Knowledge of the sources of surface water in riparian zones and floodplains is critical to understanding its role in runoff generation and impact on biogeochemical and ecological processes. In this study, we demonstrate the potential of integrated surface-subsurface hydrologic modeling (HydroGeoSphere) in combination with a hydraulic mixing-cell approach to decipher different sources of surface water and their mixing in space and time. We present a novel approach to processing the model data that allowed us to compare which mechanisms ultimately transferred water to the surface (delivery processes) and from where the surface water originated (geographical sources) for varying wetness states and phases of wetting or drying across 36 test locations within the riparian-stream continuum of an intensively-studied, humid-temperate, forested headwater catchment (45 ha). Consistent with current process understanding for the study site, water exfiltrating from the subsurface was simulated as the dominant source for riparian surface water and intermittent streamflow. The model further helped to specify the relevance of different subsurface stores, revealing a wetness-dependent activation of upslope source areas. Contributions of riparian overland flow and precipitation were minor during all investigated phases of wetting and drying. Moreover, the spatial variability of surface water sources proved to be smaller than expected for the heterogeneous patterns and frequencies of the surface saturation observed and simulated. Based on these findings, we discuss the value of hydraulic mixing-cell modeling to complement the planning and interpretation of field investigations and to enhance process understanding regarding the spatio-temporal sources of surface water.

中文翻译：

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时空地表水的来源：利用水力混合单元建模识别输送过程和地理来源

了解河岸带和洪泛区地表水的来源对于了解其在径流生成中的作用以及对生物地球化学和生态过程的影响至关重要。在这项研究中，我们展示了综合地表-地下水文建模 (HydroGeoSphere) 与水力混合单元方法相结合的潜力，以破译不同的地表水源及其在空间和时间上的混合。我们提出了一种处理模型数据的新方法，使我们能够比较哪些机制最终将水转移到地表（输送过程）以及地表水的来源（地理来源），以适应 36在经过深入研究的潮湿温带的河岸河流连续体中的测试地点，森林源头集水区（45 公顷）。与目前对研究地点的过程理解一致，从地下渗出的水被模拟为河岸地表水和间歇性水流的主要来源。该模型进一步帮助指定了不同地下存储的相关性，揭示了上坡源区域的湿度依赖性激活。在所有研究的润湿和干燥阶段，河岸地表水流和降水的贡献很小。此外，地表水源的空间变异性证明比观察和模拟的地表饱和度的不均匀模式和频率的预期要小。基于这些发现，