Quantifying Carbon Sequestration in Restored Seagrass Meadows for Climate Mitigation

Seagrasses, vital marine flowering plants, cover less than 0.2% of the ocean floor yet play a crucial role in carbon sequestration, contributing up to 18% of annual ocean carbon burial. Their decline due to human impacts, such as rising temperatures, nutrient runoff, and invasive species, threatens this ecosystem service, with California losing approximately 35% of its seagrass cover since 1980. This research aims to address critical knowledge gaps regarding the carbon storage capacity and sediment dynamics in restored versus natural seagrass meadows, focusing on their effectiveness as a nature-based approach to meet the mitigation goals outlined in the Paris Climate Agreement. The study is centered on three primary objectives, developed in collaboration with two U.S. National Marine Sanctuaries, and focuses on California’s dominant seagrass species, Zostera marina (eelgrass): 1) assessing short-term sediment accumulation and erosion rates before and after restoration; 2) comparing carbon stocks in recently restored meadows with those in natural meadows; and 3) investigating the contributions of allochthonous carbon from adjacent ecosystems. We hypothesize that restoration efforts will enhance sedimentation rates relative to control unvegetated sites, and that restored meadows will initially sequester carbon at lower rates than natural meadows, eventually achieving parity within 2–3 years. To achieve these objectives, we have employed field experiments and laboratory analyses. Specifically, 24 subsurface sediment plates were installed in Central California to monitor sediment changes, and sediment cores were collected to analyze total organic matter and grain size. Stable isotope analyses will help differentiate mixed sources of carbon, providing insights into contributions from seagrass, salt marshes, and terrestrial inputs—a critical science need identified by carbon credit methodologies and greenhouse gas inventories. Preliminary results show short-term accumulation of sediments composed of approximately 7.72% total organic matter. By elucidating the carbon dynamics associated with seagrass restoration, this research contributes to understanding the potential of nature-based solutions in climate mitigation and adaptation. It also emphasizes the importance of community engagement in formulating research questions, ensuring that the work addresses the needs of local stakeholders. Ultimately, our findings will inform strategies for enhancing the resilience of coastal ecosystems and communities in the face of ongoing climate change.