By Elena Solohin, Florida International University /NEW ORLEANS, LOUISIANA/
My colleague, Emily, and I, with Florida International University’s Wetland Ecosystems Research Lab, kicked off our 2021 field season with a trip to the Mississippi River Delta to conduct research for NASA’s Delta-X project. We met up with a team of scientists from Louisiana State University and spent two weeks conducting fieldwork across the vast salt meadow, cordgrass marshes and freshwater wetlands of Louisiana’s Atchafalaya and Terrebonne Basins.
More specifically, we set out into the marshes by boat to collect soil cores and biomass (organic matter) from below- and above-ground, and to measure marsh elevation. The data we collected will contribute to Delta-X’s main goal – to project future wetland vulnerability along coastal Louisiana under various scenarios of sea level rise and sediment supply using state-of-the-art remote sensing tools, field observations, and modeling approaches across the two basins.
Our field work was both exciting and challenging. Our boat rides out to the sampling sites were their own adventures especially with the windy, bumpy, and at times, foggy conditions we encountered. When it was time to get out of the boats, we met our next obstacle – navigating the wetlands, dominated by tall cattail, on foot. Walking through the swampy ground is challenging for even the most experienced wetland scientists!
While trying to keep six feet apart from other teams, we took photographs of the wetland vegetation and recorded water levels. The photographs offered a bird’s eye view of the marsh landscapes and vegetation diversity. While we were working, we also marveled at the blue, over-arching sky, the teeming wildlife around us – including a few sets of beady alligator eyes sticking out of the marsh — and above all, the unique beauty of Louisiana’s coastal wetlands.
After each day of hard work, we were glad to have some time to take a break, even if it was in the same marshy area we’d been working. Now, we’re looking forward to processing the samples we collected to generate the data needed to help understand and predict future wetland vulnerability along coastal Louisiana.
By John Mallard and Tamlin Pavelsky, University of North Carolina /NEW ORLEANS, LOUISIANA/
Cruising through a bayou during recent fieldwork in the Mississippi River Delta, our boat driver casually pointed out an alligator and zoomed on by without slowing. After seeing us scramble to get out our phones to take a picture, though, he realized that perhaps these scientists from the piedmont of North Carolina were a bit less used to seeing alligators than the locals of southern Louisiana, and obliged us by circling back around for some pictures.
This alligator is one of the many species of animals and plants that depend on the unique habitat provided by the bayous, marshes, lakes, and rivers of southern Louisiana. Equally dependent on them are people; we rely on them to protect inland towns from tropical storms, support recreational and commercial fishing, and provide transportation networks for global shipping. With this vital role of the region in mind, DeltaX is measuring how water and sediment move through the delta to learn how and why marshes are changing in the area.
Our team, Tamlin Pavelsky and John Mallard from the University of North Carolina, was in the delta in early March to install sensors that measure water level in the marshes, bayous, and lakes. DeltaX is measuring the water surface elevation and extent via aircraft (NASA’s AirSWOT and UAVSAR), which allow us to get measurements across a very large area. Our sensors provide a check on these airborne measurements at the points where we install them. This process of checking our airborne measurements against points on the “ground” is called “validation,” and is a crucial part of using airborne measurements.
Of course, fieldwork had to be modified due to COVID. Prior to fieldwork the team quarantined at home and then formed a pod for the trip. Instead of flying down and buying groceries on site, we rented a car and packed two coolers full of food for the week. We wore masks at all times when we were outside of our accommodations. We self-monitored for COVID symptoms every day. Although these precautions added some time to our work, we were extraordinarily grateful to UNC and to NASA for helping us figure out how to work safely and successfully!
The sensors we installed are pressure transducers. When underwater, they record the pressure of water pushing on a membrane inside the sensor, and then we use that weight to determine the depth of water above them. The sensors are only about the size of a cigar, but they can record tens of thousands of measurements without running out of battery. The sensors we installed in March will stay in the field through Fall, when we’ll return to retrieve them and download the data.
Our work was done from a small motorboat whose flat hull was specially designed to work in shallow water. On a typical day we would meet our hired boat driver at a local boat ramp to put the boat in the water just after breakfast and be back at the boat ramp by 3 p.m. after installing 5-9 sensors. On board, we had about a dozen 10’ lengths of PVC taking up a whole side of the boat, along with our sensors, tools, and food and snacks for the day.
We would navigate to pre-determined locations to install sensors, which were usually on the edge of the water, and the driver would gently run the bow aground to keep us in place. Then we pushed a PVC pipe into the mud as far as we could by hand and finished the job with the post pounder.
We needed to get them deep enough into the mud so that a slit cut in the side of PVC was below the water line and would allow water into the pipe. We tied the sensor to the cap of the pipe using Kevlar cord that is highly resistant to wear, and hung it inside the pipe so that it was below the water surface. At each location we took measurements of the height of the pipe, the length of the cord, and depth of the water so that we could later translate the depth of water measured above the sensor to the actual depth of water at that point. After installing the sensor, we marked the location with a handheld GPS device and moved on to the next site.
On some days we only traveled a few miles and had to take the boat out of the water multiple times to drive to different boat ramps, but on our last day we put in at a single ramp and traveled more than 70 miles across the lakes and bayous of Terrebonne Bay. The weather was sunny, low 70s, and we had lunch on a narrow beach by an inlet separating the Gulf of Mexico from the bay. We watched birds and dolphins fishing for their own lunch of small fish and crustaceans in the inlet. It was a wonderful break at the end of a successful field trip. After a challenging year with so many disruptions of our work, among so many other things, it was such a relief to feel like we’re starting to be able to “get back to work”!
By Amanda Fontenot, Louisiana State University /NEW ORLEANS, LOUISIANA/
Although most of my work happens in the lab, office, or home, field days are some of the most important days of the year for my research. “Going to the field” is when we get to physically visit the wetlands that we spend so much of our time describing, researching, and caring about. Field days can require a lot of effort and time to execute, but they can also be a beautiful time to get out of the office and even have some fun with our colleagues.
I am a graduate student at Louisiana State University (LSU), and I am working towards my Masters of Science in Coastal and Ecological Engineering. I work with Dr. Robert Twilley in the Coastal Systems Ecology Lab at LSU, and my thesis research falls under NASA’s Delta-X Project. In October 2019, Dr. Andre Rovai and I laid a total of sixty-nine feldspar marker horizons at our seven Delta-X field sites in order to measure short-term sediment accretion. This March we traveled back to our markers in the Atchafalaya and Terrebonne basins of coastal Louisiana to measure this accretion.
We made these “markers” by pouring custer feldspar (a fine, white, mineral powder used in ceramics) on top of the soil surface. We use this material because it stays intact and provides a clear indication of when the experiment started. Over time, a soil layer forms on top of the white marker from both plant production and material that is deposited from rivers and the Gulf of Mexico. After placing the marker, our team comes back every 6 months and measures how thick that newly formed soil layer is on top of our marker. We then can divide that number by how many days it has been since we laid the marker, and we end up with a short-term sediment accretion rate. This rate is important in understanding how these wetlands will compete with increasing sea levels and local subsidence that threatens a majority of Louisiana’s coastal wetlands.
Most field days start pretty early in the morning, and this campaign was no exception. Our LSU team (Dr. Andre Rovai, Brandon Wolff, and I) left campus around 4:30 a.m. and headed to the boat launch to put our boat in the water. Since these sites are pretty mucky and we need to be careful to not step on our markers, we also travel with an airboat and our handy dandy airboat operator, Cade. After the boats are in the water, we drive to our sites and get to enjoy a nice sunrise on the water.
Depending on the morning, we usually get to our site around 9:00 or 10:00am and huddle up for a game plan. For this campaign, we needed to complete four tasks at each site: 1) measure accretion on top of our feldspar markers, 2) collect 50cm deep soil cores that help characterize the site, 3) deploy two water level recorders that collect data every 15mins, and 4) measure marsh elevation at varying points using our RTK instrument, which uses satellite-based positioning systems like GPS to estimate the elevation of a point. In the morning, we usually discuss in what order we might finish these tasks and who is in charge of each part of the process.
Most days, I am the one measuring and recording our accretion numbers for the feldspar markers. In order to minimize how much we disturb the soil around and within our feldspar marker, we use what’s called a “cryo-coring” technique – which we have affectionally named collecting “marsh popsicles.” In the field, we push a long, skinny copper pipe into the soil where we previously laid our marker and pump liquid nitrogen into the pipe. Since the liquid nitrogen gets so cold, some of the soil freezes around the pipe and ‘Voilà!’ we pull up our “marsh popsicle.”
On our popsicles, we see our feldspar marker as a white ring around the muddy popsicle. I measure the distance from the top of our popsicle (marsh surface) to that white ring (feldspar marker) with calipers and record it in my field notebook to look at later. Usually by the time we collect all the popsicles we need at the site, we go collect our soil cores and then are ready to eat lunch. We bring our own lunch to enjoy but what’s almost guaranteed is a plethora of light blue Gatorade and Andre’s signature glass bottle of Coke.
After lunch, we continue working on the other tasks for a few hours and try to help out the other field team from Florida International University (FIU) if we finish up before them. When we all finish up our field tasks, we start the long journey home. We pack up our supplies, put samples on ice, change clothes if we got too messy or wet in the field – those boat rides can get really chilly otherwise — and drive the boats back to the launch. At the launch, we get the boats back on the trailer and drive back to LSU, arriving later in the evening.
Depending on the weather, we might go out to another site the next day, meaning a meeting time of 4:30 a.m. back at the school. After we finish at campus, I race home to shower, eat dinner if we haven’t stopped somewhere on the drive back to Baton Rouge, clean my field clothes, and jump in bed to do it all over again the next day. Each team member plays an important role in the field, whether that be holding open bags to store samples, operating our liquid nitrogen tanks, or making sure everyone stays hydrated while we work. Although field days can be quite tiring and stressful, the work that our team accomplishes not only works towards the goals of the Delta-X project but increases the general knowledge of Louisiana’s coastal wetlands and the ecosystem services they provide.