School of Fisheries, Aquaculture, and Aquatic Sciences, Auburn University , Auburn, Alabama 36849, United States.
Department of Oceanography, University of Hawaii , Manoa, 1000 Pope Road, Honolulu, Hawaii 96822, United States.
Environ Sci Technol. 2017 Dec 5;51(23):13976-13984. doi: 10.1021/acs.est.7b04893. Epub 2017 Nov 22.
The complex biogeochemical cycle of Hg makes identifying primary sources of fish tissue Hg problematic. To identify sources and provide insight into this cycle, we combined carbon (δC), nitrogen amino acid (δN), and Hg isotope (ΔHg, ΔHg, δHg) data for six species of Hawaiian marine bottomfish. Results from these isotopic systems identified individuals within species that likely fed from separate food webs. Terrestrial freshwater inputs to coastal sediments were identified as the primary source of tissue Hg in the jack species, Caranx ignobilis, which inhabit shallow marine ecosystems. Thus, coastal C. ignobilis were a biological vector transporting Hg from freshwater environments into marine ecosystems. Depth profiles of Hg isotopic compositions for bottomfish (excludung C. ignobilis) were similar, but not identical, to profiles for open-ocean pelagic fishes, suggesting that in both settings inorganic Hg, which was ultimately transformed to monomethylmercury (MeHg) and bioaccumulated, was dominantly from a single source. However, differences between pelagic fish and bottomfish profiles were attributable to mass-dependent fractionation in the benthos prior to incorporation into the food web. Results also confirmed that bottomfish relied, at least in part, on a benthic food web and identified the incorporation of deeper water oceanic MeHg sources into deeper water sediments prior to food web uptake and transfer.
汞的复杂生物地球化学循环使得确定鱼类组织中汞的主要来源变得很困难。为了确定来源并深入了解这一循环，我们结合了六种夏威夷海洋底层鱼类的碳（δC）、氮氨基酸（δN）和汞同位素（ΔHg、ΔHg、δHg）数据。这些同位素系统的结果鉴定出了同一物种内可能来自不同食物网的个体。沿海沉积物中陆地淡水的输入被确定为栖息在浅海生态系统中的杰克鱼（Caranx ignobilis）组织中汞的主要来源。因此，沿海的 C. ignobilis 是一种将汞从淡水环境输送到海洋生态系统的生物载体。底层鱼类（不包括 C. ignobilis）的汞同位素组成深度剖面与开阔洋区浮游鱼类的剖面相似，但并不完全相同，这表明在这两种环境中，最终转化为甲基汞（MeHg）并生物累积的无机汞主要来自单一来源。然而，浮游鱼类和底层鱼类之间的差异归因于海底在进入食物网之前的质量依赖性分馏。结果还证实，底层鱼类至少部分依赖底栖食物网，并确定了在食物链摄取和转移之前，更深层海洋的 MeHg 源被纳入更深层的海底沉积物。
