Legacy blue carbon – long-term storage in seagrass meadows and potential to mitigate climate change

We know that seagrass meadows take up large amounts of carbon in the form of CO2, bind it in their tissue through photosynthesis, and bury and store it in their root systems and the sediment below. However, a lingering question among researchers and practitioners is how resilient this stored blue carbon is, for example when seagrass meadows die-off due to marine heatwaves that are becoming increasingly common with climate change throughout the world. Will this carbon remain “locked” in the sediment, or will it be decomposed and return as CO2 to the atmosphere counteracting the climate benefit of seagrass meadows? Understanding the permanence of carbon storage in these blue carbon systems is critically important for carbon offset credit accounting protocols. Current international protocols require a partial deduction of carbon stored to account for potential carbon loss due to die-off events, but this deduction is highly uncertain.

This project investigates a serious knowledge gap in a widely used nature-based solution to mitigate climate change – uptake and storage of carbon by coastal ecosystems, particularly seagrass meadows. By filling this knowledge gap, the project will move blue carbon research forward and play an important role in upgrading international blue carbon credit accounting protocols. UVA researchers currently working with external partners have co-authored the international protocol for issuing carbon offsets in the voluntary carbon market, adopted by Verra and other carbon offset project validators. Our results will be communicated to them to inform permanence estimates for future offset projects. Duplicate sediment cores will be collected and preserved exclusively for educational use and outreach proposes at UVA and beyond.