Soil carbon dioxide dynamics in deep profiles under erosional and depositional conditions on the Chinese Loess Plateau

Soil erosion, a major process in soil degradation, significantly influences carbon emissions and the CO₂ exchange between the atmosphere and soil, affecting the redistribution of soil organic carbon (SOC) and soil inorganic carbon (SIC). This, in turn, has important implications for the global carbon cycle and climate change. Understanding soil carbon dynamics under different erosion and deposition conditions is essential for managing carbon stocks. This study investigates the effects of erosion and deposition on SOC and SIC distribution and their contribution to CO₂ flux across soil profiles (0-200 cm depth) at three check dams in the Loess Plateau, China. The results show that soil erosion reduces carbon stocks, with SOC decreasing by 13.0% and SIC by 2.1% at depositional sites compared to erosional sites. CO₂ fluxes at erosional sites are significantly lower than at depositional sites, with fluxes peaking in August during the growing season. Seasonal variations in CO₂ flux are consistent across erosion environments. Correlation analysis indicates that at erosional sites, CO₂ flux is strongly correlated with soil temperature, SOC, SIC, and pH, while at depositional sites, it is more strongly correlated with soil temperature and moisture content. These findings highlight differing environmental controls on CO₂ flux between erosion and deposition sites. Additionally, δ¹³C values of CO₂ emissions were more negative at erosion sites, reflecting a higher contribution from SOC, while at deposition sites, the values were less negative, indicating a stronger influence of SIC, especially in deeper soil layers. The study emphasizes that SOC and SIC play crucial roles in influencing soil CO₂ flux, with the dynamics of carbon redistribution under erosion processes significantly affecting carbon cycling and storage. These results underline the need for site-specific land management strategies to mitigate soil carbon loss and enhance soil health in erosion-prone areas.土壤侵蚀作为土壤退化的核心过程之一，可显著影响碳排放及大气与土壤间的二氧化碳交换，进而调控土壤有机碳（SOC）与土壤无机碳（SIC）的再分布。该过程继而对全球碳循环与气候变化产生重要影响。明晰不同侵蚀与沉积条件下的土壤碳动态，对碳库管理至关重要。本研究针对中国黄土高原3座谷坊（check dams），探究了侵蚀与沉积作用对SOC与SIC分布的影响，及其对0-200 cm深度土壤剖面内二氧化碳通量（CO₂ flux）的贡献。研究结果显示，土壤侵蚀会降低碳库储量：相较于侵蚀位点，沉积位点的SOC与SIC分别下降13.0%与2.1%。侵蚀位点的二氧化碳通量显著低于沉积位点，且通量在生长季的8月达到峰值。不同侵蚀环境下的二氧化碳通量季节变化规律一致。相关性分析表明，在侵蚀位点，二氧化碳通量与土壤温度、SOC、SIC及pH值呈显著相关；而在沉积位点，通量与土壤温度及土壤含水量的相关性更强。上述研究结果凸显了侵蚀与沉积位点间二氧化碳通量受环境调控机制的差异。此外，侵蚀位点的二氧化碳排放δ¹³C值更负，反映出SOC的贡献占比更高；而沉积位点的δ¹³C值负值更小，表明SIC的影响更强，尤其是在深层土壤中。本研究强调，SOC与SIC在调控土壤二氧化碳通量中发挥关键作用，侵蚀过程下的碳再分布动态可显著影响碳循环与碳储存。上述结果凸显了针对特定区域制定土地管理策略的必要性，以减缓易侵蚀区域的土壤碳损失并提升土壤健康水平。