggest that the models are statistically equivalent in their ability to hindcast dune erosion due to extreme storm events.

Assateague Island is a classic example of a retrograding barrier island, with its recent geological history punctuated by episodes of overwash and breaching. However, in addition to a number of historical inlets, parts of the island owe their origin to relict (pre-historic) channels. The present study was conducted north of the Virginia-Maryland border, focusing on a narrow segment of the island fronting the Green Run Bay. The site lies north of the historical Green Run Inlet that was active until 1880; however, there is no geological evidence of its migration along the island. More than 4 km of high-resolution (250 MHz) ground-penetrating radar (GPR) images, complemented with sediment cores and multi-dating techniques, were used to reconstruct the geological legacy of the Green Run Bay segment of the barrier and to test whether it was the site of an older channel. My findings indicate that a backbarrier paleo-channel still visible within the Green Run Bay corresponds to a large (>380 m wide, 3.0-3.5 m thick) channel cut-and-fill structure revealed in GPR images. The channel fill consists of tangential- to sigmoidal-oblique, southward-dipping reflections downlapping onto channel lag facies, which overlie subhorizontal bay-fill strata. Hummocky reflections in a shore-normal channel transect suggest partial preservation of inlet-related bedforms, believed to be associated with the channel closure. Mollusk shells from the bay fill yield radiocarbon ages of 4630-2400 cal BP (calibrated years before 1950). The paleo-channel facies overlying the bay deposits exhibit a fining-upward sequence, with a mean grain size range of 0.44-2.43 phi. The first set of optical dates indicates that the inlet fill is 660 +/- 70 cal BP (AD 1220-1360). The paleo-channel fill does not extend to the south and therefore is a separate relict feature that predates the historical Green Run Inlet. Based on geophysical and core data, the paleo-tidal prism of the relict channel is 17x10 6 m3. Following the closure of the inlet, a series of beach ridges have developed across the Green Run Bay segment and exhibit signatures of storm erosion in shore-normal GPR profiles. This punctuated barrier progradation took place during the historical period (post-1600), with optical dates of beach ridge and dune generations ranging from AD 1680 to 1920. In addition to geological evidence, dendrochronological records were examined for occurrences of abrupt thinning of tree rings as a proxy for intense environmental stress. Tree samples that exceed 50 years in age (n=7) display an abrupt ring thinning in 1962 that coincides with the Ash Wednesday extra-tropical storm of record. This study demonstrates that the historical stability of the Green Run Bay segment of Assateague Island is likely due to the influx and preservation of substantial sand volume related to a relict tidal inlet. / Geology