No description available.

No description available.

A quantification of the role that barrier island overwash plays in the evolution of Onslow Beach, a barrier island located on Marine Corps Base Camp Lejeune, North Carolina, is presented. Ground-penetrating radar (GPR) and sediment vibracores provide an estimate of the relevant-sand prism above a silty/peat contact underlying the island. The average thickness from the surface, as determined from lidar, to this geologically-defined base, is less than 1 m and equates a total volume of approximately 1.8 ± 1.1 × 106 m3 over the 4.8 km stretch of Onslow Beach from 1 km north of the New River Inlet to Riseley Pier (~ 2 km2). Approximately 39% of the relevant-sand prism (680 ± 215 x 103 m3) is contained within the area of the island currently exhibiting signs of overwash events (i.e., the active overwash complex). Based upon the average cumulative thickness of distinct washover facies within 12 sediment cores (52 cm) and the surface area of the active overwash region, it is estimated that the volume sedimentologically distinct washover deposits equals 199 ± 88 × 103 m3 (approximately 29% of the active overwash complex or 11% of the entire relevant-sand prism). A time series of aerial imagery from 1938 to 2008 details the spatial and temporal trends in migration of both the wet/dry line (a shoreline proxy) and the vegetation line (indicating the landward extent of overwash). Long-term shoreline erosion rates in excess of 3 m/yr occurred over the southern portion of Onslow Beach while the northern portion experienced up to 1.7 m/yr of accretion within the same 80-year time span. Between 1938 and 2008, the vegetation line moved an average of 85 m landward over the length of the entire island and over 450 m in overwash sites at the southern end of the island where shoreline erosion rates are highest. A comparison with long-term shoreline change rates suggests that a simple linear relationship between spatial and temporal variability in shoreline behavior and volume of the relevant-sand prism does not exist. Trends based upon the past 80 years suggest that a positive correlation exists between storm frequency and overwash extent. Furthermore, the region experiencing the highest rates of shoreline erosion and the highest occurrence of overwash does not coincide with the area regularly subject to military training activities. These data suggest that natural forcings (sea level, wind and wave energy, geology, etc.) exert first-order control on the evolution of this barrier island. The ability to quantify and evaluate the relative importance of such forces is paramount to understanding how, and over what timescales, the nearshore environment responds to changes in external forcings (e.g., sea-level rise, storms, etc.) and, in turn, is fundamental to the development of reliable forecasts of shoreline trends and storm susceptibility models.

No description available.

No description available.

Scientists use climate proxies, such as tree rings, to extend the climate record back in time, adding to the growing body of knowledge of past climate change. Tree rings provide a high-resolution proxy of climate. Many of the reconstructed climate records for the western U.S. use ponderosa pine (Pinus ponderosa Douglas ex. C. Lawson), a fire-adapted species that grows in areas prone to frequent fires. Such a disturbance as fire can introduce noise to climate reconstructions by causing growth releases or suppression following a fire event. My objective was to determine whether fire damage causes a quantifiable change in growth patterns of affected trees and whether the affected trees experience the changes in the same way. Increment cores and cross-sections were collected from living and dead ponderosa pine trees in Payette National Forest, central Idaho, U.S.A. One chronology was developed from a stand of ponderosa pine showing no evidence of frequent fire while two chronologies, one from cores collected mostly from trees without visible fire damage and one from cross-sections of fire-scarred trees, snags, and stumps, were developed from a separate cluster of three subsites affected by frequent fire. The mean fire-free interval for all fire subsites was 7.38 years. The mid-1600s to mid-1900s were characterized by nearly continuous fire activity at the fire subsites. The results from superposed epoch analysis (SEA) showed that tree growth is significantly lower than average the year of a fire event. The fire site chronologies showed slightly suppressed growth for 3 years after a fire. Significantly (p < 0.05) below average growth occurred after large fires in the fire site cross-section chronology. The difference chronologies indicated that fire does not cause a systematic change in tree growth and any added signal is comparable to other noise in the chronologies. Analyses using the computer program OUTBREAK showed that some fire years appeared to be followed by growth suppressions while others are not, regardless of fire size. Analyses of the chronologies and the fire history of the subsites indicated that no statistically significant systematic signal is introduced into the tree-growth patterns by fire events.

Three separate but related aspects of sediment allocation in a river/estuarine system were examined. The main purpose was to compare sediment budgets for a series of eleven nested sub-watersheds as a function of watershed size, ranging from 65 to 6900 km2. The approach quantified six budget components: upland erosion; stream bank erosion; colluvial storage; wetland storage; stream channel erosion and storage; and sediment flux at the outlets. Three budgets were developed for each sub-watershed to examine the relative proportions of budget components, budget sensitivity (the influence of individual components on the overall budget), and the uncertainty of budget components. The study area was the rural, forested, low relief York River watershed in southeastern Virginia. The relative proportions of budget components do not change with sub-watershed size. Budgets are more influenced by the tributary system than by the sub-watershed size. The budget is sensitive to most components because they are large in size and are highly variable. The uncertainties of budget components are proportional to the magnitude of the best estimates. Management efforts should focus on locally-derived sediment to improve water quality because little sediment from the upper parts of the watershed reaches the estuary. Sediment loads were needed in the sediment budgets for three estuarine sampling stations. The loads were estimated by separating the gravitational circulation, tidal pumping, and river input components of long-term total suspended solids data. The load for the station closest to the river mouth was somewhat larger than literature values. The contribution to the estuary of the two tributary stations was previously unknown. Tidal pumping, rather than gravitational circulation, is the dominant process moving suspended sediment up the estuary. The potential supply and storage of sediment in wetlands at the watershed level was examined by quantifying the areal extent of wetland type and location in the watershed, and surrounding land use, slope, and soil type. Results showed that these landscape characteristics are unevenly distributed within the York River watershed and its subdivisions. The differences in landscape characteristics between subdivisions suggest that wetland performance and its impact on water quality may vary within a watershed. Separate management approaches may be needed to accommodate these differences.

The present study was focused on developing a shoreline change forecast and wetland response model for Dorchester County, MD, to evaluate the vulnerability of wetlands to shoreline erosion and inundation due to relative sea level rise. The model considers the following forces involved in wetland stability and sustainability: inundation (as a function of topography and sea-level rise), shoreline erosion, vertical accretion and horizontal migration. To predict the long-term risk to nearshore wetlands and the potential habitat zone for wetlands in the next 50 years, shoreline change due to inundation and erosion/accretion was assessed within the frameworks of two-dimensional and three-dimensional analyses. To that end, three different scenarios were taken into account in the shoreline change forecast. The first (conservative) scenario estimated the future shoreline positions based on historic sea-level rates of change and historic erosion/accretion rates. The other two scenarios employed accelerated rates of sea-level rise and accelerated rates of shoreline erosion/accretion in the shoreline forecast. Two different approaches were employed to spatially analyze and combine the outputs of the projections based on inundation and erosion. A Maximum Change approach and a Characterization of the Inundation Forecast were carried out in each scenario. The future location of the shoreline was defined as the wetland-water boundary. The wetland-upland boundary was defined based on current topography (elevations at 2 times the tidal range above mean low water), and the potential wetland habitat was restricted to areas that are not presently developed and/or not behind a shoreline defense structure. The outputs of this model allow identification of potential future wetland habitats where wetland protection and restoration strategies can be directed. This model approach can serve as a prototype for expanded investigations in other coastal habitats.

No description available.

No description available.