Mangroves are among the world’s most effective natural carbon stores, but new research suggests that their ability to trap carbon may weaken as sea levels continue to rise.
These salt-tolerant coastal forests occupy less than 1% of the Earth’s surface, but hold about 15% of all carbon stored in marine ecosystems. Most of that carbon is locked up in the soil beneath the trees, making mangroves important allies in efforts to slow climate change.
While some previous studies have shown that rising sea levels may increase carbon storage in mangrove ecosystems, new research paints a more complex picture.
Rising sea levels could reduce mangrove carbon storage
Researchers led by the University of Exeter, in collaboration with partners in Colombia and the United States, have created a new computer model to investigate how rising sea levels will affect carbon storage across mangrove forests.
Their findings suggest that while certain areas may temporarily accumulate more carbon as water levels rise, the overall carbon storage capacity of mangrove forests is likely to decline over the next century.
“Mangrove forests are extremely important for slowing climate change because they are efficient carbon sinks,” said Dr Arya Iwantoro, who conducted the research at the University of Exeter and is now based at the University of Plymouth.
“Studies on mangrove carbon storage are typically based on field observations, and such studies have found that carbon storage can increase as sea levels rise.
“However, this alone may not reveal the broader picture of what is happening throughout the forest.
“To investigate this, we developed a new model that links water flow and sediment transport, mangrove growth and mortality, and carbon storage, while tracking changes in the composition of the mud layer in which mangroves grow.
“Effectively, we have created three models in one to assess how these complex ecosystems will respond to sea level rise.”
Why mangroves are “drowning”
The model showed that rising sea levels could initially increase carbon accumulation in some locations. However, if conditions continue to change, wider forests may lose their ability to effectively store carbon.
Luisa Fernanda Gómez Vargas, also from the University of Exeter, said: “Mangrove plants are highly specialized and require a period of inundation with each tide.”
“After this period, the site is no longer suitable; the plants “drown” and the mangroves die.
“Dying and erosion of carbon-rich soils can transform mangroves from carbon sinks (carbon storage) to sources (carbon release).”
As mangroves die and carbon-rich soils erode, trapped carbon can be released into the environment.
Increased sea level rise means increased carbon loss
The research team evaluated several sea level rise scenarios developed by the Intergovernmental Panel on Climate Change (IPCC). The analysis showed that increasing levels of sea level rise will have an increasing negative impact on mangrove carbon storage.
Dr Baend van Maanen, who leads the Mangroves and Carbon Project at Exeter, said: ‘Mangroves face an uncertain future due to climate change and human impacts on rivers and coasts.
“Mangroves are not only important carbon stores, they protect coasts from storms, provide livelihoods for coastal communities, and provide habitat for a wide range of species.
“Our findings highlight the importance of understanding coastal landscapes as a whole when predicting how mangroves will respond to climate change and how they can be protected.”
In addition to storing carbon, mangroves play an important role in protecting coastlines from storms, protecting wildlife, and helping sustain coastal communities. Researchers say the results highlight the importance of considering the entire coastal system when planning for climate change and protecting these precious ecosystems.
This research was funded by the Natural Environment Research Council.
The research results were published in a magazine the future of the earth In a paper titled “The importance of scale for the future of mangrove blue carbon under rising sea levels.”
