Groundwater nitrate is a concern in the Great Lakes Basin (GLB) of North America. Concentrations vary based on hydrogeologic setting and surface contamination pressures. The first objective of this study was to characterize groundwater nitrate trends in a spatial and temporal context across three unique hydrogeologic and land-use settings in the GLB, at research sites in Norfolk, Guelph, and Acton, in southwestern Ontario, Canada. The second objective was to compare groundwater nitrate trends at the sites to determine the potential influence of hydrogeologic setting on seasonal nitrate variability. Groundwater nitrate-N concentrations and additional parameters were measured at 25 monitoring wells at the three sites, once every 2 months from June 2014 to July 2016 (13 sampling events). The dominant land-use pressure at all three sites is agricultural; however, the type of agriculture and the amount of natural and urban land vary. The Guelph site had the highest nitrate concentrations, while the Acton and Norfolk mean concentrations were similar. Seasonally, nitrate was found to be highest during the spring and early summer periods at all three sites. Several monitoring locations had cyclical patterns in nitrate concentrations, while others remained consistent except for isolated peak events. Comparison of multiple years reveals the expression of a relationship between climatic conditions during winter months and nitrate concentrations, indicating the importance of antecedent conditions to groundwater nitrate concentrations. The combination of climatic conditions, land-use pressure, and hydrogeologic setting plays an important role in the characteristics of groundwater nitrate time-series trends.

地下水硝酸盐是北美大湖盆地（GLB）所关注的问题。浓度根据水文地质环境和表面污染压力而变化。这项研究的第一个目标是在加拿大安大略省西南部的诺福克，圭尔夫和阿克顿的研究地点，在GLB的三个独特的水文地质和土地利用环境中，描述时空背景下地下水硝酸盐趋势。第二个目标是比较站点的地下水硝酸盐趋势，以确定水文地质环境对季节性硝酸盐变化的潜在影响。从2014年6月至2016年7月，每2个月对这三个地点的25口监测井进行地下水硝酸盐氮浓度和其他参数的测量（13次采样事件）。这三个地点的主要土地利用压力是农业。但是，农业的类型以及自然和城市土地的数量各不相同。Guelph位点的硝酸盐浓度最高，而Acton和Norfolk的平均浓度相似。从季节性上看，春季和夏季初这三个地点的硝酸盐含量最高。几个监测点的硝酸盐浓度呈周期性变化，而其他监测点则保持一致，除了孤立的峰值事件。多年的比较揭示了冬季气候条件与硝酸盐浓度之间关系的表达，表明前期条件对地下水硝酸盐浓度的重要性。气候条件，土地利用压力，