The 216 km2 Neuenhagen Millcreeck catchment can be characterized as a drought-sensitive landscape in NE Germany. It is therefore of fundamental human interest to understand how water that fell as precipitation moves through the unsaturated soils and recharges groundwater. Additionally, a better knowledge of nutrient transport from soil to groundwater is important, especially in landscapes with light sandy soils. For a better understanding of these processes a dual tracer field experiment with bromide (Br–) and deuterium (D2O) was carried out some years ago. The aim of the present study is to use the results of this experiment to model tracer transport in the unsaturated zone via two different concepts, the classical deterministic advection-dispersion equation and a new stochastic approach. The advantage of the stochastic modelling method proposed here for field-scale tracer application is to produce reliable information about expected total solute fluxes from the unsaturated zone to groundwater and about mean transit times. Moreover, this allows one to evaluate the mass of solute in the soil profile and to determine the range of water velocity fluctuations. Field experiments should be concentrated on estimation of fluctuation of water flow velocity to make stochastic models more accurate. To summarize, this work contributes to new modelling methods for the simulation of water and solute transport in unsaturated sandy soils which are heavily affected by droughts and irregular hydrological processes in the subsurface

216 平方公里的 Neuenhagen Millcreeck 集水区可以说是德国东北部的干旱敏感景观。因此，了解随着降水而下降的水如何穿过非饱和土壤并补给地下水，是人类的根本利益。此外，更好地了解从土壤到地下水的养分输送也很重要，尤其是在轻质沙质土壤的景观中。为了更好地了解这些过程，几年前进行了溴化物 (Br–) 和氘 (D2O) 双示踪剂现场实验。本研究的目的是利用该实验的结果通过两个不同的概念模拟非饱和区的示踪剂传输，即经典的确定性平流扩散方程和新的随机方法。这里提出的用于现场规模示踪剂应用的随机建模方法的优点是可以生成关于从非饱和区到地下水的预期总溶质通量和平均传输时间的可靠信息。此外，这允许人们评估土壤剖面中的溶质质量并确定水速波动的范围。现场试验应集中在水流速度波动的估计上，使随机模型更加准确。总而言之，这项工作有助于模拟受地下干旱和不规则水文过程严重影响的非饱和沙土中水和溶质运移的新建模方法