Salt marshes, critical coastal wetlands known for their exceptional ability to trap carbon, are expanding in some regions, but a new study reveals that the overall soil carbon they store is still declining. The loss is largely due to the destruction of older, mature marshes, especially in the southern United States, outpacing the gains from newly established areas.
- Salt marshes store carbon at rates about 40 times higher than forests on land.
- Destruction of mature marshes causes major net losses of stored soil carbon.
- China's integrated restoration efforts have improved salt marsh carbon storage.
What happened
Salt marshes—coastal wetlands flooded by seawater—play a vital role in trapping and storing carbon at extraordinary rates, far exceeding those of terrestrial forests. However, a recent study measuring surface soil organic carbon (SOC) between 2002 and 2019 found a troubling trend: a net loss of roughly half a million metric tons of SOC globally. This loss is mostly attributed to the destruction of older, mature salt marshes, which hold substantially more carbon than newly formed marshes. The southern United States emerged as a hotspot for these losses, impacted heavily by hurricanes and decades of industrial activities including oil drilling and agricultural runoff.
Notably, Louisiana’s Gulf Coast has suffered severe damage from hurricanes Katrina and Rita, where violent storms destroyed valuable marsh wetlands and converted them into open mudflats. The resulting release of stored carbon equated to the emissions of thousands of passenger cars over less than two decades. Similar damages continued with later hurricane seasons, compounded by rising sea levels. While some regions reported expansion of salt marsh areas, the carbon stored in soils has not matched these gains, highlighting a disconnect between area restored and ecosystem function.
Why it feels good
Despite these challenges, all is not lost. Asia, especially China, has demonstrated notable progress in reversing carbon losses in salt marsh ecosystems. Since 2002, China has added nearly a million metric tons of surface soil organic carbon by effectively expanding and restoring salt marsh habitats with a combination of natural land recovery and human-led treatments. This comprehensive approach, from top-level design to grassroots implementation, has made restoration faster, more cost-effective, and scalable for coastal nations worldwide.
Salt marshes themselves offer more than just climate benefits. As essential habitats for fish, crabs, migratory birds, and other wildlife, they provide natural coastal defenses against storms and erosion, supporting both biodiversity and human communities. The study underscores their role as silent ecological guardians capable of storing carbon for centuries or millennia, a long-term asset in mitigating global climate change.
What to enjoy or watch next
Following the promising example set by China, coastal regions across the globe are increasingly exploring integrated strategies to restore salt marshes while safeguarding their rich carbon stores. Observation of restoration projects and policies worldwide can offer inspiring models for balancing ecological health with economic realities. Watching how innovative approaches combine natural recovery with targeted human interventions will be key to scaling these efforts successfully.
Moreover, keeping an eye on developments in hurricane-prone areas like the U.S. Gulf Coast is crucial, as rebuilding mature salt marsh ecosystems there can both protect people and restore vital carbon sinks. Conservationists, scientists, and policymakers are collaborating ever more closely to ensure these vulnerable habitats can thrive once more. Staying informed about these partnerships and emerging success stories helps us appreciate the resilience of nature and the power of community-driven solutions.