Variation in Terrestrial and Aquatic Sources of Methylmercury in Stream Predators as Revealed by Stable Mercury Isotopes
Variation in Terrestrial and Aquatic Sources of Methylmercury in Stream Predators as Revealed by Stable Mercury Isotopes
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稳定汞同位素揭示溪流捕食者中陆地和水生甲基汞来源的变化
DOI：
10.1021/es500517s
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发表时间：
2014
影响因子：
11.4
通讯作者：
Power, Mary E.
中科院分区：
文献类型：
--
作者：
Tsui, Martin Tsz-Ki;Blum, Joel D.;Finlay, Jacques C.;Balogh, Steven J.;Nollet, Yabing H.;Palen, Wendy J.;Power, Mary E.
汞（Hg）广泛分布于环境中，其有机形式甲基汞（MeHg）可以在水生和陆生食物网中广泛地进行生物积累和生物放大。生物体中甲基汞的浓度变化很大，人们对天然食物网中的甲基汞来源往往不太了解。本研究在加州北部南福克鳗鱼河源头的森林流域，检测了底栖无脊椎动物、幼年虹鳟（Oncorhynchus mykiss）、水踏鱼（Gerris remigis）以及食肉陆生无脊椎动物中MeHg的稳定同位素比率（质量依赖分异，δ202HgMeHg；和质量独立分异，Δ199HgMeHg）。在整个采样点，δ202HgMeHg（由于MeHg光降解的影响进行校正后）在底栖动物（中位数= - 1.40‰，范围为- 2.34 ~ - 0.78‰，样品总数= 29）和陆生无脊椎动物（中位数= +0.51‰，范围为- 0.37 ~ +1.40‰，样品总数= 9）之间差异显著，但在Δ199HgMeHg上两组间差异不显著。钢头鳟鱼（52条单独的鱼）的甲基汞主要来自水生，上游地区有少数例外（例如，在一条支流中收集的1条鱼的甲基汞来源纯粹是陆地，4条鱼的甲基汞来源混合是水生和陆地）。水黾（7个汇集的样本）在整个水源段主要从陆地来源获得甲基汞。这些数据表明，直接的陆地补贴（例如，陆生无脊椎动物落入水中）对源头溪流中的一些溪流捕食者可能很重要，并且可能是陆地来源的甲基汞（例如，森林、大气源内的原位甲基化）向水生生态系统转移的重要手段。此外，这些研究结果表明，陆地补贴可以增强消费者在水中甲基汞含量非常低的水源溪流中的甲基汞生物积累。
Mercury (Hg) is widely distributed in the environment, and its organic form, methylmercury (MeHg), can extensively bioaccumulate and biomagnify in aquatic and terrestrial food webs. Concentrations of MeHg in organisms are highly variable, and the sources in natural food webs are often not well understood. This study examined stable isotope ratios of MeHg (mass-dependent fractionation, as δ202HgMeHg; and mass-independent fractionation, as Δ199HgMeHg) in benthic invertebrates, juvenile steelhead trout (Oncorhynchus mykiss), and water striders (Gerris remigis) along a stream productivity gradient, as well as carnivorous terrestrial invertebrates, in a forested watershed at the headwater of South Fork Eel River in northern California. Throughout the sampling sites, δ202HgMeHg(after correction due to the effect of MeHg photodegradation) was significantly different between benthic (median = −1.40‰; range, −2.34 to −0.78‰; total number of samples = 29) and terrestrial invertebrates (median = +0.51‰; range, −0.37 to +1.40‰; total number of samples = 9), but no major difference between these two groups was found for Δ199HgMeHg. Steelhead trout (52 individual fishes) have MeHg of predominantly aquatic origins, with a few exceptions at the upstream locations (e.g., 1 fish collected in a tributary had a purely terrestrial MeHg source and 4 fishes had mixed aquatic and terrestrial MeHg sources). Water striders (seven pooled samples) derive MeHg largely from terrestrial sources throughout headwater sections. These data suggest that direct terrestrial subsidy (e.g., terrestrial invertebrates falling into water) can be important for some stream predators in headwater streams and could represent an important means of transfer of terrestrially derived MeHg (e.g., in situ methylation within forests, atmospheric sources) to aquatic ecosystems. Moreover, these findings show that terrestrial subsidies can enhance MeHg bioaccumulation of consumers in headwater streams where aqueous MeHg levels are very low.