Soil erosion and soil organic carbon (SOC) loss are not always linked linearly because SOC‐rich topsoil is eroded at the initial stages of degradation, while horizons with lower SOC content are eroded later, but often at higher rates. Small, silted‐up farm reservoirs potentially document this change during the period of sediment accumulation. This study tests the specific potential of small farm reservoir sediments from the South African Karoo to reconstruct 20th century SOC and total nitrogen (TN) change in rangeland soils. Five reservoir sediment profiles were sampled and texture, total organic carbon (TOC), TN and 137Cs of the samples were analyzed and compared. The results show that there clearly distinguishable flood couplets have been preserved in the sediment, illustrating their suitability for the chronological reconstruction of soil erosion and SOC. With one exception, the older sediments contain more TOC and TN than the younger ones. The TOC changed mostly in earlier than later stages of deposition, which is indicative of soil degradation early after the construction of the dams in the 1920s and 1930s. These distinct changes illustrate that the small reservoir sediments have the potential to reconstruct the impact of land‐use and associated soil erosion on SOC change in rangelands. Their analysis can therefore contribute to a better understanding of the land‐use associated changes of the global carbon cycle during the 20th century.

中文翻译：

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从小型水库沉积物中重建 20 世纪牧场土壤有机碳侵蚀的潜力


土壤侵蚀和土壤有机碳 （SOC） 损失并不总是线性相关的，因为富含 SOC 的表层土壤在退化的初始阶段被侵蚀，而 SOC 含量较低的地层则被侵蚀得更晚，但通常侵蚀速度更高。小型、淤塞的农场水库可能在沉积物积累期间记录了这种变化。本研究测试了南非 Karoo 的小型农场水库沉积物在重建 20 世纪牧场土壤 SOC 和总氮 （TN） 变化方面的特定潜力。对 5 个储层沉积物剖面进行采样，并对样品的质地、总有机碳 （TOC） 、TN 和 137Cs 进行分析和比较。结果表明，沉积物中保留了明显可区分的洪水对联，说明它们适用于土壤侵蚀和 SOC 的时间重建。除了一个例外，较老的沉积物比较年轻的沉积物含有更多的 TOC 和 TN。TOC 主要在沉积的早期阶段而不是晚期阶段发生变化，这表明 1920 年代和 1930 年代大坝建造后早期的土壤退化。这些明显的变化表明，小型储层沉积物有可能重建土地利用和相关土壤侵蚀对牧场土壤有机碳变化的影响。因此，他们的分析有助于更好地了解 20 世纪全球碳循环中与土地利用相关的变化。