Development of a two-layer transport model in layered muddy-permeable marsh sediments using Ra-224-Th-228 disequilibria
Development of a two-layer transport model in layered muddy-permeable marsh sediments using Ra-224-Th-228 disequilibria
复制标题
利用 Ra-224-Th-228 不平衡建立层状泥质渗透性沼泽沉积物中的两层传输模型
DOI：
10.1002/lno.11143
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发表时间：
2019
影响因子：
4.5
通讯作者：
Moore Willard S
中科院分区：
文献类型：
--
作者：
Shi Xiangming;Benitez Nelson Claudia R;Cai Pinghe;He Lijian;Moore Willard S
地下渗流和沉积物-水界面是高浓度孔隙水溶质通过渗透性沉积物运移的重要通道。在这项研究中，我们利用镭-224/钍-228不平衡，检查溶质输运通过浅沉积物（深度< 30厘米）的潮汐沼泽地，北湾，南卡罗来纳州，在一个季节性周期。不同的224 Ra-228 Th不平衡模式表明，显着的孔隙水交换发生在直接穿过沉积物-水界面和在地下渗流深度。磷（P），铁（Fe）和锰（Mn）孔隙水浓度的时间变化也支持这种双层运输模型。跨界面的溶质运输的影响，季节性生物灌溉，最高的交换率发生在春末。溶解态Fe的界面通量在0.5 mmol m−2d− 1 ~ 134 mmol m−2d−1之间变化，可溶性活性磷酸盐（SRP）和溶解态Mn的界面通量分别在0.01 mmol m−2d− 1 ~ 0.72 mmol m−2d− 1和0.04 mmol m−2d− 1 ~ 2.7 mmol m−2d−1之间变化。渗漏全年发生，流体交换率与离潮沟的距离有关。通过渗流的SRP迁移范围为0.98 mmol m−2d− 1至5.0 mmol m−2d−1，比通过沉积物-水界面高一个数量级。深部的还原/氧化反应降低了深层孔隙水中微量金属的浓度，降低了Fe和Mn沿着渗流路径的迁移效率。虽然在潮汐循环过程中，相当一部分输出的溶质可能会返回沼泽沉积物，但我们的研究结果表明，富含有机物的沉积物为沿海生态系统提供了潜在的大量营养物质和微量元素来源。
Underground seepage and the sediment–water interface are important pathways for transporting concentrated pore water solutes through permeable sediments. In this study, we utilized radium‐224/thorium‐228 disequilibria to examine solute transport throughout shallow sediments (depth < 30 cm) of a tidal marshland, North Inlet, South Carolina, over a seasonal cycle. Distinct224Ra–228Th disequilibria patterns indicate that significant pore water exchange occurred both directly across the sediment–water interface and at depth as underground seepage. Temporal variations in phosphorus (P), iron (Fe), and manganese (Mn) pore water concentrations also support this two‐layer transport model. Solute transport across the interface was influenced by seasonal bioirrigation, with highest exchange rates occurring in the late spring. Interfacial flux of dissolved Fe ranged over two orders of magnitude, from 0.5 mmol m−2d−1to 134 mmol m−2d−1, and fluxes of soluble reactive phosphate (SRP) and dissolved Mn varied from 0.01 mmol m−2d−1to 0.72 mmol m−2d−1and from 0.04 mmol m−2d−1to 2.7 mmol m−2d−1, respectively. Seepage occurs year‐round, with fluid exchange rates related to the distance from the tidal creek. SRP transport via seepage ranged from 0.98 mmol m−2d−1to 5.0 mmol m−2d−1, one order of magnitude higher than across the sediment–water interface. Reduction/oxidation reactions at depth diminished trace metal concentrations in deep pore water, and lowered the transport efficiency of Fe and Mn along seepage paths. Although an appreciable fraction of exported solutes likely returns to marsh sediments during tidal circulation, our results indicate that organic‐rich sediments provide a potentially large source of nutrients and trace elements to the coastal ecosystem.