An assessment of assumptions and uncertainty in deuterium-based estimates of terrestrial subsidies to aquatic consumers
An assessment of assumptions and uncertainty in deuterium-based estimates of terrestrial subsidies to aquatic consumers
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DOI：
10.1002/ecy.2211
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发表时间：
2018-05-01
期刊：
影响因子：
4.8
通讯作者：
Schindler, Daniel E.
中科院分区：
文献类型：
--
作者：
Brett, Michael T.;Holtgrieve, Gordon W.;Schindler, Daniel E.
由于陆地和水生初级生产者之间的价值差异很大，组织中的氘比率 (H-2/H-1) 通常用于估算陆地对水生消费者的补贴。然而，基于氘的陆地资源同化定量分析高度依赖于几个定义不明确的假设。我们探讨了这些估计值对环境水对消费者氘含量 (omega) 和藻类光合氢歧视 (epsilon(H)) 贡献的假设的敏感性。我们还测试了基于 C-13/C-12 和 H-2/H-1 的陆地资源同化估计是否给出了类似的结果。直接估计环境水对消费者组织 H-2/H-1 比例贡献的 12 项实验的平均值为 0.27 +/- 0.11（平均值 +/- SD），无脊椎动物和鱼类的值相似。相反，在使用 H-2/H-1 来描述水生食物网特征的 28 项实地研究中，除了一项之外，所有研究的假设值都低于我们目前的最佳估计值，通常要低得多。对最近四个案例研究的原始数据的重新分析表明，计算出的陆地对水生消费者的贡献对这一假设极其敏感。当使用作者最初的假设（即 omega = 0.16 +/- 0.05）时，陆地资源对水生消费者的估计比例贡献（theta(T)）平均为 29 +/- 17%，而当使用 omega = 0.27 时，异地资源的平均估计同化近似于 0.00。已发表的微藻光合氢歧视值的汇编平均 epsilon(H) = -150 +/- 27 ppm (SD, n = 99)，敏感性分析表明这些计算的结果也受到 epsilon(H) 不确定性的强烈影响。 C-13/C-12 和基于 H-2/H-1 的地面补贴估计之间没有统计关联（r = -0.12，n = 274）。该分析表明，基于氘的陆地资源同化估计中的假设影响很大，但约束很弱；因此，必须仔细评估并彻底报告这些假设对计算产出的影响。由于基于氘的分析固有的高度不确定的假设，我们敦促在使用这种方法来估计对水生生态系统消费者的陆地补贴时更加谨慎。
The deuterium ratio (H-2/H-1) in tissue is often used to estimate terrestrial subsidies to aquatic consumers because of strongly differentiated values between terrestrial and aquatic primary producers. However, quantitative deuterium-based analyses of terrestrial resource assimilation are highly dependent on several poorly defined assumptions. We explored the sensitivity of these estimates to assumptions regarding environmental water contributions to consumer deuterium content (omega) and algal photosynthetic hydrogen discrimination (epsilon(H)). We also tested whether C-13/C-12 and H-2/H-1-based estimates of terrestrial resource assimilation give similar outcomes. The average of the 12 experiments that have directly estimated proportional contributions of environmental water to consumer tissue H-2/H-1 was 0.27 +/- 0.11 (mean +/- SD), with similar values for invertebrates and fish. Conversely, of the 28 field studies that have used H-2/H-1 to characterize aquatic food webs, all but one assume a value that is less than our current best estimate, usually substantially less. A reanalysis of the raw data from four recent case studies indicates the calculated terrestrial contribution to aquatic consumers is extremely sensitive to this assumption. When the authors' original assumptions were used (i.e., omega = 0.16 +/- 0.05), the estimated proportional contribution of terrestrial resources to aquatic consumers (theta(T)) averaged 29 +/- 17%, and when omega = 0.27 was used the average estimated assimilation of allochthonous resources was approximate to 0.00. A compilation of published photosynthetic hydrogen discrimination values for microalgae averaged epsilon(H) = -150 +/- 27 parts per thousand (SD, n = 99), and a sensitivity analysis showed the outcomes of these calculations were also strongly influenced by uncertainty in epsilon(H). There was no statistical association between C-13/C-12 and H-2/H-1-based estimates of terrestrial subsidies (r = -0.12, n = 274). This analysis indicates that the assumptions in deuterium-based estimates of terrestrial resource assimilation are highly influential but poorly constrained; therefore, the impact of these assumptions on calculated outputs must be carefully assessed and thoroughly reported. Due to the highly uncertain assumptions inherent in deuterium-based analyses, we urge much more caution when using this approach to estimate terrestrial subsidies to consumers in aquatic ecosystems.