Researchers reveal role of wetlands in terrestrial carbon sink change

Wetlands are among the most efficient ecosystems for carbon (C) sequestration, storing more than 30% of global soil C in only 3–13% of Earth's land surface. However, the spatiotemporal patterns of wetland C uptake and their role in regulating global land C sink dynamics have been poorly quantified. As a result, wetlands have not been explicitly incorporated into the models used to constrain the global C budget, making it difficult to accurately estimate land carbon sink and formulate evidence-based wetland management policy.

To address this problem, a research group led by Prof. DING Weixin from the Institute of Soil Science of the Chinese Academy of Sciences has utilized a newly developed dynamic global wetland water level (WL) dataset to assess the spatiotemporal dynamics of wetland carbon sequestration from 2000 to 2020.

Their findings were published in Nature Ecology & Evolution.

The researchers compiled 934 in situ observations from 258 peer-reviewed publications and the FLUXNET database to estimate a global mean wetland net ecosystem production (NEP) of 56.4 g C m^‒2 year^‒1. By integrating the NEP dataset with environmental datasets and machine-learning models, they estimated a mean annual global wetland C sequestration of 1,004 Tg C for the period 2000–2020, with 70% contributed by tropical wetlands.

They discovered that South America, Asia and Africa were the top three continents for wetland C sequestration, collectively accounting for 79% of the global total.

The study further revealed that global wetland C sinks declined through 2005, followed by a subsequent recovery. Overall, global wetland C sequestration was roughly stable over the two-decade period, with gains in northern mid-high latitudes offsetting declines in the tropics and southern mid-high latitudes. At the continental scale, South America's capacity for wetland C sequestration decreased during the study period, completely offsetting collective wetland C sink gains in Africa, North America, Asia, and Europe. 

This study highlights hydrological change as a primary driver of increasing regional variability in wetland C sinks. It also notes that intensifying hydrological extremes resulting from climate change may undermine the resilience of wetland C sinks and the ecosystem services they support.

Finally, based on the estimates from Friedlingstein et al. (2022), the researchers found that terrestrial C sink growth rates decreased from 0.075 Pg C yr^‒2 (P < 0.05) during the period 1980‒1999 to 0.037 Pg C yr^‒2 (P > 0.05) during the period 2000–2020. The temporal trajectory of global wetland C uptake from 2000 to 2020 showed a positive correlation with terrestrial C sinks and can explain 33% of temporal variations in terrestrial C sinks.

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. All in all, this study provides important new data for global C evaluation reports such as those by the Intergovernmental Panel on Climate Change.