Oregon Sea Grant

Oregon's Blue Carbon Ecosystems: State of the Science

Executive Summary:
Blue carbon refers to the carbon stored and sequestered in the soils, living vegetation, and other biotas in coastal and marine ecosystems. Managing these ecosystems provides an opportunity to mitigate climate change by reducing greenhouse gases (GHGs) emitted into the atmosphere. To help interested stakeholders make sense of this evolving opportunity, The Nature Conservancy in Oregon compiled this document to examine the status of blue carbon science in Oregon and the Pacific Northwest (PNW). Specifically, this report summarizes regionally relevant scientific literature to help readers understand the basics of the blue carbon cycle and GHG mitigation, and the mechanisms of carbon sequestration and storage in Oregon’s coastal and marine ecosystems. With this document, we aim to highlight what is known and what remains unknown concerning coastal and marine blue carbon in Oregon and provide recommendations for managing blue carbon ecosystems as natural climate solutions.

While gaps remain in the evidence base needed to fully assess blue carbon opportunities in Oregon, ongoing efforts continue to fill these gaps. In particular, the work of the PNW Blue Carbon Working Group has significantly contributed to understanding blue carbon ecosystems and dynamics. In some cases, we lacked regionally specific data that would be needed for a robust evaluation of Oregon blue carbon potential. We summarize the existing blue carbon data and limitations in Table 1.

Oregon is among those coastal states with the most plentiful and best-quality blue carbon data. Regionally specific knowledge of carbon dynamics varies depending on the ecosystem type. Blue carbon data gaps for Oregon’s tidal wetlands are rapidly being filled, and the remaining major data gaps related to the PNW’s coastal blue carbon should largely be addressed by the end of 2023. The following additional information needs have been identified:

• Improved habitat mapping of the current and potential extent is needed for more refined estimates of carbon production and sequestration for all wetland types and land uses, in addition to submerged aquatic vegetation (seaweed, eelgrass) to identify potential blue carbon restoration areas at a local scale.
• Understanding the carbon dynamics in coastal and nearshore ecosystems can help clarify the relative role of blue carbon activities in climate mitigation.
• Better salinity mapping can aid in identifying restoration and protection opportunities.
• Climate change, sea level rise, and migration of estuarine and coastal habitats may affect blue carbon resources in the future, but how vulnerable these ecosystems are remains unresolved.
• Regional research is needed to understand carbon dynamics within kelp forest ecosystems and rates of carbon production and sequestration.
• A better understanding is needed of the magnitude of blue carbon benefits provided by marine vertebrates (“fish carbon”) and the methods required to manage them as an oceanic carbon resource.
• Identifying emission reduction opportunities for shellfish and seaweed aquaculture can help clarify how industry and GHG mitigation goals could be harmonized and how production methods could reduce the impact on important co-located blue carbon ecosystems.

While there is still considerable uncertainty about the magnitude of climate mitigation from blue carbon activities, the current science suggests that the following activities are likely to provide some climate mitigation benefits:

• The preservation of existing estuarine and nearshore ecosystems is hugely important for maintaining biodiversity and ecosystem services, including carbon storage.
• Estuary-based conservation projects using existing carbon accounting methodologies are practical and enhance carbon sequestration in tidal wetlands and eelgrass meadows.
• Restoration of tidal flow to diked and drained wetlands generates climate benefits by reducing GHG emissions.
• Site-specific evaluations are necessary to estimate the precise magnitude of the benefit, and a blue carbon calculator is in development as a tool to facilitate these estimations. OREGON’S BLUE CARBON ECOSYSTEMS | THE NATURE CONSERVANCY 2
• Evidence provides reasonable confidence that the restoration of scrub-shrub tidal wetlands provides carbon benefits, which should be emphasized in restoration plans. • Benefits from blue carbon restoration accrue on a decadal scale depending on flux, and practitioners should expect a lag time between restoration and the generation of large carbon gains. Thus, estuary-based projects are needed sooner rather than later to see significant carbon reductions ahead of upcoming climate deadlines.