Sustainable Agriculture Sciences, Rothamsted Research, North Wyke, Okehampton, EX20 2SB, United Kingdom.
Sustainable Agriculture Sciences, Rothamsted Research, North Wyke, Okehampton, EX20 2SB, United Kingdom.
Water Res. 2022 Jun 1;216:118348. doi: 10.1016/j.watres.2022.118348. Epub 2022 Mar 22.
Excessive sediment loss degrades freshwater quality and is prone to further elevation and variable source contributions due to the combined effect of extreme rainfall and differing land uses. To quantify erosion and sediment source responses across scales, this study integrated work at both field and catchment scale for two hydrologically contrasting winters (2018-19 and 2019-20). Sediment load was estimated at the field scale (grassland-arable conversion system). Sediment source apportionment work was undertaken at the catchment scale (4.5 km) and used alkanes, and both free and bound fatty acid carbon isotope signatures as diagnostic fingerprints to distinguish sediment sources: arable, pasture, woodland and stream banks. Sediment source apportionment based on bound fatty acids revealed a substantial shift in contributions, from stream banks dominating (70 ± 5%) in winter 2018-19, to arable land dominating (52 ± 7%) in the extreme wet winter 2019-20. Increases in sediment contributions from arable (∼3.9 times) and pasture (∼2.4 times) land at the catchment outlet during the winter 2019-20 were consistent with elevated sediment losses monitored at the field scale which indicated that low-magnitude high frequency rainfall alone increased sediment loss even from pasture by 350%. In contrast, carbon isotope signatures of alkanes and free fatty acids consistently estimated stream banks as a dominant source (i.e., ∼36% and ∼70% respectively) for both winters regardless of prolonged rainfall in winter 2019-20. Beyond quantifying the shifts in field scale sediment load and catchment scale sediment sources due to the changes in rainfall patterns, our results demonstrate valuable insight into how the fate of biotracers in soil and sediment manifests in the δC values of homologues and, in turn, their role in information gain for estimating sediment source contributions. Discrepancies in the estimated sediment source contributions using different biotracers indicate that without a careful appreciation of their biogeochemical limitations, erroneous interpretation of sediment source contributions can undermine management strategies for delivering more sustainable and resilient agriculture.
过度的泥沙流失会降低淡水水质，并由于极端降雨和不同土地利用的综合影响，容易导致进一步的抬升和可变的源贡献。为了定量评估侵蚀和泥沙源在不同尺度上的响应，本研究将田间和流域尺度的工作相结合，对两个水文差异较大的冬季（2018-19 年和 2019-20 年）进行了研究。在田间尺度（草地-耕地转换系统）估算了泥沙负荷。在流域尺度（4.5 公里）进行了泥沙源分配工作，并使用烷烃以及游离和结合脂肪酸碳同位素特征作为诊断指纹，以区分泥沙源：耕地、牧场、林地和河岸。基于结合脂肪酸的泥沙源分配表明，贡献的变化很大，从 2018-19 年冬季河岸主导（70±5%），到 2019-20 年极端湿润冬季耕地主导（52±7%）。在 2019-20 年冬季，流域出口处来自耕地（增加约 3.9 倍）和牧场（增加约 2.4 倍）的泥沙贡献增加与在田间尺度监测到的泥沙流失增加一致，这表明即使是低幅度高频率降雨也会增加泥沙流失，甚至从牧场增加 350%。相比之下，烷烃和游离脂肪酸的碳同位素特征始终估计河岸是两个冬季的主要来源（即分别约为 36%和 70%），而不管 2019-20 年冬季的降雨持续时间如何。除了量化降雨模式变化导致的田间尺度泥沙负荷和流域尺度泥沙源的变化外，我们的结果还提供了有价值的见解，了解生物示踪剂在土壤和沉积物中的命运如何在同系物的 δC 值中表现出来，进而在估计泥沙源贡献方面发挥信息增益的作用。使用不同生物示踪剂估计的泥沙源贡献存在差异，这表明如果不仔细了解它们的生物地球化学限制，错误地解释泥沙源贡献可能会破坏实现更可持续和有弹性农业的管理策略。
