A Chinese study has quantified 20 years of carbon sequestration in wetlands

Research by the Chinese Academy of Sciences reveals that wetlands sequestered an average of one billion tons of carbon per year in the first two decades of the century. Seventy percent of this capture takes place in tropical areas

by Matteo Cavallito

 

Wetlands, according to estimates, occupy just 6% of the Earth’s surface but sequester more than 30% of the carbon found in the global soil. However, the difficulties in detecting the dynamics of this phenomenon make quantitative assessments of their contribution especially complicated. With obvious implications for the development of strategies to protect these environments and help climate mitigation.

A recent study in China has provided a possible answer to this problem. Using a new dynamic global database of water levels in these ecosystems, it attempted to assess the spatial and temporal dynamics of carbon sequestration from 2000 to 2020.

 

Twenty years of observations

“Terrestrial carbon (C) sink has long been recognized as trending upwards, yet its recent slowdown raises concerns about accelerating climate change,” says the research published in the journal Nature Ecology & Evolution. “Variations in wetland C sequestration are hypothesized to play a key role in this shift. Here we mapped annual water levels in global wetlands from 2000 to 2020 using 2,295 field-based measurements.”

This allowed the authors to evaluate “the spatiotemporal pattern of wetland net ecosystem production (NEP) in conjunction with other environmental factors.”

The researchers compiled 934 in situ observations from 258 peer-reviewed publications and the global FLUXNET database. In this way they estimate an average net ecosystem production (NEP) of wetlands globally. The analysis integrated the information with other environmental data and machine learning models based on artificial intelligence.

Tropical wetlands contribute to 70% of sequestration

All things considered, researchers led by Ding Weixin, professor at the Institute of Soil Science of the Chinese Academy of Sciences, estimated an average annual global carbon sequestration in wetlands of one billion tons of carbon in the period 2000-20. The phenomenon is concentrated in South America, Asia, and Africa. These regions, in fact, contribute 79% of total global sequestration. Worldwide, the contribution of wetlands located in tropical areas accounts for 70% of the total amount.

The study also revealed that global carbon sequestration in wetlands has remained largely stable over the two decades, with a reduction in South America offset by increases in Africa, North America, Asia, and Europe.

Hydrological changes, the researchers note, are the main factor driving the increase in regional variability in carbon sequestration in wetlands. At the same time, they add, “intensifying hydrological extremes under climate change may undermine the resilience of wetland C sinks and the ecosystem services they support.”

But the growth of carbon sinks is slowing down

Finally, the study found a decrease in the long-term growth rates of terrestrial carbon sinks. In fact, the increase in these sinks has slowed from an average of 75 billion tons of carbon per year between 1980 and 1999 to 37 billion per year between 2000 and 2020.

“These findings provide a crucial new perspective: The leveling off of wetland carbon sequestration has significantly contributed to slowing the increase in global terrestrial carbon sink in recent decades,” the researchers explain in a statement. The study, they add, therefore provides new data useful for global carbon assessment reports. Including those of the Intergovernmental Panel on Climate Change (IPCC) as part of efforts to combat global warming.