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Summer 2023: Net Zero

Blue Carbon as a Means to Reaching Net Zero

Catherine M Janasie


  • Discusses blue carbon as a means to achieve net-zero emissions
  • Considers the nuanced definitions of blue carbon
  • Examines the complexities and challenges of blue carbon credits
Blue Carbon as a Means to Reaching Net Zero
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Blue carbon is receiving more attention as a nature-based solution in coastal and marine ecosystems to reduce the impacts of climate change. Blue carbon ecosystems like tidal marshes, mangrove forests, and seagrass meadows provide many resilience benefits but are also one of the most threatened ecosystems on earth. Generating carbon credits by protecting blue carbon ecosystems is currently just a small slice of international carbon markets, but it has the potential to grow exponentially. All blue carbon projects have similar barriers and require similar characteristics to ensure they are creating viable carbon credits. However, the framework for coastal projects, such as mangrove restoration, is significantly more developed than offshore, marine projects, such as seaweed cultivation. This article would provide an overview of blue carbon as a method to achieve net-zero emissions, and, in particular, the potential of offshore seaweed projects.

What Is Blue Carbon?

Blue carbon is often simply defined as carbon captured and sequestered by marine ecosystems. However, depending on the context, definitions for blue carbon may be more detailed or nuanced. For instance, a 2022 report released by a global coalition of ocean leaders including The Nature Conservancy defined blue carbon as “nature-based solutions in coastal and marine ecosystems where anthropogenic threats can be mitigated to measurably reduce climate change impacts using robust and accepted methodologies.” Conservation Int’l et al., High Quality Blue Carbon Principles and Guidance: A Triple-Benefit Investment for People, Nature, and Climate (2022). In comparison, a May 2023 Blue Carbon Law Symposium, organized by the S.C. Sea Grant Consortium, focused on coastal areas (as opposed to offshore, marine areas) and defines blue carbon for the purpose of the meeting as natural marine and coastal areas that can capture and store atmospheric carbon into natural biomass; currently defined coastal blue carbon systems are mangroves, salt marshes, and seagrass.

Coastal areas like mangroves, salt marshes, and seagrass beds have the ability to sequester and store large amounts of carbon, but also provide additional ecosystem services such as protecting against flooding, cleaning water, and providing vital habitats. These areas are also disappearing at an alarming rate. Therefore, protecting coastal areas as part of a blue carbon market has a dual benefit of preserving these important coastal ecosystems while also sequestering carbon. The ocean itself is also a compelling carbon sink. While the ocean currently absorbs greater than a quarter of man-made carbon emissions, potential offshore projects including seaweed conservation and farming could increase the oceans’ capacity to absorb carbon. Korey Silverman-Roati, Romany M. Webb & Michael B. Gerrard, Removing Carbon Dioxide Through Seaweed Cultivation: Legal Challenges and Opportunities (Sept. 2021).

The High-Quality Blue Carbon report identifies five principles for developing high-quality blue carbon credits and projects while also improving the resilience of ecosystems and coastal communities. These principles include: (1) safeguarding nature in order to “conserve our planet’s remaining intact resources, design projects in accordance with science-based ecological protocols, and do no harm”; (2) empowering people by implementing “social safeguards to protect and enhance community member rights, knowledge, and leadership and foster equitable access to the global carbon market”; (3) employing “the best information, interventions, and carbon accounting practices”; (4) operating “locally and contextually,” including in regards to policy and governance structures; and (5) mobilizing “high-integrity capital,” including promoting “fair and transparent pricing and compensation.” Conservation Int’l et al., supra.

Other important factors for blue carbon projects, similar to other carbon market projects, are that the projects (1) must have permanence and durability in order to generate credits and achieve carbon sequestration; (2) cannot increase emissions outside of the project, known as leakage; and (3) must produce a benefit that would not occur without the projects, known as additionality.

Sequestering Carbon with Seaweed

Seaweed has been characterized as a “charismatic carbon,” meaning that it “can offer co-benefits, in addition to carbon sequestration.” Halley E. Froehlich et al., Blue Growth Potential to Mitigate Climate Change Through Seaweed Offsetting, 29 Current Biology 3087 (2019). Seaweed production has been identified as a means to reduce hypoxia, eutrophication, and ocean acidification. Seaweed farms can also increase biodiversity by increasing habitat and protect coasts from storms “by attenuating wave energy.” UN Global Compact, Seaweed as a Nature-Based Climate Solution Vision Statement, at 12 (2021). Farmed seaweed can also be used in a variety of products to help accelerate decarbonization, including biofuels, low-carbon food, fertilizers, fabrics, and animal feed to reduce the methane emissions from ruminant livestock. Id. at 9.

Seaweed fragments detach from plants during their growth cycle, sink, and sequester carbon on the sediments beneath marine waters.

Seaweed can sequester carbon in several different ways. Natural kelp forests have always sequestered carbon. Additionally, seaweed fragments detach from plants during their growth cycle, sink, and sequester carbon on the sediments beneath marine waters. Fragments from seaweed cultivation for other intended uses, such as for food, biofuels, or fertilizers, can similarly sink and sequester carbon. Finally, projects can grow seaweed for the primary purpose of sequestering carbon by sinking the seaweed in the deep ocean. Id. at 7. Thus, seaweed blue carbon projects can refer to either restoring natural seaweed beds or cultivating seaweed for the sole purpose of sequestering carbon. Both of these projects could potentially generate carbon credits.

Challenges Facing Projects

Currently, the demand for blue carbon credits is outpacing the amount of certified credits available for purchase. Barriers impeding development include the complexity of the ecosystems involved, knowledge gaps, and funding for developing the carbon market and for projects themselves. While research and methodologies are being developed for coastal projects, the methodologies still need to be adopted by those managing carbon markets and made more efficient. Such methodologies still need to be developed for projects further offshore.

The complexity of blue carbon ecosystems can make accurate carbon accounting difficult, especially those projects that will be underwater. For instance, while mangrove stocks can be estimated and monitored with satellites and drones, submerged seaweed cannot be as easily estimated and new technologies, proxies, or in situ samples may be needed. Mangroves, salt marshes, and seagrass beds currently have methodologies and standards for determining carbon benefits, but seaweed project methods need further research and are currently under development.

For instance, Verra, which manages the world’s leading voluntary carbon markets program, the Verified Carbon Standard (VCS) Program, has developed methodologies for tidal wetlands and seagrass restoration and coastal wetland creation. Verra, Area of Focus: Blue Carbon (2022). Project teams can use these methodologies for their projects to quantify emission reductions and removal benefits. Verra will then issue Verified Carbon Units (VCUs) that can be sold on the voluntary carbon market. In comparison, in 2021, Verra launched the Seascape Carbon Initiative to kickstart the carbon credit process for marine carbon activities, including seaweed. Goals of the initiative include research, developing carbon crediting methodologies, and finding financing for marine blue carbon projects. Yet, to date, methodologies have not been finalized. Verra, Seascape Carbon Initiative (2022).

Additionality, meaning the carbon mitigation would not have occurred without the project, can also be a challenge for blue carbon projects. Establishing additionality can be a challenge if other incentives or laws, regulations, or government policies are encouraging conservation, restoration, or other activities in the area. If a blue carbon project overlaps with a marine protected area or with “national conservation priorities … [or] sustainable coastal wetlands management,” demonstrating additionality could be difficult for the project if carbon sequestration would happen on its own without the blue carbon project. Conservation Int’l et al., supra, at 20. However, there are also benefits for locating blue carbon projects in these areas. For instance, the UN Global Compact Ocean Stewardship Coalition has noted the dual benefit of co-locating a seaweed farm with a marine protected area to enhance the benefits to biodiversity and fisheries.

Complex Offshore Ownership

A study focused on blue carbon projects on publicly owned coastal wetlands noted that the feasibility of projects is complicated by coastal property rights as the property line between private property and publicly owned resources is always changing. Read Porter, Cody Katter, & Cory Lee, Legal Issues Affecting Blue Carbon Projects on Publicly-Owned Coastal Wetlands (Sea Grant L. Fellow Publ’ns 96, 2020). These shifting lines can complicate determinations regarding who owns the coastal property and therefore has rights to the generated carbon credits.

For most property owners, property boundaries are fixed, set out in metes and bounds in property deeds. But such static conceptions of property do not work along the coasts where the shoreline is constantly changing. A different set of legal rules has evolved to govern coastal property boundaries. Changes to coastal property lines can happen because of (1) accretion, which is the gradual, imperceptible addition of sand or sediment to a shoreline; (2) reliction, which occurs when water withdraws from a shoreline and uncovers new dry sand; (3) erosion, which occurs when water gradually removes land from the shoreline; and (4) avulsion, which is the sudden, apparent addition to or loss of land due to water action, such as changes due to a hurricane.

Generally speaking, the property line between private coastal property and state submerged lands moves when changes are the result of the natural forces of accretion, reliction, and erosion. As the shoreline moves, the property lines move. Any land that is gained through accretion will belong to the shoreline property owner, while any land lost through erosion will belong to the state.

Shorelines, however, can also change due to human activity that results in artificial accretion or erosion. Dredging projects and the installation of jetties, groins, and living shorelines can all change how sand moves along a beach. State courts have found that in the case of artificial accretion, the private waterfront property owner can only claim title to the new land if they did not cause, consent to, or participate in the project that caused the accretion. See Reid v. State, 373 So. 2d 1071, 1072 (Ala. 1979). If the property owner, or a prior property owner, played a role in the accretion, the new land belongs to the state.

Unlike gradual changes to the shoreline, an avulsing event, such as from a storm event, does not change the property line. Greenfield v. Powell, 118 So. 556, 558 (Ala. 1928). Therefore, following an avulsing event, an oceanfront property owner does not lose property that is covered by water to the state, nor does the landowner take title to any additions of dry land.

An additional complication is that the neighbor for these shoreline property owners is the state, who holds the submerged lands and waters in trust under the public trust doctrine. The public trust doctrine establishes that states hold the title to the tidelands and submerged lands below navigable waters in trust for the benefit of the residents of the state.

The seminal U.S. Supreme Court case on the public trust doctrine is Illinois Central Railroad Co. v. Illinois, 146 U.S. 387 (1892). In that case, the Court outlined the contours of the trust and differentiated it from other property interests, stating that “the state holds title to the lands under the navigable waters” of the state “in trust for the people of the state, that they may enjoy the navigation of the waters, carry on commerce over them, and have liberty of fishing therein freed from the obstruction and interference of private parties.” Id. at 452. The Court also prohibited the alienation of trust property unless the transfer benefits the trust, such as through the building of wharves and docks.

Thus, all states must manage their public trust resources to these standards. However, states can extend the public trust to more lands or more uses within their state, and many state courts have noted that the trust is not static and should evolve to accommodate changing conditions and the public’s needs. However, the public trust doctrine can complicate blue carbon projects, as the state may not be able to transfer away carbon credits with a monetary value unless the project is consistent with the trust. As discussed further below, some states are actively permitting seaweed farms within state waters, but questions remain. Consequently, can the state sell carbon credits for seaweed blue carbon projects? Project proponents will need to convince state regulators that the projects are consistent with the public trust doctrine.

Traditional land use regimes must also be respected and community members must be made aware of who had the right to and can transact for the blue carbon credits.

A further complication is that submerged lands may be owned by private parties, the federal government, or tribes. In Washington, for example, around 50% of Washington tidelands belong to Treaty Tribes or private landowners. Large-scale seaweed projects can also interfere with other coastal users, such as fishermen or tribes. Consultation with these parties may be preferable or even required, which could delay, alter, or prevent a blue carbon project. Project developers must work through who owns the project’s land resources and who is entitled to the carbon rights. Traditional land use regimes must also be respected and community members must be made aware of who had the right to and can transact for the blue carbon credits. Porter, Katter, & Lee, supra, at 17.

State Permitting

Multiple states currently have active seaweed industries, including states in the Northeast, on the West Coast, and in Hawaii. Maine has the most robust industry at the moment, with more than 30 active farms. The Maine Department of Marine Resources has permitted over 100 sites to grow seaweed or seaweed alongside shellfish. In 2020, Maine growers harvested 500,000 pounds of seaweed (wet weight). Alaska’s seaweed industry is also growing, with 536,390 pounds of seaweed (verified) in 2021, which is up from 231,015 pounds in 2020. In 2021, the state had 11 seaweed farms permitted, with five actually farming, along with 17 seaweed/shellfish farms permitted, with 14 farming. See Sea Grant National Seaweed Hub, State of the States: Status of U.S. Seaweed Aquaculture (2023).

Although not as robust as Maine or Alaska, New Hampshire, Massachusetts, Rhode Island, Connecticut, and Washington all have active commercial farms in their state. Thus, the regulatory system on the state level exists for seaweed farming in many states that have the corresponding climate to grow robust seaweed.

Federal Seaweed Permits

Blue Carbon projects may need permits from the federal government. Rivers and Harbors Act (RHA) § 10 requires that regulated activities conducted below the high-water line of our nation’s navigable waters be approved and permitted by the U.S. Army Corps of Engineers (Corps). 33 U.S.C. § 403. Under Clean Water Act (CWA) § 404, the Corps is authorized to permit the discharge of dredge and fill material into navigable waters. 33 U.S.C. § 1344.

An uncertain and newly developing federal permit system could serve to stall seaweed blue carbon permits.

The Corps authorizes projects under section 404 and section 10 through either individual or general permits. General permits authorize common activities that will have only minimal individual and cumulative environmental impacts. A nationwide permit (NWP) is a type of general permit that authorizes activities across the country. It is important to note that, despite its name, an NWP may not apply everywhere in the country. The Corps’ 38 districts implement the regulatory program for each NWP, so the use of general permits is not uniform throughout the districts.

On January 13, 2021, the Corps published a final rule for modified and new NWPs, including NWP 55 for seaweed. Reissuance and Modification of Nationwide Permits, 86 Fed. Reg. 2744 (Jan. 13, 2021) (to be codified at 33 C.F.R. ch. 11). The new NWPs became effective on March 15, 2021.

NWP 55 is a new permit for seaweed mariculture operations and notes the potential for the seaweed industry in the United States. The permit only covers the RHA. Regulated activities can include such things as the placement or removal of structures, dredging, filling, excavation, or any other disturbance of sediment or modification of a navigable waterway. The Corps has taken the position that activities under the permit do not result in discharges that would implicate the CWA. Id. at 2,852. Further, NWP 55 only authorizes structures and does not authorize any of the operational aspects of seaweed aquaculture activities. NWP 55 also allows for multi-trophic mariculture operations, meaning the farm could be a mix of seaweed, finfish, and shellfish. The NWP also requires a preconstruction notification to the Corps District Engineer.

Uncertain Future

Sequestering carbon with seaweed could potentially play a role in meeting net-zero carbon emissions, but certain barriers remain for projects. Further research is needed to help determine how much carbon is sequestered by seaweed cultivation and to develop methodology for developing carbon credits. For projects in state waters, will regulators deem seaweed blue carbon projects to be compatible with the public trust doctrine and will the state be able to sell away carbon credits? Other users and owners of coastal land will need to be considered and may be required to be consulted with on projects.

In federal waters, permitting aquaculture projects are still in their infancy. Despite a new NWP for seaweed aquaculture, few aquaculture projects have been permitted in federal waters. Federal permits have been granted to several entities in the U.S. Exclusive Economic Zone. This includes a Special Coral Reef Ecosystem Fishing Permit, which NMFS first issued to Kampachi Farms in 2011; an RHA section 10 permit, which the Corps issued to Catalina Sea Ranch in 2014; and a CWA section 402 permit, which the EPA issued to Ocean Era in 2020. An uncertain and newly developing federal permit system could serve to stall seaweed blue carbon permits.

The U.S. Department of Energy’s Advanced Research Projects Agency–Energy has developed the Macroalgae Research Inspiring Novel Energy Resources (MARINER) program to develop tools to enable the United States to become a global leader in the production of marine biomass. The MARINER program is providing research funds for projects to develop tools for all aspects of seaweed production offshore. Seaweed blue carbon projects can definitely benefit from this research and development. One MARINER project is located nine miles offshore the coast of New Hampshire, showing that these operations can be permitted, at least on the experimental level. However, growing seaweed for biomass is another use of seaweed that could take precedence over carbon projects.

One final criticism of blue carbon seaweed projects that would sink seaweed deep in the oceans is that such projects could take away food sources from a growing world population that may face food scarcity in the future. This can serve as another barrier to developing seaweed to generate carbon credits. That said, if science can support generating carbon credits for seaweed blue carbon projects, seaweed and blue carbon could be a viable option in helping to achieve net zero.