The creation of artificial dunes for coastal protection may have important consequences for freshwater lenses in coastal aquifers. The objective of this study was to compare the recharge processes below such a young dune with scant vegetation to an older dune covered by grass and herbaceous vegetation. To this aim, soil and water samples were collected from the unsaturated zone at two sites on Langeoog Island in northern Germany, and the soil water was analysed for stable water isotopes and chloride. Recharge rates were calculated by using a new version of HYDRUS-1D, which was modified to simulate isotope fractionation during evaporation. Both the model outcomes and the data highlight the importance of fractionation, which is slightly more pronounced at the older, more vegetated dune. At the newly constructed dune, vegetation dieback seemingly reduces the importance of transpiration during summer. Recharge occurs year-round, albeit predominantly during the winter months. Calculated recharge rates are consistent with lysimeter measurements, but are significantly higher than previously reported rates based on groundwater age data, which is primarily attributed to the absence of dune shrub at the sites investigated here. More data are needed to establish the importance of soil-water repellency and overland flow. Based on the results, it is proposed that repeated isotope sampling can yield important insights into the dynamics of recharge processes, including their response to climate change.

为保护海岸而建造人工沙丘可能对海岸含水层中的淡水透镜体产生重要影响。这项研究的目的是比较这样一个植被稀少的年轻沙丘下的补给过程与覆盖着草和草本植被的较老沙丘的补给过程。为此，我们从德国北部 Langeoog 岛的两个地点的非饱和区采集了土壤和水样，并分析了土壤水中的稳定水同位素和氯化物。通过使用新版本的 HYDRUS-1D 计算补给率，该版本经过修改以模拟蒸发过程中的同位素分馏。模型结果和数据都强调了分馏的重要性，这在较老、植被较多的沙丘上更为明显。在新建的沙丘上，植被枯死似乎降低了夏季蒸腾的重要性。充电全年进行，尽管主要在冬季。计算的补给率与蒸渗仪测量值一致，但明显高于先前基于地下水年龄数据报告的补给率，这主要归因于此处调查的地点没有沙丘灌木。需要更多的数据来确定土壤拒水性和地表径流的重要性。基于这些结果，建议重复同位素采样可以对补给过程的动态产生重要的见解，包括它们对气候变化的响应。计算的补给率与蒸渗仪测量值一致，但明显高于先前基于地下水年龄数据报告的补给率，这主要归因于此处调查的地点没有沙丘灌木。需要更多的数据来确定土壤拒水性和地表径流的重要性。基于这些结果，建议重复同位素采样可以对补给过程的动态产生重要的见解，包括它们对气候变化的响应。计算的补给率与蒸渗仪测量值一致，但明显高于先前基于地下水年龄数据报告的补给率，这主要归因于此处调查的地点没有沙丘灌木。需要更多的数据来确定土壤拒水性和地表径流的重要性。基于这些结果，建议重复同位素采样可以对补给过程的动态产生重要的见解，包括它们对气候变化的响应。