A combined field and modeling study of groundwater flow in a tidal marsh
A combined field and modeling study of groundwater flow in a tidal marsh
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DOI：
10.5194/hess-16-741-2012
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发表时间：
2011-05
影响因子：
6.3
通讯作者：
Yuqiang Xia;Hailong Li
中科院分区：
文献类型：
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作者：
Yuqiang Xia;Hailong Li
在中国海南东寨港国家级自然保护区的红树林沼泽中发现了秃泥滩。为了探讨这种现象的可能原因，我们选择了地形和潮汐作用相似的红树林样带和秃滩样带的潮间带进行比较研究。在这两个样带，观测到的地下水位变化在高、低潮间带显著，在中潮间带可以忽略。尽管潮汐作用和上述相似之处相同，但红树林样带观测到的地下水盐度（平均23.0 ppt）明显小于秃滩样带（平均28.5 ppt）。这些观察结果提出了一个假设：潮汐沼泽的水力结构和淡水供应可能是对红树林发展至关重要的主要水文地质因素。二维数值模拟证实了这一推测，并给出了与观测到的地下水位一致的结果。研究发现，这两个样带具有泥砂双层结构：表面是低渗透泥浆带，下面是高渗透带，在高潮线和低潮线上露头。来自内陆的淡水补给沿红树林样带相当可观，但沿秃滩样带可以忽略不计。高渗透带可能为红树林沼泽植物提供了通过根部向下延伸到高渗透带吸收淡水和氧气的机会，这可能有助于限制根区因蒸散发引起的盐分积累，增强盐分的去除，从而可能进一步增加沼泽草的产量并影响其空间分布。秃顶的海滩很可能是由于缺乏足够的淡水来产生对红树林生长至关重要的微咸海滩土壤条件。海水通过高潮间带附近的露头渗入高渗带，并从低潮线附近的潮汐河岸排出。这些过程因此形成了潮汐诱导的海水-地下水循环，这可能对海底地下水排放总量（SGD）有相当大的贡献。最后，总结了本研究的意义和不确定性，以供将来的研究。
Bald mud beaches were found among the mangrove marshes in Dongzhaigang National Nature Reserve, Hainan, China. To investigate the possible reasons for this phenomenon, the intertidal zones of a mangrove transect and a bald beach transect with similar topography and tidal actions were selected for comparison study. Along both transects, observed water table variations were significant in the high and low intertidal zones and negligible in the middle intertidal zones. Despite the same tidal actions and above-mentioned similarities, observed groundwater salinity was significantly smaller along the mangrove transect (average 23.0 ppt) than along the bald beach transect (average 28.5 ppt). These observations invite one hypothesis: the hydraulic structure of tidal marsh and freshwater availability may be the main hydrogeological factors critical to mangrove development. Two-dimensional numerical simulations corroborated the speculation and gave results in line with the observed water table. The two transects investigated were found to have a mud-sand two-layered structure: a surface zone of low-permeability mud and an underlying high-permeability zone that outcrops at the high and low tide lines. The freshwater recharge from inland is considerable along the mangrove transect but negligible along the bald beach transect. The high-permeability zone may provide opportunity for the plants in the mangrove marsh to uptake freshwater and oxygen through their roots extending downward into the high-permeability zone, which may help limit the buildup of salt in the root zone caused by evapotranspiration and enhance salt removal, which may further increase the production of marsh grasses and influence their spatial distribution. The bald beach is most probably due to the lack of enough freshwater for generating a brackish beach soil condition essential to mangrove growth. It is also indicated that seawater infiltrated the high-permeability zone through its outcrop near the high intertidal zone, and discharged from the tidal river bank in the vicinity of the low tide line. These processes thereby formed a tide-induced seawater-groundwater circulation, which likely provided considerable contribution to the total submarine groundwater discharge (SGD). Finally, implications and uncertainties behind this study were summarized for future examinations.