Incorporating concentration dependence in stable isotope mixing models
Incorporating concentration dependence in stable isotope mixing models
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DOI：
10.1007/s004420100786
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发表时间：
2002-01-01
期刊：
影响因子：
2.7
通讯作者：
Koch, PL
中科院分区：
文献类型：
--
作者：
Phillips, DL;Koch, PL
稳定同位素常被用作天然标记，以量化多种来源对混合物的贡献。例如，碳和氮同位素特征可用于确定消费者饮食中三种食物来源的比例。标准的双同位素、三源线性混合模型假定，一种来源对混合物的比例贡献对于两种元素（例如，碳、氮）是相同的。如果所有来源的浓度相似，这可能是一个合理的假设。然而，一种来源往往在一种元素（例如，氮）上特别丰富或贫乏，这从逻辑上导致该来源对混合物中该元素相对于另一种元素（例如，碳）的贡献成比例地增加或减少。我们开发了一种浓度加权线性混合模型，该模型假定对于每种元素，一种来源的贡献与贡献质量乘以该来源中的元素浓度成正比。该模型针对两种元素和三种来源进行了概述，但可推广到n种元素和n + 1种来源。对三种来源的碳和氮进行的敏感性分析表明，仅改变一种来源的氮浓度对质量、碳和氮的估计来源贡献有很大且不同的影响。对以鲑鱼、驼鹿和贫氮植物为食的熊的案例研究也是如此。在这个例子中，浓度加权模型估计的鲑鱼生物量贡献明显小于标准模型的估计值。将该模型应用于以鲑鱼、瘦牛肉和富碳、贫氮牛肉脂肪为食的圈养水貂的圈养喂养研究时，非常接近地重现了已知的饮食比例，而标准模型未能得出一组正的来源比例。每当来源之间的元素浓度差异很大时，建议使用这种浓度加权模型，这可能发生在稳定同位素分析的各种生态和地球化学应用中。除了饮食和食物网研究之外，可能的例子包括对土壤、植物或水体中水源的稳定同位素分析；土壤或海洋系统的地质来源、分解和土壤有机质动态以及追踪动物迁徙模式。用于执行该模型计算的电子表格可在http://www.epa.gov/wed/pages/models.htm获取。
Stable isotopes are often used as natural labels to quantify the contributions of multiple sources to a mixture. For example, C and N isotopic signatures can be used to determine the fraction of three food sources in a consumer's diet. The standard dual isotope, three source linear mixing model assumes that the proportional contribution of a source to a mixture is the same for both elements (e.g., C, N). This may be a reasonable assumption if the concentrations are similar among all sources. However, one source is often particularly rich or poor in one element (e.g., N), which logically leads to a proportionate increase or decrease in the contribution of that source to the mixture for that element relative to the other element (e.g., C). We have developed a concentration-weighted linear mixing model, which assumes that for each element, a source's contribution is proportional to the contributed mass times the elemental concentration in that source. The model is outlined for two elements and three sources, but can be generalized to n elements and n+1 sources. Sensitivity analyses for C and N in three sources indicated that varying the N concentration of just one source had large and differing effects on the estimated source contributions of mass, C, and N. The same was true for a case study of bears feeding on salmon, moose, and N-poor plants. In this example, the estimated biomass contribution of salmon from the concentration-weighted model was markedly less than the standard model estimate. Application of the model to a captive feeding study of captive mink fed on salmon, lean beef, and C-rich, N-poor beef fat reproduced very closely the known dietary proportions, whereas the standard model failed to yield a set of positive source proportions. Use of this concentration-weighted model is recommended whenever the elemental concentrations vary substantially among the Sources'. which may occur in a variety of ecological and geochemical applications of stable isotope analysis. Possible examples besides dietary and food web Studies include stable isotope analysis of water Sources in soils, plants, or water bodies; geological Sources for soils or marine systems, decomposition and soil organic matter dynamics. and tracing animal migration patterns. A spreadsheet for performing the calculations for this model is available at http://www.epa.gov/wed/pages/models.htm.