Salt marshes: An important coastal sink for dissolved uranium
Salt marshes: An important coastal sink for dissolved uranium
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DOI：
10.1016/0016-7037(96)00211-6
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发表时间：
1996-10-01
影响因子：
5
通讯作者：
Ferdelman, TG
中科院分区：
文献类型：
--
作者：
Church, TM;Sarin, MM;Ferdelman, TG
海洋铀的全球预算需要深海系统以外的另一个地球化学汇，而沿海环境可能拥有部分或全部这种缺失的汇。在以前的论文（沙林和教堂，1994年），我们已经表明，一些大的潮下河口季节性夏季汇在低盐度。在本文中，我们表明，潮间带盐沼甚至更强的汇在所有盐度，如果有点不同的原因，铀采样溶解和颗粒组分在几个潮汐周期和季节较低的特拉华州湾盐沼（金丝雀溪，刘易斯，特拉华州，美国），独特的是，在夏季，溶解铀是非保守的。此外，由于铀的提取是更高的潮汐和发生在整个盐度梯度，这一过程似乎与表面的植被高沼泽。我们假设，要么（1）铀清除过程中发生的潮汐混合和随之而来的絮凝腐殖酸和铁氧化物-有利于这一过程的存在下，磺酸盐络合物在盐沼腐殖物质，和铁共沉淀在其广泛的氧化还原循环在盐沼-或（2）铀提取发生在沼泽表面的盐沼表面沉积物的广泛洪水-有利于这一进程是在夏季盐沼表面的硫酸酸性的增加，可能会不稳定的四价铀物种的U（VI）。后一种选择是有利的条件，并选择性提取的沉积物相，其中铀被发现作为吸附和络合形式的抗坏血酸-柠檬酸和腐殖酸fractions.Mass平衡计算表明，在稳态条件下，近三分之二的铀提取的潮汐沃茨被保留在沉积物中，而三分之一的出口作为U-富集颗粒在退潮。对这种平衡的独立确认来自深埋铀的测量积累率。这代表了埋在地球化学反应表面以下的净存量，该表面负责铀的初始提取和重新分配到沉积物或潮汐输出相。从全球范围推断，仅盐沼或包括红树林在内的整个海洋湿地中的铀埋藏量就可能占海洋铀汇总量的至少10%，甚至可能高达50%，或者在特定区域的基础上，高达其海洋面积的50倍。
The global budget for marine uranium demands another geochemical sink other than deepsea systems, and the coastal environment may host some or all of this missing sink. In a previous paper (Sarin and Church, 1994), we have shown that some large subtidal estuaries are seasonal summer sinks at low salinities. In this paper, we show that intertidal salt marshes are even stronger sinks at all salinities, if for somewhat different reasons.Uranium was sampled in dissolved and particulate fractions over several tidal cycles and seasons for a lower Delaware Bay salt marsh (Canary Creek, Lewes, Delaware, USA), and uniquely, during summer months, the dissolved uranium is nonconservative. Moreover, because uranium extraction is greater on higher tides and occurs over the entire salinity gradient, this processing appears associated with surface of vegetated high marsh.We hypothesize that either (1) uranium scavenging occurs during the process of tidal mixing and attendant flocculation of humic acids and iron oxides-favoring this process is the presence of sulfonate complexes in salt marsh humic substances, and iron coprecipitation during its extensive redox cycling in the salt marsh-or (2) uranium extraction occurs at the marsh surface during extensive flooding of the salt marsh surface sediments-favoring this process is the increase in sulfuric acidity at the summer salt marsh surface that could destabilize the tetracarbonate species of U(VI). The latter option is favored conditions, and selective extraction of sediment phases where uranium is found as adsorbed and complexed forms in the ascorbate-citrate and humic acid fractions, respectively.Mass balance calculations show that under steady-state conditions, nearly two-thirds of the uranium extracted from tidal waters is retained in the sediments, while one-third is exported as U-enriched particles during ebbing tides. Independent confirmation of this balance comes from the measured accumulation rate of uranium buried at depth. This represents the net inventory buried below the geochemically reactive surface responsible for the initial extraction and redistribution of uranium onto sediment or tidally exported phases. Extrapolated globally, uranium burial in salt marshes alone or total marine wetlands including mangroves could comprise at least 10% and perhaps as much as 50% the total marine sink for uranium, or on an area specific basis, up to 50 times their marine areal extent.