Molecular Eco-Geochemistry (MEG) Laboratory, Department of Geological Sciences, The University of Alabama, Tuscaloosa, AL 35487, USA.
Geological Survey of Alabama, Tuscaloosa, AL, USA.
Sci Total Environ. 2022 Sep 10;838(Pt 1):155779. doi: 10.1016/j.scitotenv.2022.155779. Epub 2022 May 10.
Hydrocarbons in estuarine sediments provide information on sources of sedimentary organic matter (OM), and they are thus useful for tracing natural and anthropogenic OM inputs to the estuary. Here, we assessed the amounts, compositions and sources of natural and anthropogenic hydrocarbons from the sediments of a large, ecologically important estuary, Mobile Bay in Southeast USA. TOC/TN ratios and δC of organic carbon suggest that the bulk natural OM was sourced from marine phytoplankton and bacteria mixed with marsh and terrigenous C3 plants. Normal alkanes show high proportions of long-chain compounds with a high Carbon Preference Index, indicating the importance of C3 plants-derived OM in Mobile Bay. High concentrations of biogenic hopanes and perylene indicate microbial sources and degradation played an important role in shaping OM compositions. Anthropogenic hydrocarbons, αβ-hopanes and polycyclic aromatic hydrocarbons (PAHs), were widely detected in Mobile Bay sediments. The source diagnostic ratios of hopanes and steranes suggest they were sourced from coal and diesel combustions. The source diagnostic ratios of PAHs, together with a positive correlation between PAHs and total mercury, suggests that PAHs originated primarily from coal combustion. We proposed two ratios, αβ-hopanes/(ββ-hopanes+hopenes) and 16 PAHs/perylene, to evaluate anthropogenic versus natural contributions of hydrocarbons. These ratios were higher in the western estuary than in the eastern estuary, suggesting elevated anthropogenic hydrocarbon inputs to the western estuary. Correspondingly, the toxic equivalent quantity (TEQ) of PAHs showed a higher ecological risk for the western estuary. This spatially uneven distribution of hydrocarbon pollutants can be attributed to more concentrated urban and industrial areas on the western shore, suggesting the importance of adjacent pollution sources. Collectively, our results provide new insights into the origins and dynamics of natural and anthropogenic OM and highlight the significance of coal combustion in contributing hydrocarbon pollutants in Mobile Bay sediments.
在河口沉积物中，碳氢化合物提供了有关沉积有机质（OM）来源的信息，因此对于追踪河口自然和人为 OM 输入非常有用。在这里，我们评估了来自美国东南部大型生态重要河口莫比尔湾沉积物中的自然和人为碳氢化合物的数量、组成和来源。TOC/TN 比和有机碳的 δC 表明，大部分自然 OM 来自海洋浮游植物和细菌，与沼泽和陆源 C3 植物混合。正构烷烃显示出长链化合物的高比例和高碳偏好指数，表明 C3 植物衍生的 OM 在莫比尔湾中的重要性。生物成因藿烷和并苯的高浓度表明微生物源和降解在塑造 OM 组成方面发挥了重要作用。在莫比尔湾沉积物中广泛检测到人为碳氢化合物、αβ-藿烷和多环芳烃（PAHs）。藿烷和甾烷的源诊断比表明它们来自煤和柴油燃烧。PAHs 的源诊断比，以及 PAHs 与总汞之间的正相关关系，表明 PAHs 主要来自煤燃烧。我们提出了两个比值，αβ-藿烷/（ββ-藿烷+藿烯）和 16 种 PAHs/并苯，以评估碳氢化合物的人为与自然贡献。这些比值在西部河口高于东部河口，表明西部河口人为碳氢化合物输入增加。相应地，PAHs 的毒性等效量（TEQ）显示出西部河口更高的生态风险。这种碳氢化合物污染物的空间不均匀分布可归因于西部海岸更集中的城市和工业区域，这表明相邻污染源的重要性。总的来说，我们的研究结果为自然和人为 OM 的起源和动态提供了新的见解，并强调了煤燃烧在莫比尔湾沉积物中碳氢化合物污染物形成中的重要性。
