Re-posted article from UF News by Rachel Wayne, original page here.
Researchers from the University of Florida have found that a delta of a distributary on the Mississippi River created by coastal engineering efforts may have the potential to build long-term sinks of greenhouse gases.
The carbon sequestration potential and guidelines for future engineering and restoration shown in the Wax Lake Delta (WLD) of Louisiana’s Atchafalaya River are described in a paper published today in Nature Geoscience by co-lead authors Michael Shields, postdoc in the Department of Geological Sciences, Thomas Bianchi, Jon and Beverly Thompson Endowed Chair of Geological Sciences, and David Mohrig at the University of Texas at Austin.
The WLD formed naturally after the initial river diversion was engineered, according to the study.
“We discovered that in a system losing land at a rate equivalent to one football field every hour, an engineered river diversion not only built land, but also buried carbon at rates comparable to, or greater than, that of the most efficient terrestrial carbon sinks of similar area,” Shields said.
The land-building accomplished by deltas can reduce atmospheric carbon, and therefore the greenhouse effect, by trapping the carbon in sediment. Careful engineering can divert sediment deposition in the context of other factors, such as storms, runoff and avulsion (when a river abandons its channel). Louisiana’s Coastal Master Plan aims to divert Mississippi River sedimentation into proper receiving basins.
The paper focuses on WLD, a subdelta, that has potential to create a blue carbon habitat (carbon stored in marine and coastal ecosystems). An effect of a diversion built in 1941 to reduce the Atchafalaya’s flooding in a nearby city, it has built about 35 square kilometers of new land. “Engineered river diversions that return sediment to wetlands and bays utilize natural processes to build land and bury carbon in new subdeltas,” explained Shields.
Delta studies must now accommodate a variety of anthropogenic factors, including reservoirs, levees, and subsurface fluid extraction. Delta restoration combines engineering and geological science to encourage continued sedimentation, which “buries” organic carbon, preventing it from returning to the atmosphere.
The researchers sought to measure total carbon storage within the entire delta deposit to account for carbon buried while the delta was still subaqueous (i.e. underwater). Many deltas are threatened by greater subsidence (subterranean sinking and caving) and relative sea-level rise compared to coastlines without deltas. Thus engineering efforts to expand carbon-sequestering habitats must accommodate total carbon sequestration in order to reduce atmospheric carbon.
“When considering the current problems we face with global warming and sea level rise, a greater understanding of how we can stabilize our coastlines and help preserve coastal wetlands is vital for our future,” Bianchi said.
The research was conducted with generous support from Bianchi’s endowed chair by Jon and Beverly Thompson, in collaboration with William F. Kenney of the Land Use and Environmental Change Institute, as well as the Louisiana Universities Marine Consortium.
“Burn and burial,” offers Thomas S. Bianchi, the Jon L. and Beverly A. Thompson Endowed Chair of Geological Sciences, as a central theme of his research. He’s referring to carbon cycling, especially the release of carbon into the atmosphere or its sequestration in flora in “blue carbon” areas, such as wetlands and rivers. Bianchi, sitting in front of a whiteboard with an impressive list of pending publications, talks about his slate of projects, which, like their subject matter, flow into diverse outlets. He’s working on multiple fronts to study “burn and burial” in the face of pollution, dams, and sea level rise.
“Deltas are going to be the first to be inundated by sea level rise.”
“My original focus was not in climate change,” Bianchi says. “Sometimes I wish I had more projects that didn’t connect to it in some way.” It’s a distressingly politicized topic of research (and funding, or lack thereof), although Bianchi is pleased that it’s been “an integrative force for multiple disciplines.” As a biogeochemist, he’s certainly representative of the academic portmanteaus. His passion, however evolved, is palpable as he discusses threats to the cradle of civilization: the fertile delta. “Deltas are going to be the first to be inundated by sea level rise,” says Bianchi. “Some areas are sinking due to natural subsidence and from extraction of oil and natural gas. The Mississippi Delta is experiencing this as sea levels rise while oil and gas reserves are drained.” The loss of deltas is a key topic of Bianchi’s latest book, Deltas and Humans. It’s his first publication for a lay audience and his personal contribution toward expanding the audience for climate science.
Reaching that audience is crucial to bridging the gap between the general public and scientific community, especially on a hot-button topic. Scientists can easily lose debates to those who use “grandstanding and trickery to overwhelm their opponent,” he says. He encourages his peers to train themselves to better express, to the public and the press alike, the dire problem of climate change. There’s plenty of brainpower among the many disciplines already united under the “climate change umbrella,” as he calls it. “Scientists inherited this problem from the Industrial Revolution. We’ve known it longer than the public has,” asserts Bianchi. “Now, scientists must do a better job of getting the word out.”
A Chinese translation of Dr. Bianchi’s book titled Biogeochemistry of Estuaries was recently published, over 10 years since its initial publication. This synthesis covers over three decades of estuarine research and will aid Chinese students and researchers in a field of ever-growing importance.
Salt marshes like this one near St. Augustine, Florida, have stored organic carbon for hundreds to thousands of years in a low oxygen environment.
Coastal environments supporting seagrasses, salt marshes and mangroves are storehouses for vast reserves of organic carbon known as blue carbon. These reservoirs have trapped organic carbon beneath the surface for hundreds to thousands of years in a low oxygen environment.
Unfortunately, coastal zones are changing due to rising sea levels and human encroachment. The combination of erosion and habitat destruction is allowing the trapped blue carbon to mix with seawater. Organisms in seawater are consuming the organic carbon and releasing carbon dioxide into the atmosphere.
“There’s growing interest in blue carbon habitats, because they perform a natural and valuable service by sequestering CO2,” says Thomas Bianchi, Jon and Beverly Thompson Endowed Chair of Geological Sciences at the University of Florida. “Coastal plants use the CO2 to grow through photosynthesis, but they also store it for long periods in the soils and sediments they live in. That’s unique, because other plant habitats cycle CO2 out of their soils into the atmosphere much quicker.”
The research team includes Co-PIs Andrew Ogram and Todd Osborne, postdoctoral associate Ana Arellano, and graduate students Elise Morrison and Derrick Vaughn, all with the University of Florida; Co-PI Nicholas Ward, a scientist at the Pacific Northwest National Laboratory; and Yina Liu, an EMSL postdoctoral researcher. A self-funded study, support comes from the Thompson endowment and the University of Florida.
“We’re interested in studying what happens when you take this big carbon sink in coastal soils and sediments, and you start carving at it with sea level rise and wave erosion,” says Bianchi. “What controls how quickly that carbon gets converted back into CO2?”
Priming is one of the factors affecting the speed stored carbon becomes CO2. For example, microbes have difficulty breaking down straw. Mixing straw with alfalfa accelerates the decomposition process. The microbes quickly eat the alfalfa, but they also break down the straw. The presence of more digestible material primes the straw to be broken down.
Scientists have studied the priming effect in soils, but few studies have investigated priming in coastal systems. In this study, priming is the mixing of decayed higher plant material (plants with rooted systems) with coastal algae to allow microbes to break it down faster.
“We hypothesized that the breakdown of the stored blue carbon would be much faster in the presence of algae than in the absence of it,” says Bianchi.
Bianchi’s team tested the hypothesis with a series of experiments performed at the University of Florida Whitney Laboratory for Marine Bioscience using seawater, an algae mixture, and coastal peat from Florida wetlands in four treatments – (1) seawater control, (2) seawater and algae mixture, (3) seawater and peat, and (4) seawater, algae mixture and peat. They measured the amount of CO2 produced over time by the four treatments. The team used isotopes as chemical markers to track the source of the CO2 molecules. Samples from these experiments were submitted to EMSL and the DOE JGI for high-resolution measurements of organic carbon composition and microbial genetic responses.
“Our preliminary data supports our hypothesis,” says Bianchi. “In the presence of algae you get more blue carbon peat being converted to CO2.”
The priming effect could be more dramatic as oceans become greener with algae due to pollution from fertilizers and other farm runoff.
Getting to know microbes
The project is also using EMSL and DOE JGI capabilities to study microbial communities that convert peat into CO2. They want to know how communities change in the presence and absence of algae. They are also interested in how the microbes decompose peat, including what enzymes they use. The team is using EMSL’s mass spectrometry and nuclear magnetic resonance expertise and capabilities for this portion of the research.
“Being a FICUS project gives us a fantastic opportunity to use two of the best research facilities in the world,” says Bianchi. “Working with EMSL and (DOE) JGI will help us understand how priming works, because we really don’t know all the details about it.”
Bianchi says the study’s findings could improve climate models as the global models scale down. Sophisticated climate models are starting to account for regional effects. The findings could be added to a regional-based model that includes a conversion of land lost to CO2 with priming as an enhancement factor.
“There’s a bigger story,” says Bianchi. “A greener coastal ocean and a destabilized coastal environment due to sea level rise and land use changes are causing a rapid turnover of stored carbon that’s hundreds and thousands of years old being converted into CO2 in part through the priming process.”
Learn more about the current FICUS call for letters of intent, and how you can use the expertise and capabilities at EMSL and the DOE JGI to improve your research.
Angelica Ares, an undergraduate Biology major working on her research project, within the UF Center for Undergraduate Research, in Dr. Bianchi’s lab was selected to present her research at the Gulf Coast Undergraduate Symposium in October 2016 at Rice University Houston, Texas. She and about 100 other students were selected from universities around the country to make a 15 minute oral presentation on results from their research. Angelica is working under the direction if Bianchi and one of his Ph.D students Xiaowen Zhang, on this project which is funded by the National Science Foundation. This work basically involves the relationship between carbon cycling and the ecohydrology of different vegetational habitats in Big Cyrpress Swamp, in southern Florida. Bianchi is co-PI along with Jon Martin, also in Geological Sciences at UF on this project, which is lead by Matthew Cohen in the UF School of Forest Resources and Conservation.