Transport and transformation processes of nitrogen in the soil are an essential part of understanding the relationship between agricultural input and nitrate (NO₃⁻) concentrations in groundwater. The presented study describes these transformation processes around NO₃⁻ degradation at a water catchment in the Lower Rhine Embayment, Germany. Despite intensive agriculture, extracted groundwater at a depth of 21 to 22 m shows unexpectedly very low NO₃⁻ levels, below 3 mg/L NO₃⁻ for all wells. The local water supplier therefore carried out investigations in this area and generated soil data from 22 representative areas (142 soil samples from 82 drilling meters from the surface to a max. depth of 5.5 m) and groundwater analyses from 17 groundwater monitoring wells (from 3 to 5 m below ground surface). Soil types are predominantly luvisol and gleysol. The substrate in the topsoil is mainly clayey silt; underneath there are mostly medium-grained sands with partial silt intercalations which appear as a separate layer. Based on this dataset, the percolating water residence times and the NO₃⁻ leaching potential were calculated in this study. Together with the nitrogen surplus and with the help of reactive transport modelling, the denitrification potential in the vadose zone was simulated. The comparison of simulation results with laboratory-measured data shows a high correlation. Substantial NO₃⁻ reduction in the vadose zone was observed: dependent on soil type, reduction capacity and water residence time, up to 25% of the NO₃⁻ was reduced here. The applied modelling is considered an improvement in NO₃⁻ degradation potential assessment because it considers many relevant variables such as precipitation, soil parameters (grain size, field capacity, available water capacity, coarse fragments) and nitrogen input. Therefore, a transfer to other sites with comparable hydro(geo)logical conditions is possible, also due to relatively easily determinable input data. This assessment of nitrogen degradation in the vadose zone will be a useful tool for NO₃⁻ levels forecast in groundwater

土壤中氮的运输和转化过程是理解农业投入与地下水中硝酸盐 (NO ₃ ^- ) 浓度之间关系的重要组成部分。本研究描述了德国莱茵河下游集水区围绕 NO ₃ ^-降解的这些转化过程。尽管进行了集约化农业，但在 21 至 22 m 深处提取的地下水显示出出乎意料地非常低的 NO ₃ ^-水平，低于 3 mg/L NO ₃ ^-对于所有井。因此，当地供水供应商在该地区进行了调查，并从 22 个代表性区域（从地表 82 个钻井米到最大深度 5.5 m 的 142 个土壤样本）生成了土壤数据，并从 17 个地下水监测井（从 3至地表以下 5 m）。土壤类型主要是luvisol和gleysol。表土中的基质以粘土质粉砂为主；下面大部分是中粒砂，夹杂部分粉砂，作为单独的层出现。基于此数据集，渗滤水停留时间和 NO ₃ ^-本研究计算了浸出势。结合氮过剩和反应性输运模型，模拟了包气带中的反硝化潜力。模拟结果与实验室测量数据的比较显示出高度相关性。观察到包气带中NO ₃ ^-显着减少：取决于土壤类型、还原能力和水停留时间，这里最多减少25%的NO ₃ ^-。应用建模被认为是对 NO ₃的改进^-退化潜力评估，因为它考虑了许多相关变量，例如降水、土壤参数（颗粒大小、田间持水量、可用水容量、粗颗粒）和氮输入。因此，也由于相对容易确定的输入数据，可以转移到具有可比水文（地质）条件的其他地点。对包气带中氮降解的评估将成为预测地下水中NO ₃ ⁻水平的有用工具