A recent study published in Global Change Biology and led by Prof. FENG Xiaojuan from the Institute of Botany of the Chinese Academy of Sciences revealed a transcontinental divergence in soil carbon stock responses to decades of wetland drainage, which challenges the assumption that drainage generally causes wetland soil organic carbon (SOC) loss.

Researchers selected 29 pairs of drained and waterlogged sites including 188 soil profiles and 2437 subsamples and spanning low- to high-latitude wetlands in China and Finland, and conducted a transcontinental, pairwise survey. Through high-resolution sectioning of soil cores and the equivalent ash mass method, they compared SOC stocks in the drained and waterlogged soil profiles to avoid potential bias caused by bulk density change.

The results showed that drainage increased SOC stocks by 46±27% in carbon-poor wetlands, due to enhanced plant inputs; in contrast, SOC stocks decreased by 32±10% in carbon-rich wetlands following drainage, primarily due to the replacement of Sphagnum with vascular plants and enhanced decomposition.

Moreover, researchers revealed that drainage alone, without post-drainage disturbances, had led to a 1.80 Gt SOC gain in China over the past century, surpassing afforestation-driven SOC gains in northern China during the past three decades by 7.5-fold.

This study presents the first transcontinental, pairwise assessment of drainage impacts on wetland SOC stocks across broad climatic and vegetational gradients. The findings highlight the overlooked climate mitigation potential of carbon-poor wetlands under shifting hydrological regimes.

Researchers suggest that future wetland conservation and restoration strategies should be tailored to specific wetland types. Incorporating this context-dependent framework into Earth system models will help improve projections of wetland-climate feedbacks and support more informed conservation and management efforts.