Soil erosion by water impacts soil organic carbon stocks and alters CO 2 fluxes exchanged with the atmosphere. The role of erosion as a net sink or source of atmospheric CO 2 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 CO 2 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 CO 2 of 45 ± 25 Mt C·y , 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 ), occupy only 1.5% of the total area suffering water erosion, but contribute 19.3% to the national erosion-induced CO 2 sink. The erosion-induced CO 2 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 CO 2 in the terrestrial budget, hence reducing the level of uncertainty.land−atmosphere CO 2 flux | soil carbon displacement | water erosion | national scale T errestrial ecosystems are a net sink of anthropogenic CO 2 globally (1, 2) but can be net sources or sinks regionally [e.g., Northeast Region of China (3)]. Knowledge of the distribution, magnitude, and variability of land carbon fluxes and underlying processes is important both for improving model-based projections of the carbon cycle and for designing ecosystem management options that effectively preserve carbon stocks and enhance carbon sinks. Despite considerable efforts made by the research community, the mechanisms governing uptake or release of carbon from land ecosystems are still poorly quantified (4).Soil erosion occurs naturally but is accelerated by human cultivation of the landscape, and modifies CO 2 exchange (5) between the soil and atmosphere. Soil erosion destroys the physical protection of carbon in soil aggregates and accelerates decomposition, inducing a net CO 2 source. Continuous erosion over a long period can destabilize carbon in deeper soil horizons and trigger its decomposition e.g., as conditions of temperature and moisture become more favorable (6, 7). Soil erosion also decreases nutrient availability and reduces soil water holding capacity, affecting ecosystem productivity (8) with feedback to the ecosystem carbon balance. However, because only a fraction of eroded carbon is lost to the atmosphere, the rest may be lost to streams and rivers and eventually delivered to marine ecosystems or deposited in the landscape. With the fine and light soil particles p...

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