基于13C、15N和C/N识别南岳小流域沉积有机质的来源

农业流域有机质流失造成水体富营养化和土地退化,不仅威胁水质和粮食安全,而且会导致温室气体排放等潜在环境问题。本研究用¹³C、¹⁵N和C/N作为指纹标志物,分析了南岳小流域出口沉积有机质的来源及其在林地、稻田和菜地等典型土地利用类型土壤的空间分布特征,并结合贝叶斯稳定同位素混合模型定量估算了各土地利用类型的贡献率。结果表明: δ¹³C具有显著的空间差异,沉积物有机质(-22.6‰±0.53‰)和林地土壤(-23.13‰±1.71‰)的δ¹³C显著高于稻田土壤(-25.24‰±1.4‰)。各土地利用类型土壤的δ¹⁵N差异不显著,沉积物的均值最大,为(4.37±0.83)‰,林地最小,为(2.38±1.97)‰;林地土壤的C/N均值最大,为16.66±7.18,稻田土壤的C/N均值最小,为11.95±0.92。贝叶斯稳定同位素混合模型结果显示,林地、稻田和菜地对流域出口沉积有机质的贡献率分别为19.6%、15.7%和64.7%;稻田和菜地作为农业用地的总贡献率为80.4%。说明农业用地土壤是南岳小流域沉积有机质的主要来源,可以通过优化农田管理措施有效控制流域养分流失。

Tracing the sources of sedimentary organic matter in Nanyue small watershed based on 13C, 15N and C/N

Losses of organic matter in agricultural watersheds result in eutrophication and land degra-dation, which not only threaten water quality and food security, but also lead to environmental problems such as the greenhouse gases emission. We used ¹³C, ¹⁵N and C/N as fingerprint markers to trace the sources of sedimentary organic matter at the outlet in the Nanyue small watershed. We analyzed the spatial distribution in watershed sedimentary organic matter and soils of typical land use types, including forest, paddy field, and vegetable fields. The Bayesian stable isotope mixing model was used to quantitatively estimate the contribution of different sources. The results showed that there was significant spatial variation of δ¹³C. The δ¹³C of sediment organic matter (-22.6‰±0.53‰) and forest soil (-23.13‰±1.71‰) was significantly higher than that of paddy soil (-25.24‰±1.4‰). The differences of δ¹⁵N among the sources were not significant, with sediment having the maximum (4.37±0.83)‰ and forest soil having the minimum (2.38±1.97)‰. Forest soil had the highest C/N of 16.66±7.18, while paddy soil had the lowest C/N of 11.95±0.92. The results of the Bayesian stable isotope mixture model showed that the contribution rates of forest land, paddy fields and vegetable fields to the organic matter deposited at the outlet in the watershed were 19.6%, 15.7%, and 64.7%, respectively. Paddy filed and vegetable field had a combined contribution rate of 80.4%. It was concluded that, soils of agricultural land were the main sources of organic matter deposited in the Nanyue small watershed, and that nutrient loss in the watershed would be effectively controlled by optimizing farmland management.