Department of Natural Resource Sciences, McGill University, Sainte Anne-de-Bellevue H9X 3V9, Canada.
Science & Technology Branch, Environment and Climate Change Canada, Ottawa K1A 0H3, Canada.
Environ Int. 2021 Mar;148:106370. doi: 10.1016/j.envint.2020.106370. Epub 2021 Jan 18.
Top predators are used as indicators of contaminant trends across space and time. However, signals are integrated over complex food webs, and variation in diet may confound such signals. Trophic position, assessed by bulk δN, is widely used to infer the variation in diet relevant to contamination, yet a single variable cannot completely describe complex food webs. Thus, we examined relationships across three aquatic systems varying from a single species to a small food web using bulk values from four isotopes and 21 amino acid-specific values. Because variation in baseline ('source') δN can confound estimates of trophic position , we calculated trophic position from the difference between δN (δN for amino acids that change with trophic position) and δN (δN for amino acids that do not change with trophic position). Across all three systems, variation in δN explained over half of the variation in bulk δN, and stable isotope values that reflected the base of the food web (δC, δO, δS) predicted contaminants as well or better than δN-which was supported by a meta-analysis of other studies. In ospreys feeding in lakes, variation in δN across space created a spurious relationship between ΣDDT and apparent trophic position, and masked a relationship between ΣPCB and trophic position. In a seabird guild, changes in diet over time obscured temporal variation in contaminants over five decades. In Arctic fish and invertebrates, more accurate trophic magnification factors were calculated using δN. Thus, (1) using δN, instead of bulk δN, avoided incorrect conclusions and improved accuracy of trophic magnification factors necessary to assess risk to top predators; and (2) diet assessed with multiple spatial isotopes, rather than δN alone, was essential to understand patterns in contaminants across space, time and biological communities. Trophic position was most important for lipophilic 'legacy' contaminants (ΣDDT, ΣPCB) and habitat was most important for other contaminants (ΣPBDE, ΣPFAS, mercury). We argue that the use of amino acid-specific analysis of δN alongside 'non-trophic' isotopes should be a core feature of any study that examines the influence of trophic position on chemical pollution, as required for a chemical to be added to international conventions such as the Stockholm Convention.
顶级捕食者被用作跨时空污染物趋势的指标。然而，这些信号是在复杂的食物网中综合得到的，而饮食的变化可能会混淆这些信号。通过批量 δN 评估的营养位，广泛用于推断与污染相关的饮食变化，但单一变量并不能完全描述复杂的食物网。因此，我们使用来自四个同位素和 21 种氨基酸特异性值的批量值，研究了从单一物种到小食物网的三个水生系统的关系。由于基线（“源”）δN 的变化可能会混淆营养位的估计，因此我们从 δN（与营养位变化相关的氨基酸的 δN）和 δN（与营养位变化不相关的氨基酸的 δN）之间的差异计算营养位。在所有三个系统中，δN 的变化解释了批量 δN 变化的一半以上，反映食物网基础的稳定同位素值（δC、δO、δS）与 δN 一样或更好地预测了污染物，这得到了对其他研究的荟萃分析的支持。在湖泊中觅食的鱼鹰中，空间上 δN 的变化导致 ΣDDT 与表观营养位之间产生了虚假关系，并掩盖了 ΣPCB 与营养位之间的关系。在海鸟群体中，随着时间的推移，饮食的变化掩盖了五个十年期间污染物的时间变化。在北极鱼类和无脊椎动物中，使用 δN 计算出了更准确的营养放大因子。因此，（1）使用 δN 代替批量 δN 避免了错误的结论，并提高了评估顶级捕食者风险所需的营养放大因子的准确性；（2）使用多个空间同位素而不是单独的 δN 评估饮食对于理解污染物在空间、时间和生物群落中的分布至关重要。营养位对亲脂性“遗留”污染物（ΣDDT、ΣPCB）最重要，而栖息地对其他污染物（ΣPBDE、ΣPFAS、汞）最重要。我们认为，在任何研究中，使用 δN 的氨基酸特异性分析以及“非营养”同位素应该是检查营养位对化学污染影响的核心特征，这是根据《斯德哥尔摩公约》等国际公约添加化学物质所必需的。
