Sea Level Rise Is a Double-Edged Sword for Coastal Carbon Sequestration

The Science

Coasts are resilient to climate change and can continue to store increasing amounts of carbon as sea level rises. To do this, marshes expand into lands that were previously coastal forest and maintain their elevation. However, if sea level rise rates are too great, the marsh is unable to keep pace, and the entire marsh system collapses, resulting in lower coastal carbon storage. This study demonstrates that as sea level rises, the coastal landscape changes where most of its carbon is stored from stable forest trees to more vulnerable marsh soils.

The Impact

Findings have direct implications for blue carbon projects globally. This research demonstrates that allochthonous carbon (i.e., carbon not produced by local vegetation) could be up to 50% of the total marsh soil carbon. Blue carbon policy only counts locally produced carbon in offsetting programs.

Additionally, due to the changing location of carbon in the coastal landscape, perturbations in the system (e.g., storms) could have larger consequences for carbon storage in the coastal zone.

Summary

The world’s coasts are responding rapidly to climate change, but most models do not incorporate how adjacent ecosystems interact and how this impacts ecosystem function. In this study, researchers coupled geomorphic processes and carbon dynamics in a numerical model that spans the bay-marsh-forest transect to understand the entire coastal zone’s future. Across the coastal zone, carbon storage increases with sea level rise. As the coast continues to store more carbon, stable carbon is lost from the coastal forest and compensated by gains in marsh soils. While this shift increases carbon sequestration and potential for mitigation of climate change, carbon is placed in a more vulnerable place in the landscape. Once extreme rates of sea level rise are achieved, the coastal system collapses.

Through this innovative modeling framework, researchers also were able to track carbon across landscapes. Results show that connectivity of carbon between coastal ecosystems is critical for maintaining the coastal carbon sink. Up to half of the carbon stored in marshes may be carbon that was produced elsewhere and transported to marshes. Without connectivity, the marsh has limited capacity to keep up with sea level rise and collapses under lower rates of sea level rise.

Principal Investigator

Matthew Kirwan
Virginia Institute of Marine Science
[email protected]

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This work was supported by the National Science Foundation (NSF) Faculty Early Career Development (CAREER) Program (GLD 1654374). Additional support was provided by the Biological and Environmental Research (BER) program within the U.S. Department of Energy’s Office of Science under grant nos. DE-SC0014413 and DE-SC0019110.

Related Links

• Behind the Paper

References