Scaling the tiniest element to global impact 

The data collected in these projects across different scales, from the microbial life in soils to large-scale ecosystem reactions, are essential to better understand and model Earth-scale land processes. That’s where ORNL scientist Benjamin Sulman steps in. He is using a suite of biogeochemical and other models to scale these processes and integrate them into the land model of the larger DOE Energy Exascale Earth System Model, or E3SM. The E3SM is an essential capability to understand and predict how the Earth will change in the years ahead under a warming climate. 

Sulman’s work to integrate coastal wetland processes in the E3SM Land Model is the subject of his own DOE Early Career Award, drawing on his expertise in modeling biogeochemical cycles and plant-soil interactions. He’s leading efforts to connect simulations of redox chemistry, tidal hydrology and coastal wetland plant functional types such as salt marsh grasses and mangroves into land model simulations at ecosystem to continental scales. 

“What makes these ecosystems so interesting is that they sit at a lot of interfaces between land and water and between freshwater and saltwater,” Sulman said. “Because of that, they are very dynamic compared to other systems that we might examine. We can see big changes hour-to-hour in the hydrology and biogeochemistry of the coastal system. That’s why they are such hotspots for biogeochemical cycling.”

Coastal areas can store a lot of carbon because they host fast-growing plants, with resulting organic matter buried in sediments — but they can also emit a lot of greenhouse gases such as methane and nitrous oxide that are produced in flooded soils, Sulman added. Tidal fluctuations can input salt or freshwater into the system, so there can be tremendous variability at these interfaces. The scientists found when the ecosystems are more salt-influenced, the sulfate cycle tends to overwhelm other elemental cycles, and that feeds into greenhouse gas production, Sulman said.

Lateral transport of water, nutrients and carbon across wetland landscapes can be an important control on coastal carbon and nutrient balance, and ORNL is leveraging the Advanced Terrestrial Simulator, or ATS, to represent that element. Developed by ORNL and other national laboratories, ATS is a sophisticated model of surface and subsurface flow and transport to better simulate the role of lateral exchanges in coastal systems. Coupling ATS to the E3SM Land Model allows interactions between plants, water flows and subsurface biogeochemistry to be resolved to answer questions that cannot be addressed with simpler models, Sulman said.

“The magnitude of coastal change can be seen in some of the field work ORNL staff is doing today,” he said. “Beth [Herndon] is working on an island in the Mississippi Delta that didn’t exist 50 years ago” as the land shifts. “And if you look at maps of predicted sea level rise, there are a lot of areas along the coast that might not exist 20 to 30 years from now.” By representing these complex coastal processes, you get an improved representation of the carbon balance in the E3SM Land Model, Sulman said. 

Sulman, O’Meara and colleagues reached a milestone recently when they successfully integrated redox reactions and other key coastal ecosystem processes using a biogeochemical model called PFLOTRAN, as detailed in JGR Biogeosciences. They then demonstrated how coastal processes can be connected into the E3SM Land Model, as detailed in the Journal of Advances in Modeling Earth Systems. 

This Oak Ridge National Laboratory news article "Along shifting coastlines, scientists bring the future into focus" was originally found on https://www.ornl.gov/news