Distinguishing Erosion Effects on In‐Situ and Ex‐Situ Soil Organic Carbon at Varying Carbon Levels Using <scp>δ¹³C</scp>

ABSTRACT The effect of CO 2 emissions linked to soil erosion is a pressing global concern. However, the lack of robust methodologies has hindered a comprehensive understanding of the fate of soil organic carbon (SOC). This includes its redistribution, mineralization, and the factors influencing these processes. As a result, inconsistencies have emerged in estimating CO 2 emissions from eroded areas. This study investigated eroded slopes during the rainy season. We employed δ 13 C isotopic tracing to quantify SOC redistribution caused by erosion. Additionally, we also identified the sources of SOC mineralization substrates and their driving factors. Our goal was to delineate the distinct in‐situ and ex‐situ effects of erosion on CO 2 emissions from slopes with varying SOC levels. The results revealed that 1.4%–2.9% and 2.9%–5.1% of ex‐situ SOC were redistributed across erosion and sedimentary sites, corresponding to moderate to severe erosion. Of the total SOC mineralization induced by erosion, in‐situ and ex‐situ SOC substrates accounted for 0.7%–6.3% and 2.3%–2.8% of total slope SOC, respectively. In erosion sites, the mineralization ratios of in‐situ and ex‐situ SOC were 0.6%–5.7% and 1.8%–2.3%, while in sedimentary sites, these ratios were 0.8%–7.1% and 3.1%–4.0% respectively. Notably, SOC content and soil water content (SWC) exhibited contrasting effects on mineralization: SOC content negatively influenced in‐situ SOC mineralization, whereas SWC positively affected ex‐situ SOC mineralization. Specifically, SOC content exerted a stronger negative effect on in‐situ SOC, while SWC played a more significant positive role in ex‐situ SOC mineralization. Based on these insights into the dynamics of in‐situ and ex‐situ SOC during erosion, we recommend that CO 2 emission assessments from eroded slopes account for both in‐situ and ex‐situ effects, as well as SOC levels. Furthermore, measures to enhance soil erosion resistance and buffering capacity could reduce erosion‐driven SOC loss and potentially mitigate CO 2 emissions from eroded slopes, such as optimized irrigation, crop residue incorporation, and organic fertilizer application.