We’re contemplating how to sample the barrier with all of that shrubbery in the way.
For the past few years we have been working on compiling a data set of the age and landward extent of ancient washover fans on a Barrier Island in North Carolina. An ancient washover fan is identified as a sand bed sandwiched between two saltmarsh units. We had one last washover fan to map and decided to use an Edelman Auger instead of vibracoring because we knew that this part of the beach was difficult to access. The vibracoring rig is heavy, bulky, and requires a lot of space to use so we thought a hand auger would be the way to go; big mistake.
We first tried it on the backshore, and everything was going well until we hit the water table and the hole kept filling in. We are supposed to be able to sample below the water table with this tool, but it is very difficult to pull the tool out of the ground after the hole collapses. One thing I learned is that it’s time for Ethan and me to hit the gym.
Each pile represents a 25-cm sample interval. We sampled to a depth of 2 m. Wish we had brought the vibracore.
We tried to access the middle of the island, but the vegetation was too dense. We crawled into the thicket, and in addition to the lack of space, it smelled like something had died nearby and was in the middle of decomposing. We ended up hiking around the back of the thicket to collect our samples and managed to penetrate down to about 3 m, which was deep enough to sample the entire island. The Edelman Auger might work well in other environments, but it is not the right tool for sampling a barrier island, unless you are only interested in the upper 1 m of stratigraphy.
Ethan confirming the smell of death and the lack of room to collect samples in the thicket.
Collecting samples on the back side of the thicket in the phragmites marsh. We spent all day basically digging holes.
The Ocean 180 video challenge is to create a video abstract, which is a short (180 second) piece summarizing the results of a recently-published, peer-reviewed study on any ocean-science related topic. Justin Ridge entered and chose a recent GRL paper on sea-level anomalies and beach erosion as the topic. Who better to star in the video than the author of the paper, Ethan Theuerkauf? The target audience is middle school students. Justin did a great job, but unfortunately didn’t progress to the next round. Take a look at his video, then watch the Ocean 180 Video Challenge finalists. Justin’s going to try again next year and focus on a different topic, possibly some of his work on oyster reefs.
Justin Ridge found out last week that he is one of six winners, nation wide, for excellence in coastal and marine graduate study. “Justin Ridge, a Ph.D. student at the University of North Carolina at Chapel Hill, is using innovative techniques to assist in restoration efforts of oyster reef communities. He also co-founded a unique educational program for K-12 teachers, where fellow students and faculty share their research with the teachers, who in turn, bring that information into their classrooms.” Check out information on all of the winners at the NOAA website, and more information on North Carolina winners at NC Sea Grant. We are all very proud of Justin at UNC-IMS! Keep up the good work.
Collecting a vibracore from Onslow Beach, NC.
There are many reasons to collect cores from a beach. One of the most interesting is to look back in time and see what environments used to be where the beach is today. The core is like a time machine, or better yet, a history book. You just have to learn the language geology. The cores we took today tell us that there used to be a saltmarsh where the beach is, because below the beach sand we sampled old marsh plants. Before the saltmarsh, an estuary occupied the area because we sampled gray mud with an oyster reef below the marsh sediment. This stacking pattern of different environments is evidence that sea level has been rising in the area of Onslow Beach, NC. Earth’s history is beneath our feet and collecting cores is one way of exposing it.
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.