Purpose Understanding how rainfall intensity and slope mediate soil organic carbon (SOC) transport is key to assessing carbon loss dynamics in sloped red-soil croplands, yet how carbon losses are partitioned among surface runoff, interflow, and sediment remains poorly quantified and understood. Methods A rainfall simulator was used to produce 90 min rainfall events of three intensities (60, 90, or 120 mm h−1) for plots with two slope values (10° and 15°), with all possible combinations of rainfall intensity and slope tested (i.e., <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\mathrm I_{60,\;\;}^{10^\circ}\mathrm I_{90,\;}^{10^\circ}\;\mathrm I_{120,\;}^{10^\circ}\mathrm I_{60,\;}^{10^\circ}\mathrm I_{90,\;}^{15^\circ}\mathrm{and}\;\mathrm I_{120}^{15^\circ}\)</EquationSource> </InlineEquation>). Test plots were 3 m long, 1.5 m wide, and 0.6 m deep. Results The quantity of SOC migrating in the sediment (1,120–8,520 mg m−2), surface runoff (175.40–1,714.01 mg m−2), and interflow (1.61–92 mg m−2) was influenced by the rainfall intensity, slope, and their interaction (P < 0.05). The sediment to surface runoff to interflow ratio was 2:1 (excluding sediment SOC), 91:20:1, 2,236:450:1, 696:270:1, 1,079:246:1, and 1,047:246:1 for <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\mathrm I_{60,\;}^{10^\circ}\mathrm I_{90,\;}^{10^\circ}\mathrm I_{120,\;}^{10^\circ}\mathrm I_{60,\;}^{15^\circ}\mathrm I_{90,\;}^{15^\circ}\mathrm I_{120}^{15^\circ}\)</EquationSource> </InlineEquation>, respectively. A unit increase in rainfall intensity led to a higher increase in organic carbon flux in surface runoff (30.09–41.91 mg m−2) compared to sediment (0.148–0.286 mg m−2), while it reduced the flux in interflow by 7.22 mg m−2 on the 10° slope. For I ≤ 90, increasing the slope had similar effects, but at I120, steeper slopes reduced carbon loss across all pathways. Concurrent increases in rainfall intensity and slope synergistically increased surface runoff dissolved organic carbon (DOC) but antagonistically decreased interflow DOC, with the slope effect overriding, while sediment SOC was primarily increased by rainfall intensity. Conclusion SOC loss is path-dependent, with rainfall intensity dominating surface transport and slope gradient primarily governing interflow dynamics. This "pathway-driver" relationship rectifies the overlooked interflow role, directing targeted mitigation: prioritizing surface runoff interception in heavy rainfall and controlling the interflow "hidden pathway" on gentle slopes in low rainfall. Our findings provide a key theoretical basis for precise carbon loss control.

Simulated Rainfall Experiments Reveal the Selective Migration of Soil Organic Carbon in Relation to Rainfall Intensity and Slope

期刊论文
发表日期：

2026年4月17日

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Huanying Fang,
Mengqi Chang,
Shengsheng Xiao,
Yunhua Liao,
Junjie Huang,
Kun Qian

摘要

Purpose

Understanding how rainfall intensity and slope mediate soil organic carbon (SOC) transport is key to assessing carbon loss dynamics in sloped red-soil croplands, yet how carbon losses are partitioned among surface runoff, interflow, and sediment remains poorly quantified and understood.

Methods

A rainfall simulator was used to produce 90 min rainfall events of three intensities (60, 90, or 120 mm h⁻¹) for plots with two slope values (10° and 15°), with all possible combinations of rainfall intensity and slope tested (i.e., \(\mathrm I_{60,\;\;}^{10^\circ}\mathrm I_{90,\;}^{10^\circ}\;\mathrm I_{120,\;}^{10^\circ}\mathrm I_{60,\;}^{10^\circ}\mathrm I_{90,\;}^{15^\circ}\mathrm{and}\;\mathrm I_{120}^{15^\circ}\) ). Test plots were 3 m long, 1.5 m wide, and 0.6 m deep.

Results

The quantity of SOC migrating in the sediment (1,120–8,520 mg m⁻²), surface runoff (175.40–1,714.01 mg m⁻²), and interflow (1.61–92 mg m⁻²) was influenced by the rainfall intensity, slope, and their interaction (P < 0.05). The sediment to surface runoff to interflow ratio was 2:1 (excluding sediment SOC), 91:20:1, 2,236:450:1, 696:270:1, 1,079:246:1, and 1,047:246:1 for \(\mathrm I_{60,\;}^{10^\circ}\mathrm I_{90,\;}^{10^\circ}\mathrm I_{120,\;}^{10^\circ}\mathrm I_{60,\;}^{15^\circ}\mathrm I_{90,\;}^{15^\circ}\mathrm I_{120}^{15^\circ}\) , respectively. A unit increase in rainfall intensity led to a higher increase in organic carbon flux in surface runoff (30.09–41.91 mg m⁻²) compared to sediment (0.148–0.286 mg m⁻²), while it reduced the flux in interflow by 7.22 mg m⁻² on the 10° slope. For I ≤ 90, increasing the slope had similar effects, but at I₁₂₀, steeper slopes reduced carbon loss across all pathways. Concurrent increases in rainfall intensity and slope synergistically increased surface runoff dissolved organic carbon (DOC) but antagonistically decreased interflow DOC, with the slope effect overriding, while sediment SOC was primarily increased by rainfall intensity.

Conclusion

SOC loss is path-dependent, with rainfall intensity dominating surface transport and slope gradient primarily governing interflow dynamics. This "pathway-driver" relationship rectifies the overlooked interflow role, directing targeted mitigation: prioritizing surface runoff interception in heavy rainfall and controlling the interflow "hidden pathway" on gentle slopes in low rainfall. Our findings provide a key theoretical basis for precise carbon loss control.