Organic tracers (bulk δ¹³C and δ¹⁵N) are being increasingly used in sediment/particulate organic carbon source apportionment studies at the catchment scale to support sustainable land management decisions. Here, the use of these isotopic tracers in sediment fingerprinting depends on the critical assumption that δ¹³C and δ¹⁵N values remain conservative during the sediment delivery continuum. Such assumption, however, requires critical evaluation, especially since standard tracer conservation tests applied in conjunction with catchment scale studies are prone to masking potential issues at smaller spatial scales including the field scale. Against this background, our study evaluated the subtle isotopic shift associated with sediment redistribution to edge-of-field and assessed the impact on sediment source apportionment. In a C₃-grass dominated study field, δ¹³C and δ¹⁵N values exhibited differences (i.e., Δ¹³C = 1.4 ± 0.7‰ and Δ¹⁵N = 0.4 ± 0.4‰) between soil depths of 0–5 cm and 5–10 cm. Sampled sediments at the edge-of-field flume had higher δ¹³C values than the 0–5 cm soil layer; i.e., Δ¹³C values were 0.3 ± 0.4‰ and 0.8 ± 0.4‰ for suspended and deposited (materials deposited in a basket downstream of a flume) sediment, respectively. In contrast, δ¹⁵N values increased in suspended (Δ¹⁵N = 0. 8 ± 0.6‰) but decreased (Δ¹⁵N = − 0.4 ± 0.5‰) in deposited sediment, compared to the 0–5 cm soil layer, suggesting that the N isotopes can respond differently in edge-of-field sediment types. Although current fingerprinting work tends to not take explicit account of organic tracer alteration during transport or after deposition, our results demonstrate that correcting sediment δ¹³C and δ ¹⁵N values for tracer alteration in a Bayesian un-mixing model generated robust and reliable estimates of source contributions to both target sediment types. We therefore recommend taking account of the subtle but consistently altered δ¹³C and δ ¹⁵N values along the sediment cascade in un-mixing modelling to help better discriminate sources and to improve un-mixing model estimates at the catchment scale.

有机示踪剂（大量δ ¹³ C 和δ ¹⁵ N）越来越多地用于流域尺度的沉积物/颗粒有机碳源分配研究，以支持可持续的土地管理决策。在这里，这些同位素示踪剂在沉积物指纹识别中的使用取决于δ ¹³ C 和δ ¹⁵N 值在沉积物输送连续过程中保持保守。然而，这种假设需要严格的评估，特别是因为与集水区规模研究结合应用的标准示踪剂保护测试容易掩盖包括田间规模在内的较小空间尺度上的潜在问题。在此背景下，我们的研究评估了与沉积物重新分布到场地边缘相关的细微同位素变化，并评估了对沉积物源分配的影响。在以C _{3 -}草为主的研究领域，δ ¹³ C 和δ ¹⁵ N 值表现出差异（即，Δ ¹³ C = 1.4 ± 0.7‰和Δ ¹⁵N = 0.4 ± 0.4‰) 在 0-5 厘米和 5-10 厘米的土壤深度之间。田边水槽采样沉积物的δ ¹³ C 值高于 0-5 cm 土层；即，对于悬浮和沉积（沉积在水槽下游篮子中的材料）沉积物，Δ ¹³ C 值分别为 0.3 ± 0.4‰ 和 0.8 ± 0.4‰。相比之下，悬浮液中δ ¹⁵ N 值增加（Δ ¹⁵ N = 0. 8 ± 0.6‰）但下降（Δ ¹⁵N = − 0.4 ± 0.5‰) 在沉积沉积物中，与 0-5 cm 土层相比，这表明 N 同位素在田间沉积物类型中的响应不同。尽管目前的指纹识别工作往往没有明确考虑运输过程中或沉积后的有机示踪剂变化，但我们的结果表明，在贝叶斯解混合模型中校正沉积物δ ¹³ C 和δ ¹⁵ N 的示踪剂变化值产生了稳健可靠的估计源对两种目标沉积物类型的贡献。因此，我们建议考虑微妙但持续变化的δ ¹³ C 和δ ¹⁵在非混合建模中沿沉积物级联的 N 值有助于更好地区分来源并改进流域尺度的非混合模型估计。