Freshwater lenses as archive of climate, groundwater recharge, and hydrochemical evolution: Insights from depth‐specific water isotope analysis and age determination on the island of Langeoog, Germany
Freshwater lenses as archive of climate, groundwater recharge, and hydrochemical evolution: Insights from depth‐specific water isotope analysis and age determination on the island of Langeoog, Germany
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DOI：
10.1002/2014wr015584
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发表时间：
2014-10
影响因子：
5.4
通讯作者：
G. Houben;P. Koeniger;J. Sültenfuss
中科院分区：
文献类型：
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作者：
G. Houben;P. Koeniger;J. Sültenfuss
在德国Langeoog岛，通过深度特定采样和使用氚-氦法的地下水定年，重建了淡水透镜体的年龄分层。分层受土地利用及其导致的补给速率差异的强烈影响。由于干沙的排斥作用，沙丘顶部的入渗明显低于山谷。沙丘谷对每个地区地下水补给的贡献是其他地区的四倍。因此，沙丘地区的住房开发可能会大大减少可用的新鲜地下水。淡水柱稳定同位素值随深度的减小而明显增加。因此，淡水透镜包含了一个气候档案，反映了在补给时不断变化的环境条件。结合氚-氦定年，这种模式可以与气候记录相匹配，这些记录显示在过去50年中，在补给时间和降雨率的温度增加。在通过透镜的过程中，水化学的时空发展遵循一个明显的模式，从低电导率的钠和氯化物为主的雨水到更矿化的碳酸氢钠水类型，这是由靠近表面的碳酸盐壳溶解和随后更深部分钙离子交换钠引起的。
The age stratification of a freshwater lens on the island of Langeoog, Germany, was reconstructed through depth‐specific sampling and groundwater dating using the tritium‐helium method. The stratification is strongly affected by the land use and resulting differences in recharge rates. Infiltration at the dune tops is significantly lower than in the valleys, due to repellency of the dry sand. Dune valleys contribute up to four times more groundwater recharge per area than other areas. Housing development in dune areas might therefore significantly decrease the available fresh groundwater. The freshwater column shows a distinct increase of stable isotope values with decreasing depths. Hence, the freshwater lens contains a climate archive which reflects changing environmental conditions at the time of recharge. Combined with tritium‐helium dating, this pattern could be matched to climate records which show an increase of the temperature at the time of recharge and rainfall rates during the last 50 years. The spatial and temporal developments of water chemistry during the passage through the lens follow a marked pattern from a sodium and chloride‐dominated rainwater of low conductivity to a more mineralized sodium bicarbonate water type, caused by dissolution of carbonate shells close to the surface and subsequent ion exchange of calcium for sodium in the deeper parts.