Justin, Tony and Matt ready to get into the water at Onslow Beach.
The southwestern half of Onslow Beach, NC is starved of sand. Using a side-scan sonar, we imaged peat and organic-rich sediment at the seafloor just seaward from where the waves start to break. Offshore from that, Miocene rock is imaged at the seafloor. It is difficult, at least for us, to get a true sense of what the seafloor looks like from these geophysical data (scale, rock type, relief, etc.). To gain perspective, we decided to SCUBA dive and collect a video of the seafloor from the shoreline to about 300 m offshore. Visibility nearshore was very low because that organic-rich mud was eroding and being suspended in the water column. Once we reached about 200 m from shore, visibility improved and we could clearly see rock outcropping at the seafloor (Belgrade Formation). That rock is shown in the video below, taken at a depth of about 7 m (23 feet).
Onslow Beach, NC during a sea-level anomaly in 2009.
Sea-level anomalies are periods greater than 2 weeks when the water level at the beach is high. They are not necessarily related to storm surge or sea-level rise, rather they are forced by changes in ocean currents. On the US East Coast, slowing of the Gulf Stream or meteorological phenomena, like northeasterly winds or pressure changes, can pile water up against the shore and cause a sea-level anomaly. They impact large stretches of coastline (e.g. Massachusetts to Florida) and occur every year, but some years they are more frequent. Ethan Theuerkauf recently published a paper in Geophysical Research Letters that presents the first direct measures of the effects of sea-level anomalies on beaches. He shows that a year with frequent sea-level anomalies can cause as much beach erosion as a year with a hurricane. Compare Onslow Beach, NC during a sea-level anomaly, above, with Hurricane Arthur (July 3, 2014), below. The hurricane made landfall at night, but you can still make out overwash (the camera is pointed landward across a washover fan).
We completed the restoration project after constructing reefs with 3,500 bushels of shell and planting 2,000 bundles of marsh grass. It took 2.5 days with 15 people working, including students, technicians, summer researchers, and faculty.
I’m really pleased with the end product. Now it’s a waiting game to see if oysters will settle on the cultch and the marsh plants will take hold. It is basically out of our hands now. In a few weeks we will revisit the site and survey the reefs and shoreline. Those data will served as a baseline from which to measure reef growth from. Emily Woodward collected the time-lapse video of reef construction (shown here), using a GoPro camera.
The project involves planting a saltmarsh and an oyster reef. The first step was applying for a CAMA permit because we need to distribute oyster-shell cultch near the shoreline. We anticipate that oyster larvae will settle on the shell and a reef will be created by the end of the summer. We need a reef in the nearshore because IMS is adjacent to the Intracoastal Waterway and the reef should protect the saltmarsh from boat wakes. The CAMA permit required us to jump through many hoops and as I write this it is still not signed (hopefully in a few hours). The new reef and saltmarsh should promote expansion of the adjacent seagrass meadow, provide important fish habitat, clean the water, and sequester carbon. Below, is a figure showing our final design.
Why does the IMS shoreline need to be restored? Because…
1) It currently looks like this:
2) We are supposed to be stewards of the coast and we are not setting a good example with our rip-rap revetment.
3) To improve fish habitat and sequester carbon. The project is funded by the University of North Carolina at Chapel Hill Energy Services Department. UNC has pledged to reach carbon neutrality by mid-century. They will take credit for carbon offsets associated with the saltmarsh and oyster reefs we are planting. This is another example of IMS faculty working together. The effort is led by the Rodriguez, Fodrie, and Piehler labs. Stay tuned for project updates.
A core through a reef constructed in 1997
Inter-tidal reefs grow so quickly, they should be able to keep up with any future rate of sea-level rise. That’s good news because in the lower parts of estuaries oyster reefs need to maintain an intertidal elevation to thrive and the areal extent of oyster reefs is only a fraction of what it used to be before over harvesting. That rapid rate of growth is not sustainable because if it were it wouldn’t take long for a reef to be high and dry and oysters must be underwater at least half of the time. As you might expect, different parts of the reef grow at different rates. We have a new paper published in Nature Climate Change that presents the first reef-scale measures of growth. Our work shows that oyster-reef restoration has a high probability of success in inter-tidal areas. If inter-tidal reefs are restored close to marsh shorelines one could end up with a reef that will help protect the shoreline from erosion, filter water, provide fish habitat, and be able to keep up with sea-level rise. No rock sill can do those things.
My favorite part about the study is that it’s interdisciplinary (interface between ecology and geology) . There are lots of coauthors and I know the study would not have been completed without everyone’s contributions. If you keep visiting my site, in the future you will see more interdisciplinary oyster- reef studies, like their roll in the carbon and nitrogen cycles, comparing growth over multiple time scales, and quantifying the relationship between aerial exposure and growth rate.
We measured reef growth from high-resolution digital elevation models.
Reefs were constructed as 3 x 5 x 0.15 m boxes.
Why is Ethan so happy? Well, he just published a new paper in Earth Surface Processes and Landforms entitled, “Evaluating proxies for estimating subaerial beach volume change across increasing time scales and various morphologies“. In the paper, Ethan critically evaluates proxies, such as changes in beach profiles and shoreline positions, which are commonly used in management and research for estimating changes in subaerial beach volume. He used terrestrial laser scanning data to create multiple high-resolution topography maps of beaches with variable morphology over a period of 3.5 years. Those maps were then used to compare the various volume-change proxies. This work is important because management decisions and research results may be adversely influenced by inaccurate depictions of beach volume change that were based on a proxy that is not well suited to that particular beach morphology or time frame of interest. Check out his paper online and don’t forget to look at supplemental information where all of the maps are displayed.
In the past we have relied on aerial photography when measuring the morphology of washover fans. These fans are constantly changing shape, but we aren’t able to document these changes because images taken from a plane are only collected every couple of years. To remedy the problem, we’ve attached a GoPro to a remote-controlled quadcopter that we use to fly over the fans. With this technology, we’ve managed to capture some awesome, high-quality aerial images of the fan.
The benefit of using the quadcopter is not only limited to measuring washover fans – we’ve also started flying over man-made oyster reefs in Middle Marsh, NC. The images and videos taken with the GoPro will help us assess the growth of the reefs.
Bayhead deltas are located where rivers flow into estuaries. They have broad low-elevation plains that are sensitive to small increases in the rate of sea-level rise. In the past, when sea level was rising at a rate of 1 m per 100 years, bayhead deltas across the Northern Gulf of Mexico experienced a phase of rapid landward retreat. Subsequently, those bayhead deltas stabilized and Alex Simms (UC Santa Barbara) and I are interested in better understanding controls on bay-head delta stabilization following rapid retreat. We recently published a paper in Geophysical Research Letters that shows bayhead deltas stabilize at tributary junctions as they are moving landward in response to sea-level rise. These results highlight the shortcomings of models that predict the impacts of sea-level rise by simply flooding topography (i.e. bathtub or passive-inundation models). One of those passive-inundation models is being served by NOAA. Play with the NOAA model online and then read our paper.
Ethan and Justin created SciREN, the Scientific Research and Education Network, to establish a forum through which scientists can efficiently provide teachers scientific resources for the classroom. The first event was held at the Pine Knoll Shores Aquarium in April 2013. To get the word out and inspire others to host SciREN events at different venues across the country, Ethan and Justin wrote an article for EOS, Transactions of the American Geophysical Union, which was published on Feb 4. Check it out and remember, it’s not enough to publish results in scientific journals; new concepts need to be disseminated to the entire community, including K-12.