Cold agricultural regions are getting warmer and experiencing shifts in precipitation patterns, which affect hydrological transport of nutrients through reduced snowpack and higher annual proportions of summer rainfall. Previous work has demonstrated that the timing of phosphorus (P) concentrations is regionally coherent in streams of the northern Great Plains, suggesting a common climatic driver. There has been less investigation into patterns of stream nitrogen (N), despite its importance for water quality. Using high-frequency water quality data collected over 6 yr from three southern Manitoba agricultural streams, the goal of this research was to investigate seasonal patterns in N and P concentrations and the resultant impacts of these patterns on N/P stoichiometry. In the spring, high concentrations of inorganic N were associated with snowmelt runoff, while summer N was dominated by organic forms; inorganic N concentrations remained consistently low in the summer, suggesting increased biological N transformation and N removal. Relationships between N concentration and discharge showed generally weak model fits (r² values for significant relationships ranging from .33 to .48), and the strength and direction of model fits differed among streams, seasons, and forms of N. Dissolved organic N concentrations were strongly associated with dissolved organic carbon. Nitrogen-to-phosphorus ratios varied among streams but were significantly lower during summer storm events (p < .0001). These results suggest that climate-driven shifts in temperature and precipitation may negatively affect downstream water quality in this region.

中文翻译：

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寒冷地区农业河流中的氮动力学和氮磷化学计量学

寒冷的农业地区正变得越来越暖和，并且正在经历降水模式的变化，这通过减少积雪和更高的夏季降雨量来影响养分的水文输送。先前的工作表明，大平原北部河流中磷（P）浓度的时间分布在区域上是连贯的，这表明是常见的气候驱动因素。尽管氮对水质很重要，但对流氮 (N) 模式的研究较少。使用从曼尼托巴省南部三个农业河流收集的 6 年多来的高频水质数据，本研究的目标是调查 N 和 P 浓度的季节性模式以及这些模式对 N/P 化学计量的影响。在春天，高浓度的无机氮与融雪径流有关，而夏季的氮以有机物形式为主。夏季无机氮浓度始终较低，表明生物氮转化和氮去除增加。N 浓度与排放量之间的关系显示出普遍较弱的模型拟合（r ²的显着关系值介于0.33至0.48之间，并且模型拟合的强度和方向在氮的流量，季节和形式之间也不同。溶解的有机氮浓度与溶解的有机碳密切相关。氮磷比在溪流之间变化，但在夏季暴风雨期间明显降低（p  <.0001）。这些结果表明，气候驱动的温度和降水变化可能对该地区的下游水质产生负面影响。