Abstract

Soil erosion by water impacts soil organic carbon stocks and alters CO₂ fluxes exchanged with the atmosphere. The role of erosion as a net sink or source of atmospheric CO₂ remains highly debated, and little information is available at scales larger than small catchments or regions. This study attempts to quantify the lateral transport of soil carbon and consequent land−atmosphere CO₂ fluxes at the scale of China, where severe erosion has occurred for several decades. Based on the distribution of soil erosion rates derived from detailed national surveys and soil carbon inventories, here we show that water erosion in China displaced 180 ± 80 Mt C⋅y⁻¹ of soil organic carbon during the last two decades, and this resulted a net land sink for atmospheric CO₂ of 45 ± 25 Mt C⋅y⁻¹, equivalent to 8–37% of the terrestrial carbon sink previously assessed in China. Interestingly, the “hotspots,” largely distributed in mountainous regions in the most intensive sink areas (>40 g C⋅m⁻²⋅y⁻¹), occupy only 1.5% of the total area suffering water erosion, but contribute 19.3% to the national erosion-induced CO₂ sink. The erosion-induced CO₂ sink underwent a remarkable reduction of about 16% from the middle 1990s to the early 2010s, due to diminishing erosion after the implementation of large-scale soil conservation programs. These findings demonstrate the necessity of including erosion-induced CO₂ in the terrestrial budget, hence reducing the level of uncertainty.