Port of San Diego Study Unlocks Treasure Trove of Blue Carbon Information on San Diego Bay’s Eelgrass Beds

SAN DIEGO— The Port of San Diego is releasing the results of its first study on carbon sequestration and storage in eelgrass beds. In 2021, the United States Department of Transportation’s Maritime Administration (MARAD) awarded $150,000 through the Maritime Administration’s Maritime Environment and Technical Assistance (META) program to the Port to assess how much carbon is stored in San Diego Bay’s eelgrass beds and how much carbon eelgrass may continue to sequester into the future.

Eelgrass and other coastal “blue carbon” ecosystems can rapidly capture and store large amounts of carbon. Like all plants, eelgrass absorbs carbon dioxide, which is stored as organic carbon in its plant material and produces oxygen through photosynthesis. When land plants die, their carbon is released into the atmosphere as CO2. Unlike land plants, eelgrass is submerged in water, which prevents the release of CO2. Instead, the organic carbon is sequestered into the sea floor sediments. If left undisturbed, this carbon can remain trapped in eelgrass sediments for thousands of years. Eelgrass habitats cover a small fraction of the area forests do on land, yet they can store carbon at rates 30 to 50 times greater than forests.

The study is funded through MARAD’s Maritime Environmental and Technical Assistance (META) Program, which supports and promotes emerging technologies to improve environmental sustainability in the maritime industry. Carbon sequestration is a crucial area of research that can inform and support ports and the maritime sector in reducing greenhouse gas emissions.

Some key findings from the study, conducted between Oct. 2021 and June 2022, include the following:

  • The bay’s eelgrass beds currently contain 1.7 million metric tons of CO2, equivalent to the same amount of CO2 emitted by more than 370,000 cars annually.
  • Since 1993, the Port and the Navy have conducted bay-wide eelgrass surveys every few years. Presently, San Diego Bay has nearly 2,600 acres of eelgrass, which amounts to 50 percent of all the eelgrass in Southern California and about 17 percent in the state.
  • As much as 73 percent of the bay’s carbon is stored in the sediments of the South Bay.
  • Creating or restoring eelgrass habitat could lead to more carbon storage, potentially supporting the Port’s greenhouse gas emissions reduction efforts.

In addition to storing carbon, eelgrass also helps improve water quality, provides protection from waves that erode shorelines, and is a vital habitat and food source for many animals in and around the bay.

Together, the Port, the Navy, and MARAD have expressed hope to shed more light on this little-studied coastal ecosystem and its potential to support local and regional carbon sequestration efforts. Over the next year, the Port will continue studying the relationship between eelgrass and carbon storage. In addition, through the META program, MARAD has committed $175,000 to a second year of research. A third partner, the U.S. Navy, has joined the effort, allowing the team to study carbon sequestration and storage in the Navy’s eelgrass restoration areas.

This study is an essential component of the Port’s ongoing efforts to protect the resources San Diego Bay provides to the region and to support state and local climate planning efforts. This study also complements the Port’s growing portfolio of nature-based solution projects:

  • Blue Economy Incubator projects – San Diego Bay Aquaculture, ECOncrete, and Sunken Seaweed.
  • Pond 20 – an 85-acre proposed wetland mitigation bank to restore coastal salt marsh habitat with the added benefits of carbon sequestration and ecological enhancement.
  • Native Oyster Living Shoreline Project – created oyster reefs to recruit native oysters, prevent shoreline erosion, and help with carbon sequestration.
  • Restorative Aquaculture Planning – initiating the planning effort to permit seaweed and shellfish farming for restorative benefits, such as water quality improvements, biodiversity enhancement, and carbon sequestration.

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