Carbon on the Shoreline: From Coastal Clutter to Climate Solution
New research finds that storm-tossed seaweed may quietly fuel greenhouse gas emissions—and proposes an unexpected fix: biochar.
Breaking the Ice:
A new study is drawing attention to an overlooked climate actor: beach wrack. This decaying mass of seaweed, algae, and organic debris routinely deposited along coastlines after storms is more than just an eyesore or a nuisance to beachgoers. According to the study, wrack is also a surprisingly potent source of carbon dioxide emissions when left to decompose on shore.
The study measured CO₂ emissions on coastal plots with and without macrophyte beach wrack. The results were striking: CO₂ flux from wrack-covered areas was 23 times higher than in wrack-free zones. Even more compelling, when wrack was manually removed, CO₂ emissions dropped by 1.6 times. This suggests that beach wrack is not just passive debris, but an active contributor to greenhouse gas emissions from coastal soils.
But the study doesn’t just highlight a problem—it also proposes a potential climate solution: converting wrack into biochar. This process, the authors argue, could both mitigate emissions and sequester carbon in a stable, soil-enriching form.
Quick Melt:
Since climate change intensifies ocean eutrophication — when excess nutrient concentration accelerates algae growth — along with increased storm activity, seaweed is increasingly likely to wash ashore. Unless action is taken, this could result in more carbon being quietly released into the atmosphere. The decomposition of wrack not only produces greenhouse gases but also exacerbates beach pollution, introduces pathogens, and can be hazardous to both ecosystems and public health.
Turning wrack into biochar, a charcoal-like substance created through pyrolysis, could offer a win-win: cleaner coastlines and a form of carbon sequestration. Biochar is celebrated for its ability to store carbon long-term while improving soil health. Though seaweed-based biochar has lower carbon content than that made from terrestrial biomass, its high pH and nutrient richness offer unique agricultural advantages.
The researchers advocate for organized collection efforts—especially after storms—to gather wrack before it decays. However, they caution that this approach must be economically and ecologically viable, requiring careful study of logistics, seasonal variability, and full lifecycle emissions.
The Thaw:
How Does Carbon Flow Through Coastal Ecosystems? AccumulationZone Explains.
When seaweed grows in the ocean, it acts as a carbon sink, pulling CO₂ from the water through photosynthesis. But once it detaches and washes ashore, the carbon stored in that biomass begins to re-enter the atmosphere. Microbial decomposition is the main culprit: as bacteria break down the organic material, they respire CO₂, effectively reversing the earlier carbon capture.
This shift from sink to source is part of a broader phenomenon known as the coastal carbon cycle. It's a dynamic system, where vegetation, sediments, and microbial life constantly exchange carbon with the atmosphere. But when decomposition is rapid and unchecked—like it often is in nutrient-rich, storm-hit beach zones—the net effect can be a release of greenhouse gases, not storage.
Enter biochar. By pyrolyzing the seaweed under controlled, oxygen-limited conditions, the process locks much of the carbon in a stable form that resists microbial breakdown. This same principle has been used for terrestrial plants, but marine biochar research is still emerging. The chemical composition of algae-derived biochar is different—lower in carbon, but richer in nitrogen and minerals. Understanding how these differences affect both carbon sequestration potential and soil application is a key area for further investigation.
The study also gestures toward a promising frontier in carbon accounting: real-time, field-based measurement. Using portable gas analyzers like the Picarro G4301, the researchers moved beyond theoretical modeling to capture direct emissions under various wrack conditions. This empirical approach helps refine our understanding of coastal emissions—a vital step if nature-based climate solutions are to be accurately evaluated and scaled.
Final Thoughts
Far from being inert debris, decomposing seaweed represents a biologically active interface where microbial respiration drives substantial carbon emissions. Strategic intervention—such as converting biomass to biochar—could transform these ephemeral sources of emissions into long-term carbon sinks, offering scalable, ecosystem-based approaches to climate mitigation.