• Beneficial use for sustainable waterborne transport infrastructure projects (WG 214), 2023.
• Carbon management for port and navigation infrastructure (WG 188), 2019.
• Applying working with nature to navigation infrastructure projects (WG 176), 2018.
• Dredged material as a resource: options and constraints (WG 104), 2009.
• Ecological and engineering guidelines for wetlands restoration in relation to the development, operation, and maintenance of navigation infrastructures (WG 07), 2003.

Defining blue carbon

Blue carbon refers to the carbon stored in coastal and marine ecosystems. Mangroves, seagrasses and saltwater marshes capture, store and sequester carbon dioxide (CO₂) in plant and sediment rhizome biomass, forming the basis of BCE. When mangroves, seagrasses and saltwater marshes are lost, the carbon they have long stored is released into the atmosphere as CO₂ through oxidation, while the capacity of these habitats to sequester carbon in the future is diminished, if not lost entirely. What makes these marine coastal ecosystems important is their ability to store carbon continuously and indefinitely, for as long as the ecosystems remain intact.

Carbon markets

Carbon markets play an essential role in the management and conservation of BCE. Carbon markets provide financial incentives for the preservation and restoration of BCE by assigning a monetary value to the carbon sequestration capabilities of these ecosystems. These markets create a blue carbon economy that encourages stakeholders to invest in BCE conservation efforts (Pendleton et al., 2012).

Carbon markets generally require that BCE projects demonstrate “additionality” to support the establishment of project- specific carbon credits (Michaelowa et al., 2019). The 1998 United Nations (UN) Kyoto Protocol defines additionality as “reductions in emissions that are additional to any that would occur in the absence of the certified project activity” (Houston et al., 2024; UNFCC, 1998).

Protecting BCE is essential and can be leveraged in carbon markets where existing BCE is at risk. The REDD+ framework was established to protect existing habitat in developing countries – REDD stands for “reducing emissions from deforestation and forest degradation” and + stands for additional habitat activities that protect the climate, including sustainable management, conservation and enhancement of ecological carbon stocks (UN-REDD Programme, 2025). Under the REDD+ framework, developing countries can receive credit for emission reductions when they reduce habitat losses. Notably, REDD+ credits are not available in countries where BCE habitats already are protected. In Australia, for example, additional credit is not gained by “protecting” mangroves, which already require protection by law.

Carbon markets can be used to finance restoration and conservation projects through the sale of carbon credits generated from blue carbon projects. These credits are sold to entities looking to offset carbon emissions, creating a revenue stream that supports environmental sustainability (Duarte et al., 2013). By participating in carbon markets, BCE receives recognition and resources for its role in reducing atmospheric carbon, thereby contributing to global resilience to natural hazards (Murray et al., 2011). Participation in carbon markets requires rigorous monitoring and carbon-sequestration verification processes, which drives scientific research in understanding and measuring BCE. The Nature Conservancy (2024) provides a summary table of coastal wetland methods to calculate blue carbon credits. This paper does not summarise methods to quantify and verify BCE carbon storage.

While BCE, especially mangroves, seagrasses and salt marshes, are all highly efficient carbon sinks, other ecosystems (e.g., macroalgae, unvegetated tidal mudflats, coral reefs and ocean sediments) also serve as lesser or unknown carbon sinks (Howard et al., 2023). To date, carbon trading has targeted mangroves, seagrass and salt marsh BCE, while carbon metrics for other marine emerging environments (e.g., macroalgae, benthic sediments and mudflats), continue to be developed and may become actionable in the future (The Blue Carbon Initiative, https://www.thebluecarboninitiative.org).

Carbon sequestration potential in blue carbon ecosystems

BCE captures CO2 by sequestering the carbon in biomass and in underlying sediments (Figure 2), which includes natural organic carbon along with decayed biomass and detritus. In marine environments, sulphate reducing bacteria slow biodegradation and limit methanogenesis and methane release to the atmosphere. These processes form the basis for long-term carbon storage in marine coastal ecosystems. In freshwater environments, anaerobic decay and methane and CO2 production can reduce long-term and permanent carbon storage, though even in freshwater environments long-term carbon storage (termed teal carbon) is possible (Kayranli et al., 2010).

• Mangroves are intertidal forests known for trapping sediments and organic carbon. Mangroves shrubs and trees grow in coastal saline or brackish waters, primarily in equatorial climates and along coastlines and tidally influenced rivers (Figure 3). Mangroves are not solely equatorial and exist in temperate zones as well. The Blue Carbon Initiative estimates mangroves are being lost at a rate of 2% per year. Meanwhile, carbon emissions from mangrove deforestation account for up to 10% of emissions from deforestation globally. Global efforts to protect and restore mangrove forests have reduced mangrove loss rates from ~2% annually in the late 20th century to <0.4% annually in the early 21st century (Friess et al., 2019).
• Seagrasses and seagrass meadows are underwater ecosystems formed by seagrass and other marine plants found in shallow coastal waters and brackish estuaries. Seagrasses are submerged flowering plants that produce seeds and pollen and have roots and rhizomes anchored to the seafloor. According to The Blue Carbon Initiative, seagrasses cover less than 0.2% of the ocean floor and store roughly 10% of the carbon buried in ocean sediments each year. The Blue Carbon Initiative estimates that seagrasses have lost more than 30% of their historical global coverage and are being lost at a rate of 1.5% per year.
• Salt marshes are tidal wetlands that accumulate organic-rich peat layers, sequestering carbon over centuries. Salt marshes appear in the coastal intertidal zone and are regularly flooded by diurnal tides. Salt marshes (Figure 4) are populated by salt-tolerant plants that support the stability of coastal and estuarine environments. In addition to their long-term carbon storage capability, they play a vital role in the aquatic and terrestrial food webs and deliver nutrients to coastal waters. Tidal marshes have lost more than 50% of their historical global coverage and are being lost at a rate of 1 2% per year (The Blue Carbon Initiative).

Blue carbon ecosystems also have the unique advantage of accreting vertically in response to rising sea levels providing they have sufficient sediment supply (Mcleod et al., 2011). The sediment carbon sinks in these environments increase over time, greatly extending their longevity.

Sediment beneficial use can be used to enhance these processes, especially in degraded habitats subject to erosion, subsidence and habitat loss where the addition of dredged sediment can help maintain sediment elevations and healthy wetland habitat and aquatic ecosystems (Berkowitz et al., 2021, 2022a, 2022b; Bridges et al., 2021; Suedel et al., 2024). Mangroves, seagrasses, and wetlands continue to be at risk due to increasing seawater temperatures and sea level rise, increasing storm intensities, and anthropomorphic pressures including nearshore developments, thus limiting their ability to adapt and defend coastal environments against high-energy natural hazard events (Ondiviela et al., 2014).

Oceans absorb about 31% of the CO2 emissions released to the atmosphere (NOAA, 2025). While coastal habitats occupy less than 2% of the total ocean area, they account for about half of the carbon stored in ocean sediments (The Blue Carbon Initiative). Table 1, adapted from Mcleod et al. (2011), shows the blue carbon sequestration potential for mangroves, seagrass meadows and saltwater marshes compared to carbon sequestration in terrestrial forests. Globally, there are between 36 and more than 100 million hectares of BCE, but this coverage is only a small part of what existed historically and is frequently threatened by population growth and other coastal development pressures. The total annual carbon storage potential in blue carbon habitats ranges from approximately 60 to 204 teragrams carbon (Tg C, or 109 g C), while the annual carbon storage capacity of terrestrial forests is approximately 194 Tg C (Table 1).

The intersection of blue carbon and waterborne navigation infrastructure

Understanding the relationship between the WTI sector and BCE is essential for developing sustainable coastal management practices. Ports and navigation infrastructure that operate in marine coastal environments may be in proximity to coastal habitat where blue carbon resources (recognised or unrecognised) exist. While port and navigation operations can negatively impact BCE, thoughtful and proactive management practices may be used to protect and even enhance blue carbon resources. Such operations may include the coastal, estuarine and riverine flood protection measures and the beneficial use of dredged material (Suedel et al., 2024).

Opportunities for the WTI sector to protect, mitigate or enhance blue carbon resources include:

• Achieving net zero carbon emissions for WTI and new development projects.
• Aligning sediment beneficial use practices with habitat restoration and enhancement goals, and enhanced resilience to natural hazards.
• Restoring and enhancing habitat mitigate new development impacts to the environment.
• Applying Working with Nature and Nature-based Solutions (NbS) in operating or managing WTI.
• Creating and supporting community engagement with BCE.

Over the past decade, the US Army Corps of Engineers (USACE) and PIANC have advanced sustainability thinking with such concepts as Engineering With Nature® (https://ewn.erdc.dren.mil) and using Nature-based Solutions (Bridges et al., 2021). PIANC (www.pianc.org) developed the Working with Nature philosophy for WTI projects to advance coastal resiliency and habitat creation. In Europe, Ecoshape ((www.ecoshape.org) has advanced the Building with Nature paradigm to integrate NbS into WTI projects. Collectively, these nature-based initiatives have been leveraged to promote habitat improvement and coastal resiliency, from altering the surface or texture of submerged structures and thus creating or expanding aquatic habitats, to using natural infrastructure systems, such as islands, marshlands and mangroves to protect WTI and local communities from severe weather events.

While nature-based initiatives can be incorporated at any project stage, they are best considered early in project planning when flexibility is greatest. By maintaining a committed and proactive approach from a project’s start to finish, opportunities to support a blue carbon economy can be maximised, and importantly, frustrations, delays and unforeseen costs can be minimised.

Beyond improving sediment and habitat management, nature-based initiatives can be leveraged to optimise environmental conditions and optimise BCE. This involves first and foremost avoiding or minimising BCE losses and secondly using sustainable engineering design and project planning to restore and create new BCE. Meeting these objectives requires careful project planning and implementation, ecosystem and performance monitoring, and adaptive management. Adaptive management recognises that navigation projects rely upon learning and adaptation to optimise project outcomes, including reducing energy use and protecting the environment.

Waterborne transport infrastructure sector’s alignment with blue carbon

Comparison of Figures 5A and 5B highlight the multiple opportunities to incorporate infrastructure-related features into the design of a new or existing port located at the land-sea interface. The incorporation of BCE into WTI creates opportunities to increase the carbon storage capacity of the port while promoting biodiversity, plant and wildlife habitat, ecosystem services for public use and reduced risks to port/harbour assets by using these systems to absorb high intensity, natural hazards. Blue carbon ecosystems can be implemented in ways that incorporate engineering, economic, social and environmental benefits while minimising costs and burdens to port operations. Such opportunities exist in both the land- and sea-related environments that complement existing and future WTI.

The tidal prism and nearshore environments are areas where BCE can be enhanced, restored or created (King et al., 2022). Figure 5B shows how BCE can be implemented to complement conventional structures, such as breakwaters and jetties, where natural infrastructure features can be integrated into the design, contributing to more sustainable multiple lines of defence to reduce flood risk while promoting safe navigation. Nature-based designs also can enhance the environmental benefits of hardened structures. When considering the repair or modification of existing structures, natural infrastructure features can be integrated into the design to create hybrid solutions that include niches for enhancing habitat value that contribute to BCE while supporting WTI infrastructure requirements (Bridges et al., 2021; King et al., 2022).

Port navigation channels requiring maintenance to support port activities offer unique opportunities to use dredged material beneficially. Navigation channels can be oriented or shifted to reduce their impacts on sensitive marine environments. Dredged sediment considered suitable for beneficial use can be placed in ways to support BCE by enhancing submergent or emergent wetland habitats (Figure 5B). Such features, when designed with intent, can serve to reduce wave energy and erosion potential while providing ecosystem services. To the extent that these BCE features attract native species and marine wildlife, such habitats serve recreational, economic and other co benefits (Grothues et al., 2025).

Hybrid structures such as engineered artificial reef modules can be used to increase the habitat value of infrastructure elements that require more hardened materials to be effective. While not considered meaningful contributors to blue carbon, such structures can be used to reduce wave energy on BCE such as seagrasses while promoting sedimentation landward of existing reefs (Watanabe and Nakamura, 2018) and reducing the vulnerabilities of BCE structures to natural hazards (Storlazzi et al., 2025).

Management of upland infrastructure and habitat features to further support BCE

• Avoiding habitat loss.
• Restoring tidal connectivity.
• Rewetting drained organic soils.
• Restoring sediment to sediment-starved wetlands.
• Improving water quality.
• Replanting vegetation.

While upland features are not blue carbon systems, they can work with offshore blue carbon systems to enhance flood resiliency and can be used to integrate habitat features with port infrastructure. Natural infrastructure features such as earthen berms constructed to reduce flood risk or to mitigate noise can be designed as multipurpose structures that include low-maintenance native plant habitat and walking trails. Selectively, those same plants can serve as soil engineers to stabilise berm slopes to help reduce erosion.

Upland habitat features also promote freshwater rain infiltration to groundwater and subsequent groundwater migration to offshore BCE that depend on freshwater input (Santini et al., 2014). Bioswales can be constructed at street level and planted with low-growing native grasses and other vegetation features to reduce flooding and enhance groundwater recharge around parking lots, buildings and along roadways. Plant species selection considerations include species that are native and adapted to the region, provide wildlife habitat and food production, uptake stormwater pollutants and offer historical and cultural significance (Gaskin and Thomas, 2025). Pervious pavers can be used to promote additional groundwater infiltration, further enabling groundwater recharge.

Overall, natural infrastructure materials can be used to enhance the overall engineering, environmental and flood risk management benefits of WTI projects by reducing erosion, flood risk and the project’s carbon footprint. Sediment forms the foundation for nearshore aquatic habitat and dredged sediment can be used to supplement natural sedimentation processes forming a foundation for BCE and supporting upland habitat.

Utility infrastructure also plays a role in carbon management, as the installation of shore power (Figure 5B) can reduce carbon emissions and local air pollution associated with ships docked at port. Combined, these “green” features collectively contribute to sequestering carbon, contributing to reduced WTI carbon emissions.

Waterborne transport infrastructure sector contributions to blue carbon

While the potential physical impacts of the WTI sector to BCE are well understood, much less has been reported on the potential opportunities to protect and enhance BCE in the WTI sector. Here, we provide examples that link a key aspect of the WTI sector and the beneficial use of dredged material, to serve as a foundation for BCE and carbon storage.

The USACE navigation project on the lower Atchafalaya River in coastal Louisiana is an example of sediment beneficial use to create BCE in a brackish, estuarine environment. Tidally influenced, Horseshoe Bend Island was created through multiple strategic placements of dredged material over a 12 year period, using the river’s energy to shape the placed material to form the island (Figure 6). Foran et al. (2018) reported carbon sequestration results associated with wetland habitat created on the 35 ha Horseshoe Bend Island. Since 2018, Horseshoe Bend Island has nearly doubled in size and is approximately 60 ha.

Foran et al. (2018) reported emissions reductions due to a shortened navigation channel of 1.13 km (0.7 nautical miles) and lower rates of shoaling resulting in reduced dredging requirements and safer vessel transits. Horseshoe Bend Island sequesters an average of 5,220 kg of carbon per year. The shortened navigation channel reduces annual emissions by approximately 186 million metric tonnes of carbon dioxide equivalents based on the amount of fuel saved per trip and the number of trips made each year by commercial tugs and ships.

Other ecosystem services associated with Horseshoe Bend Island include increased habitat value for flora and fauna, reduced dredging costs and nutrient sequestration, which in turn reduces the nutrient load delivered to the Gulf of Mexico where hypoxia is an ongoing concern (Foran et al., 2018). The results of this innovative project demonstrate reductions in carbon emissions from reduced commercial vessels transit distances, less frequent dredging (reduced dredger-associated emissions) and BCE on the newly created island.

Berkowitz et al. (2021; 2022a, b) conducted ecosystem and engineering benefits assessments of six dredged material habitat improvement projects that were constructed more than 40 years ago, documenting the long-term benefits of dredged material beneficial use. Four of the projects were in marine/estuarine coastal environments where post-construction beneficial use monitoring data were available for comparison to natural reference locations (Figures 7 and 8). As part of the assessment, soil samples were collected and analysed for multiple physicochemical characteristics, including loss on ignition for percent organic matter (LOI) and total carbon measurements, both relevant for assessing blue carbon benefits.

The results of the four projects consistently showed improvements in soil physicochemical properties with age, including increased carbon content. The LOI and total carbon concentrations increased over time and, in most cases, approached the values observed in reference locations. This trend demonstrated that carbon is accumulating in the beneficial use sites (Berkowitz et al., 2022a). However, the amount of soil carbon in the beneficial use sites was lower than values reported at natural reference locations – even decades after project implementation and even when habitat characteristics and vegetation composition showed significant similarities with undisturbed areas. These results align with findings from others reporting blue carbon accumulation in created coastal marshes (Yu et al., 2017; Abbott et al., 2019).

Overall, results showed that 40 years after construction, the four study sites maintained the soil physical substrate necessary to support healthy plant communities and ecological functions of their respective habitats (Berkowitz et al., 2022b). Carbon sequestration and other benefits were achieved without post-construction management or intervention. Collectively, using dredged material for habitat restoration demonstrates the potential for novel nature- based applications for the WTI sector to contribute to BCE.

Conclusions

While there is growing evidence for the benefits of blue carbon in marine coastal environments, few studies have reported on the intersection of the WTI sector and blue carbon resources. Known adverse impacts associated with WTI projects include carbon emissions from the world’s dredging fleet, the release of carbon when BCE bottom substrates are disturbed by dredging activities and the loss of BCE when new ports and other WTI projects are constructed around existing habitat. Yet the beneficial use of dredged material, especially material removed from navigation channels, has received scant attention for its potential for providing opportunities to enhance, restore and create BCE.

In established ship channels, sediment beneficial use can offer an opportunity to increase WTI contributions to BCE (Figure 8). Sediment beneficial use offers several advantages: 1) it can create or enhance habitats; 2) it promotes resource circularity within the tidal prism or watershed; and 3) it reduces the release of CO₂ by limiting the oxidation of organic carbon in dredged sediment. While sediment removal over short periods contributes less to carbon storage, deepening or widening channels can significantly reduce BCE by disturbing aged substrates with long-term carbon storage. Sand, silt and clay suitable for beneficial use should be relocated to promote BCE and to contribute to long-term carbon storage. Disposal of dredged material offshore releases stored carbon and reduces potential benefits, as it only aims to remove sediment from the channel.

While the economic situations of developed countries and countries in transition are quite different, the opportunities to leverage natural processes and to integrate nature into WTI planning are universal. Greater focus must be applied to impacts on BCE, which intrinsically supports marine coastal habitat. New infrastructure developments are expected to yield the most benefits during a project’s early development stages when integrated with existing habitats and avoiding habitat loss. Greater understanding of the natural processes affecting a project and how natural processes can be integrated into project designs reduces environmental and social risks associated with coastal development.

Two approaches should be at the forefront of WTI project design concepts to protect BCE and generate carbon credits: 1) how best to protect existing habitat; and 2) how to promote and create new habitat. The integration of nature-based initiatives with WTI projects can be leveraged to enhance existing environments, hence the “with nature” aspect of these initiatives.

All WTI projects have environmental impacts, which should be offset by enhancing and creating new habitats. The increased use of carbon trading models facilitates the use of blue carbon to meet or offset mitigation requirements. Sediment beneficial use and nature-based initiatives can be employed to create new BCE. Practitioners are encouraged to understand how BCE is traded in voluntary carbon markets and how to leverage carbon markets for blue carbon habitat investments. Blue carbon projects must protect existing habitats and demonstrate “additionality” when establishing project-specific carbon credits (Michaelowa et al., 2019).

PIANC EnviCom WG256 is developing guidance to promote these concepts. The guidance will define blue carbon and explain its relevance to WTI. The WG is gathering and reviewing information about international blue carbon initiatives, both in relation to WTI and, where relevant, other marine and coastal sectors including nature protection. The guidance will identify and present examples (case studies) that turn theory into practice. These case studies will include not only designed and implemented blue carbon projects but also examples showing evolving standards and markets.

The current information suggests that meaningful opportunities exist for the WTI sector to increase its contribution to blue carbon. However, significant gaps remain in our understanding of how blue carbon-related WTI activities can be implemented. Addressing these gaps will become increasingly important in the future due to the vulnerability of ports and other marine infrastructure facilities to natural hazard extremes. Blue carbon offers an opportunity to contribute meaningfully to BCE while simultaneously achieving a more sustainable, resilient and less vulnerable WTI sector.

Summary

This article examines the crucial role of blue carbon ecosystems (BCE) – mangroves, tidal marshes, seagrasses – in capturing carbon in marine environments and the role of waterborne transport infrastructure (WTI) to protect and restore BCE. Blue carbon ecosystems are vulnerable to pressures from WTI, such as ports and shipping lanes. We explore the impact of port activities on BCE and review current mitigation strategies, emphasising integrated approaches for sustainable coexistence. Working with Nature and sediment beneficial use can be leveraged through collaboration among marine transport authorities, environmental managers, scientists and engineers to protect these essential carbon sinks while supporting economic contributions from the WTI sector.

Blue carbon environments are essential to sustaining the marine coastal environment. They sequester carbon while also creating essential habitat for fish and wildlife. They also help reduce flood risks and associated vulnerabilities to nearshore communities and can be used to help protect ports and other WTI facilities from floods and high-energy events by absorbing wind and wave energy. While the creation of BCE can help protect our coastal communities, the loss of BCE risks exacerbating the potential for harm.

Carbon markets play an essential role in the management and conservation of BCE - they provide financial incentives for the preservation and restoration of BCE by assigning a monetary value to the carbon sequestration capabilities of these ecosystems. These markets are designed to encourage stakeholders to invest in BCE conservation efforts.