Identifying source soils in contemporary estuarine sediments: A new compound-specific isotope method
Identifying source soils in contemporary estuarine sediments: A new compound-specific isotope method
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DOI：
10.1007/s12237-007-9012-9
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发表时间：
2008-04-01
影响因子：
2.7
通讯作者：
Gibbs, M. M.
中科院分区：
文献类型：
--
作者：
Gibbs, M. M.
提出了一种用于识别和分配对河口沉积物有贡献的当代源土壤的新方法。该方法利用对来自植物的天然生物标志物（脂肪酸）进行特定化合物的同位素分析，将源土壤与单个集水区内的土地利用联系起来。为了识别和分配河口样本中的源土壤，该方法使用同位素混合模型IsoSource。然后对从IsoSource获得的可行比例进行调整，以考虑源土壤中有机碳的百分比。通过这种方法，对河口某一位置的每种源土壤贡献的估计不受微生物或生物地球化学过程中生物标志物降解的影响。识别依赖于对沉积物样本相对于来自集水区内不同土地利用的参考源土壤“库”的评估。潜在源的选择在地理上受到每种源土壤与所采集的沉积物地点之间自然联系要求的限制。一个案例研究使用这种方法绘制了在一个边缘有红树林的小河口的河三角洲上三种主要土地利用源土壤（牧场、原生林和松林）的分布。结果表明，源土壤的贡献在三角洲各地差异显著，而不是均匀分布，这引发了对仅取单个岩芯来描述河口沉积物特征的有效性的担忧。将源分配结果与土地利用数据相结合表明，河三角洲沉积物中松林土壤的平均贡献率几乎是集水区内松林土地利用面积百分比的三倍。此外，同位素特征表明，大部分松林土壤来自因皆伐而遭受侵蚀的面积小得多的区域，并且来自近期采伐的松林区域的土壤贡献可能是该集水区内相应土地利用面积的20倍之多。这是第一种能够在集水区尺度上按土地利用识别和分配对河口某一位置的沉积物有贡献的土壤来源的方法。结果以每种潜在源土壤比例贡献的在可定义范围内的“最佳估计”给出。使用这种方法获得的信息将有助于制定管理策略，以改变土地利用方式，减少河流的泥沙负荷，从而减轻对河口下游水生生态系统的影响。
A new method is proposed for the identification and apportionment of contemporary source soils contributing to estuarine sediments. The method uses compound-specific isotopic analysis of naturally occurring biomarkers (fatty acids) derived from plants to link source soils to land use within a single catchment. For identification and apportionment of source soils in the estuarine samples, the method uses the isotopic mixing model, IsoSource. The feasible proportions obtained from IsoSource are then scaled to allow for the percent organic carbon in the source soils. With this approach, the estimation of each source soil contribution to a location in the estuary is independent of any degradation of the biomarkers through microbial or biogeochemical processes. Identification relies on the evaluation of the sediment sample relative to a "library" of reference source soils from different land use within the catchment. Selection of potential sources is geographically constrained by the requirement for a natural linkage between each source soil and the sediment site sampled. A case study, using this method, mapped the distribution of three main land use source soils (pasture, native forest, and pine forest) across the river delta in a small estuary fringed with mangroves. Rather than being uniformly distributed, the results indicated that the source soil contributions varied markedly across the delta, raising concerns about the validity of taking single cores to characterize the sediments of an estuary. Coupling the source apportionment results with land use data indicated that the mean percent contribution of pine forest soil in the river delta sediments was almost three times greater than the percent land use area of pine forest in the catchment. Furthermore, isotopic signatures indicated that most of the pine forest soil came from the much smaller areas exposed to erosion by clear cut harvesting and that the soil contribution from recently harvested areas of pine forest could be as much as 20 times greater than that land use area in this catchment. This is the first method that can identify and apportion, by land use on a catchment scale, the sources of soil contributing to the sediment at a location of an estuary. The results are given as a "best estimate", within definable limits, of the proportional contribution of each potential source soil. Information obtained using this method will allow development of management strategies to alter land use practices to reduce the sediment load to rivers, and thus, the impact on the aquatic ecosystem downstream in estuaries.