Water erosion is the most active process controlling soil formation and evolution, which can affect the redistribution of carbon between terrestrial, aquatic, and atmospheric ecosystems. Erosion-induced organic carbon dynamic process should not be missing in terrestrial carbon cycle simulations.

However, due to an insufficient transfer of knowledge regarding soil erosion and carbon dynamics from smaller to larger scales, existing models at a large temporal and spatial scale present conflicting views on whether the net impact of erosion on carbon cycling acts as a carbon source or sink.

In a study published in Science China Earth Sciences, researchers led by Prof. Li Zhongwu from the School of Geographic Science, Hunan Normal University, together with collaborators, have introduced an approach that combined a spatially distributed sediment delivery model and biogeochemical model to simulate erosion-induced soil organic carbon dynamic, confirming water erosion acts as a net sink of atmospheric CO₂ at the basin scale.

Applying this coupling model to the Dongting Lake Basin, which is the largest lake watershed in China, the researchers found that the annual average amount of soil erosion during 1980–2020 was 1.33×10⁸ t, displaying a decreasing trend followed by a slight increase.

Only 12% of the soil organic carbon displacement was ultimately lost in the riverine systems, and the rest was deposited downhill within the basin. The average lateral soil organic carbon loss induced by erosion was 8.86×10¹¹ g C in 1980 and 1.50×10¹¹ g C in 2020, with a decline rate of 83%. A net land sink for atmospheric CO₂ of 5.54×10¹¹ g C a^-1 occurred during erosion, primarily through sediment burial and dynamic replacement.

The researchers revealed that ecological restoration projects and tillage practice policies are still significant in reducing erosion, which could improve the capacity of the carbon sink for recovery beyond the rate of horizontal carbon removal. For example, after large-scale ecological restoration in Dongting Lake Basin, the recovery CO₂ sink exceeded the organic carbon lost to riverine systems. Eventually, soil organic carbon storage has increased.

By broadening the understanding of soil erosion and carbon dynamics, the researchers hope to provide more effective advice for maintaining soil health, enhancing carbon sinks in terrestrial ecosystems, and mitigating climate change.