Carbon dynamics in a Late Quaternary-age coastal limestone aquifer system undergoing saltwater intrusion
Carbon dynamics in a Late Quaternary-age coastal limestone aquifer system undergoing saltwater intrusion
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DOI：
10.1016/j.scitotenv.2017.06.094
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发表时间：
2017-12-31
影响因子：
9.8
通讯作者：
Post, Vincent E. A.
中科院分区：
文献类型：
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作者：
Bryan, Eliza;Meredith, Karina T.;Post, Vincent E. A.
本研究调查的无机和有机方面的碳循环在地下水中的整个淡水透镜和过渡带的碳酸盐岛屿含水层，并确定整个系统的碳的转化。我们确定了地下水中DIC和DOC的C-14和（13）C碳同位素值，并调查了整个含水层中DOC的组成。结合水化学和H-3的测量，地下水的化学演变，然后跟踪从非饱和区到更深的盐水区。数据显示了三种不同的水类型：淡水（F），过渡区1（T1）和过渡区2（T2）地下水。F和T1样品中的H-3值表明，这些地下水大多是现代的。C-14（DOC）值高于C-14（DIC）值，并与H-3值有很好的相关性。F和T1地下水地球化学以碳酸盐矿物重结晶反应为主，这些反应将死碳添加到地下水中。T2地下水较深，含盐，其特征是没有H-3，较低的C-14（DOC）值和不同的DOC组成，即较高比例的腐殖物质相对于总DOC。T2地下水可能是由于海水楔内水的缓慢循环，也可能是过去海平面高水位引起的老的残余海水。虽然需要进一步调查，以确定T2地下水的起源，这项研究已经确定了它们的出现，并表明，他们没有沿着相同的路径作为淡水地下水的演变。这项研究还表明，使用C-14和C-13碳同位素值DIC和DOC和DOC的组成，以及水化学和H-3测量的组合方法，可以提供宝贵的信息，在地下水系统中的碳的转化和淡水地下水补给的演变。(C)2017爱思唯尔B. V.保留所有权利。
This study investigates the inorganic and organic aspects of the carbon cycle in groundwaters throughout the freshwater lens and transition zone of a carbonate island aquifer and identifies the transformation of carbon throughout the system. We determined C-14 and(13)C carbon isotope values for both DIC and DOC in groundwaters, and investigated the composition of DOC throughout the aquifer. In combination with hydrochemical and H-3 measurements, the chemical evolution of groundwaters was then traced from the unsaturated zone to the deeper saline zone. The data revealed three distinct water types: Fresh (F), Transition zone 1 (T1) and Transition zone 2 (T2) groundwaters. The H-3 values in F and T1 samples indicate that these groundwaters are mostly modern. C-14(DOC) values are higher than C-14(DIC) values and are well correlated with H-3 values. F and T1 groundwater geo-chemistry is dominated by carbonate mineral recrystallisation reactions that add dead carbon to the groundwater. T2 groundwaters are deeper, saline and characterised by an absence of H-3, lower C-14(DOC) values and a different DOC composition, namely a higher proportion of Humic Substances relative to total DOC. The T2 groundwaters are suggested to result from either the slow circulation of water within the seawater wedge, or from old remnant seawater caused by past sea level highstands. While further investigations are required to identify the origin of the T2 groundwaters, this study has identified their occurrence and shown that they did not evolve along the same pathway as fresh groundwaters. This study has also shown that a combined approach using C-14 and C-13 carbon isotope values for both DIC and DOC and the composition of DOC, as well as hydrochemical and H-3 measurements, can provide invaluable information regarding the transformation of carbon in a groundwater system and the evolution of fresh groundwater recharge. (C) 2017 Elsevier B.V. All rights reserved.