Groundwater and surface water contamination by nitrogen can produce serious health issues particularly regarding the contraction of methemoglobinemia in infants; prevention of this disorder is a main reason for regulating drinking water quality in New Zealand. To assist the management of water quality in the Upper Waikato Catchment in the light of growing intensification of nitrogen producing land uses, a regional groundwater flow and contamination transport model was developed to assess probable future nitrogen concentrations. Calibration of the steady state model was achieved with a root mean square error of 4.7% for groundwater levels and 7.9% for gains and losses in river flow within the catchment. Model performance was assisted by relationships determined between SiO₂ concentrations in groundwater and water age. Modelling coupled with water aging indicates that the mean residence time of contributing water in the Upper Waikato Catchment ranges from 5 to 101 years with an average of 50 years. Some 77% of surface water is sourced from groundwater which is likely to convey the predominant contribution to the total nitrogen load. Nitrogen concentrations are increasing but the long-term total load is difficult to estimate owing largely to lack of information about historical land use and the degree of attenuation of nitrogen. The model and results obtained may be employed to provide information on water travel time distributions, appropriate source location and surface water receiving reaches in rivers and streams all of which is important and necessary for effective water quality management in the Catchment.

氮污染地下水和地表水会产生严重的健康问题，尤其是有关婴儿高铁血红蛋白收缩的问题；预防这种疾病是调节新西兰饮用水水质的主要原因。为了帮助怀卡托上游集水区的水质管理，因为氮生产用地的集约化发展，开发了区域地下水流量和污染物迁移模型，以评估未来可能的氮浓度。通过对流域内地下水位的均方根误差为4.7％，对河流流量得失的均方根误差为7.9％，实现了稳态模型的校准。SiO ₂之间确定的关系有助于模型性能地下水浓度和水龄。建模与水老化表明，上怀卡托集水区贡献水的平均停留时间为5至101年，平均为50年。约77％的地表水来自地下水，这很可能在总氮负荷中起主要作用。氮的浓度正在增加，但是长期的总负荷很难估算，这主要是由于缺乏有关历史土地使用和氮的衰减程度的信息。获得的模型和获得的结果可用于提供有关水流时间分布，河流和溪流中合适的水源位置和地表水接收河段的信息，所有这些对于在集水区进行有效水质管理都是重要和必要的。