Analysis and modeling of watershed-scale nitrogen balance in relation to nitrogen pollution of unconfined groundwater in an alluvial fan

为了积累必要的数据，对泉水的流量和水质进行了实地测量。对不同污染源的出水氮负荷进行了研究。氮平衡分析结果表明，流域总氮负荷的一半以上来自奶牛养殖，牲畜排泄物中的大量氮储存在土壤中，并随雨水入渗进入地下水。幸运的是，尽管污染物流入量很大，但硝酸盐氮浓度没有达到环境基准值10mg/L，这是由于河流底流和稻田入渗的高地下水回灌率稀释造成的。在此基础上，对地下水水质过程进行了建模。该模型由地下水水文模型作为基本结构和污染物过程模型（行为方程）组成。建立了基于水箱模型的集总系统地下水模型和分布式系统地下水模型作为基本水文模型。第一种方法是将L-Q型和溶解型污染物行为方程与集总地下水模型相结合，建立集总系统地下水质量模型。该模型的应用表明，模型计算能较好地反映硝态氮浓度的季节变化。同时，由于集总模型无法表示流域内水质的分布特性，因此研究进入了下一步，即建立分布式系统地下水水质模型。采用网格型地下水渗流模型作为基础结构，并将两种类型的污染物行为方程相结合。利用输入的数据对流域内污染源的分布进行处理。该模型的结果可以反映氮负荷的空间运动趋势。少

Field measurements on discharge and water quality of spring water were carried out for accumulation of necessary data. Amounts and processes of effluent nitrogen load from the different pollution sources were also investigated. As the results of nitrogen balance analysis, it was clarified that more than half of the total nitrogen load of the basin came from dairy farming and massive nitrogen from live stock excreta was stored on/in the soil and intruded into the groundwater together with rainwater infiltration. The fortunate fact that despite the high pollutant inflow, the nitrate nitrogen concentration does not reach 10mg/L, the environmental benchmark value, was found to be explained by dilution by the high groundwater recharge rate from the river underflow and paddy field infiltration.Based on the above results, modeling of groundwater quality processes was conducted. The model consists of a groundwater hydrologic model as the basic structure and a pollutant process model (behavior … More equations). As the basic hydrologic model, a lumped system groundwater model based on Tank Model and a distributed system groundwater model were prepared. For the first approach, a lumped system groundwater quality model was developed by combining the L-Q type and dissolution type of pollutant behavior equations to the lumped groundwater model. Application of this model showed that the model calculation could represent the seasonal change in nitrate nitrogen concentration fairly well.Meanwhile, since the distributed property of water quality in the basin cannot be represented by the lumped model, the research proceeded to the next step for developing a distributed system groundwater quality model. A grid type groundwater flow model was employed as the base structure and the same two types of pollutant behavior equations were incorporated. Further, distribution of pollution sources in the basin was handled with the input data. The result of this model could represent the tendency of spatial movement of nitrogen load. Less