Solute transport into the Jiulong River estuary via pore water exchange and submarine groundwater discharge: New insights from 224Ra/228Th disequilibrium
Solute transport into the Jiulong River estuary via pore water exchange and submarine groundwater discharge: New insights from 224Ra/228Th disequilibrium
复制标题
通过孔隙水交换和海底地下水排放溶质进入九龙江口：224Ra/228Th不平衡的新见解
DOI：
10.1016/j.gca.2016.11.002
复制
发表时间：
2017-02-01
影响因子：
5
通讯作者：
Wang, Guizhi
中科院分区：
文献类型：
--
作者：
Hong, Qingquan;Cai, Pinghe;Wang, Guizhi
孔隙水交换（PEX）和海底地下水排泄（SGD）是溶质从海底向近海迁移的两种机制。然而，它们的相对重要性仍有待评估。在这项研究中，我们追求最近开发的Ra-224/Th-228不平衡的方法来量化的PEX通量Ra-224进入九龙江河口，中国。通过建立完整的Ra-224水柱质量平衡，我们可以把各种源项，即。例如，SGD，扩散和平流孔隙水流量（PEX），和河流输入在一个单一的背景下。这导致了第一次定量评估的相对重要性的PEX与SGD在交付的溶质进入河口。我们在九龙江口进行了两次调查：一次是2014年1月（冬季调查），另一次是2014年8月（夏季调查）。借助沉积柱中Ra-224的一维质量平衡模型，我们证明了Ra-224的PEX通量在时间和空间上都是高度可变的，在我们的研究区域可以变化1-2个数量级。此外，我们确定了Ra-224为基础的灌溉率和234 Th为基础的泥沙混合率之间的强相关性。我们的研究结果突出了灌溉作为主要的PEX过程中溶质迁移通过沉积物-水界面。在冬季和夏季调查期间，Ra-224进入九龙江口的总PEX通量（以10（10）dpm d（-1）计）分别为22.3 +/- 3.0和33.7 +/- 5.5。相比之下，Ra-224的总SGD通量（以10（10）dpm d（-1）计）在相应季节分别为11.3 +/- 8.6和49.5 +/- 16.3。将Ra-224的PEX通量乘以沉积物-水界面组分/Ra-224浓度梯度的比值，定量计算了九龙江河口溶解无机碳（DIC）和营养盐（NH 4+、NO3-和H4 SiO 4）的PEX通量。与此同时，通过SGD的DIC和营养物的净输出是通过将Ra-224的SGD通量乘以该区域周围SGD端元中的DIC（营养物）/Ra-224比率来估计的。我们的研究结果表明，在河口的PEX驱动的溶质通量的竞争对手净SGD输入和河流输入。另一个新的发现是，水柱NO3-在表面河口有效地隔离由于SGD，可能是由于强烈的反硝化作用发生在缺氧的地下河口。(C)2016爱思唯尔有限公司版权所有。
Pore water exchange (PEX) and submarine groundwater discharge (SGD) represent two mechanisms for solute transport from the seabed into the coastal ocean. However, their relative importance remains to be assessed. In this study, we pursued the recently developed Ra-224/Th-228 disequilibrium approach to quantify PEX fluxes of Ra-224 into the Jiulong River estuary, China. By constructing a full mass balance of water column Ra-224, we were allowed to put various source terms, i. e., SGD, diffusive and advective pore water flow (PEX), and river input in a single context. This led to the first quantitative assessment of the relative importance of PEX vs. SGD in the delivery of solutes into an estuary. We carried out two surveys in the Jiulong River estuary: one in January 2014 (winter survey), the other in August 2014 (summer survey). By virtue of a 1-D mass balance model of Ra-224 in the sediment column, we demonstrated that PEX fluxes of Ra-224 were highly variable, both temporally and spatially, and can change by 1-2 orders of magnitude in our study area. Moreover, we identified a strong correlation between Ra-224-based irrigation rate and 234 Th-based sediment mixing rate. Our results highlighted irrigation as the predominant PEX process for solute transfer across the sediment-water interface. Total PEX flux of Ra-224 (in 10(10) dpm d(-1)) into the Jiulong River estuary was estimated to be 22.3 +/- 3.0 and 33.7 +/- 5.5 during the winter and summer surveys, respectively. In comparison, total SGD flux of Ra-224 (in 10(10) dpm d(-1)) was 11.3 +/- 8.6 and 49.5 +/- 16.3 in the respective seasons. By multiplying the PEX fluxes of Ra-224 by the ratio of the concentration gradients of component/Ra-224 at the sediment-water interface, we quantified the total PEX fluxes of dissolved inorganic carbon (DIC) and nutrients (NH4+, NO3-, and H4SiO4) into the Jiulong River estuary. In the meantime, net export of DIC and nutrients via SGD were estimated by multiplying the SGD fluxes of Ra-224 by the DIC (nutrients)/Ra-224 ratios in the SGD end-members around this area. Our results revealed that PEX-driven fluxes of solutes rival net SGD input and river input in an estuary. An additional new finding is that water column NO3- in the surface estuary was effectively sequestered due to SGD, probably as a result of intense denitrification occurring in the anoxic subterranean estuary. (C) 2016 Elsevier Ltd. All rights reserved.