Ethan J. Theuerkauf

Sea level anomalies exacerbate beach erosion

Sea level anomalies are intra-seasonal increases in water level forced by meteorological and oceanographic processes unrelated to storms. The effects of sea level anomalies on beach morphology are unknown but important to constrain because these events have been recognized over large stretches of continental margins. Here, we present beach erosion measurements along Onslow Beach, a barrier island on the U.S. East Coast, in response to a year with frequent sea level anomalies and no major storms. The anomalies enabled extensive erosion, which was similar and in most places greater than the erosion that occurred during a year with a hurricane. These results highlight the importance of sea level anomalies in facilitating coastal erosion and advocate for their inclusion in beach-erosion models and management plans. Sea level anomalies amplify the erosive effects of accelerated sea level rise and changes in storminess associated with global climate change.

Impacts of Transect Location and Variations in Along-Beach Morphology on Measuring Volume Change

Abstract THEUERKAUF, E.J. and RODRIGUEZ, A.B., 2012. Impacts of transect location and variations in along-beach morphology on measuring volume change. Real Time Kinematic–GPS profile surveys are currently the most common method used by engineers and researchers for monitoring beach erosion. This study assesses the accuracy of volumetric-change measurements based on profile surveys at various beach morphologies along Onslow Beach, North Carolina. High-resolution digital elevation models (DEMs) were created from topographic data collected using a three-dimensional terrestrial laser scanner at six ∼150-m-long focus sites at annual, seasonal, and storm time intervals. Profiles were extracted from the DEMs every 0.5 m along the beach, a distance equal to the grid size, and each profile was independently used to measure volumetric change at each site. Along-beach variability in the measurements of volumetric change was analyzed to test the assumption that one transect can be used to determine volumetric change for a ∼150-m stretch of beach. Results show that the accuracy of profile-based volumetric change decreases as along-beach morphologic variability increases. At sites with beach cusps, beach nourishment, and pockets of anomalous erosion and/or accretion, less than 5% of the ∼300 transects accurately measure volumetric change to within ±10% of the true volumetric change. At the site with the lowest along-beach morphologic variability, that number only increased to 35% of the ∼300 transects. Three-dimensional surveys or closely spaced beach profiles should be employed at morphologically variable, and/or recently nourished or engineered, beaches to accurately quantify erosion and accretion over short timescales.

Abrupt Increase in Washover Deposition Along a Transgressive Barrier Island During the Late Nineteenth Century Acceleration in Sea-Level Rise

Determining the magnitude of barrier-island geomorphologic change and response time to an increase in the rate of sea-level rise is important because sea-level rise is accelerating, many barriers islands are urban centers, and barriers buffer mainland shorelines and estuaries from ocean processes, especially during storms. Here, we show that Onslow Beach, NC, a sediment-starved transgressive barrier island located along a cuspate shoreline, had an immediate increase in apparent frequency and landward extent of washover deposition during the late nineteenth century increase in the rate of relative sea-level rise. The evolution of the barrier at millennial to decadal time scales was reconstructed from sediment cores, radiocarbon dates, and remote sensing. Those data show that the oldest washover deposit preserved in the stratigraphy of the island is approximately AD 722 and at that time the island was seaward of its present location and an open-water lagoon separated it from the mainland. Barrier-island transgression progressed mainly through overwash processes and saltmarsh replaced the lagoon by AD 1500. During the nineteenth century, the number and landward extent of washover deposits increased abruptly along the island concurrently with a threefold increase in the rate of relative sea-level rise. This was not a period of increased storminess in the Atlantic. Rather, the increase in number and landward extent of washover deposits is interpreted to have been caused by an increase in the rate of island transgression. The increase in the rate of relative sea-level rise, and possibly other contemporaneous mechanisms such as changes in wave climate, likely caused island narrowing through landward movement of the shoreline, lowered the elevation of the island principally through erosion of the dunes and made the island more vulnerable to overwash. These data suggest that transgressive barriers, especially those at the center of a coastal embayment, are extremely sensitive to increases in water level, which cause an abrupt decrease in resistance to overwash. The response of other barrier islands to accelerating sea-level rise may well be similarly rapid, but the degree of geomorphic change will vary depending on island morphology, rates of sediment supply, and physical processes.

Maximizing oyster-reef growth supports green infrastructure with accelerating sea-level rise.

Within intertidal communities, aerial exposure (emergence during the tidal cycle) generates strong vertical zonation patterns with distinct growth boundaries regulated by physiological and external stressors. Forecasted accelerations in sea-level rise (SLR) will shift the position of these critical boundaries in ways we cannot yet fully predict, but landward migration will be impaired by coastal development, amplifying the importance of foundation species’ ability to maintain their position relative to rising sea levels via vertical growth. Here we show the effects of emergence on vertical oyster-reef growth by determining the conditions at which intertidal reefs thrive and the sharp boundaries where reefs fail, which shift with changes in sea level. We found that oyster reef growth is unimodal relative to emergence, with greatest growth rates occurring between 20–40% exposure, and zero-growth boundaries at 10% and 55% exposures. Notably, along the lower growth boundary (10%), increased rates of SLR would outpace reef accretion, thereby reducing the depth range of substrate suitable for reef maintenance and formation, and exacerbating habitat loss along developed shorelines. Our results identify where, within intertidal areas, constructed or natural oyster reefs will persist and function best as green infrastructure to enhance coastal resiliency under conditions of accelerating SLR.

Density-dependent role of an invasive marsh grass, Phragmites australis, on ecosystem service provision

Invasive species can positively, neutrally, or negatively affect the provision of ecosystem services. The direction and magnitude of this effect can be a function of the invaders’ density and the service(s) of interest. We assessed the density-dependent effect of an invasive marsh grass, Phragmites australis, on three ecosystem services (plant diversity and community structure, shoreline stabilization, and carbon storage) in two oligohaline marshes within the North Carolina Coastal Reserve and National Estuarine Research Reserve System (NCNERR), USA. Plant species richness was equivalent among low, medium and high Phragmites density plots, and overall plant community composition did not vary significantly by Phragmites density. Shoreline change was most negative (landward retreat) where Phragmites density was highest (-0.40 ± 0.19 m yr-1 vs. -0.31 ± 0.10 for low density Phragmites) in the high energy marsh of Kitty Hawk Woods Reserve and most positive (soundward advance) where Phragmites density was highest (0.19 ± 0.05 m yr-1 vs. 0.12 ± 0.07 for low density Phragmites) in the lower energy marsh of Currituck Banks Reserve, although there was no significant effect of Phragmites density on shoreline change. In Currituck Banks, mean soil carbon content was approximately equivalent in cores extracted from low and high Phragmites density plots (23.23 ± 2.0 kg C m-3 vs. 22.81 ± 3.8). In Kitty Hawk Woods, mean soil carbon content was greater in low Phragmites density plots (36.63 ± 10.22 kg C m-3) than those with medium (13.99 ± 1.23 kg C m-3) or high density (21.61 ± 4.53 kg C m-3), but differences were not significant. These findings suggest an overall neutral density-dependent effect of Phragmites on three ecosystem services within two oligohaline marshes in different environmental settings within a protected reserve system. Moreover, the conceptual framework of this study can broadly inform an ecosystem services-based approach to invasive species management.

Placing barrier‐island transgression in a blue‐carbon context

Backbarrier saltmarshes are considered carbon sinks; however, barrier island transgression and the associated processes of erosion and overwash are typically not included in coastal carbon budgets. Here, we present a carbon-budget model for transgressive barrier islands that includes a dynamic carbon-storage term, driven by backbarrier-marsh width, and a carbon-export term, driven by ocean and backbarrier shoreline erosion. To examine the impacts of storms, human disturbances and the backbarrier setting of a transgressive barrier island on carbon budgets and reservoirs, the model was applied to sites at Core Banks and Onslow Beach, NC, USA. Results show that shoreline erosion and burial of backbarrier marsh from washover deposition and dredge-spoil disposal temporarily transitioned each site into a net exporter (source) of carbon. The magnitude of the carbon reservoir was linked to the backbarrier setting of an island. Carbon reservoirs of study sites separated from the mainland by only backbarrier marsh (no lagoon) decreased for over a decade because carbon storage could not keep pace with erosion. With progressive narrowing of the backbarrier marsh, these barriers will begin to function more persistently as carbon sources until the reservoir is depleted at the point where the barrier welds with the mainland. Undeveloped barrier islands with wide lagoons are carbon sources briefly during erosive periods; however, at century time scales are net carbon importers (sinks) because new marsh habitat can form during barrier rollover. Human development on backbarrier saltmarsh serves to reduce the carbon storage capacity and can hasten the transition of an island from a sink to a source.

Researchers bring local science into classrooms

The need to communicate scientific research beyond academia is increasing concurrently with a growing emphasis on science, technology, engineering, and mathematics (STEM) in K–12 education [Breiner et al., 2012]. Connecting scientists with K–12 educators who will share research with students in their classrooms is an effective method for broadening the audience for scientific research. However, establishing connections with teachers can be difficult, as there are few networking opportunities between these two groups without one directly contacting the other.