Watershed nitrogen (N) budgets provide insights into drivers and solutions for groundwater and surface water N contamination. We constructed a comprehensive N budget for the transboundary Nooksack River Watershed (British Columbia, Canada, and Washington, USA) using locally derived data, national statistics, and standard parameters. Feed imports for dairy (mainly in the United States) and poultry (mainly in Canada) accounted for 30% and 29% of the total N input to the watershed, respectively. Synthetic fertilizer was the next largest source contributing 21% of inputs. Food imports for humans and pets together accounted for 9% of total inputs, lower than atmospheric deposition (10%). N imported by returning salmon representing marine‐derived nutrients accounted for <0.06% of total N input. Quantified N export was 80% of total N input, driven by ammonia emission (32% of exports). Animal product export was the second largest output of N (31%) as milk and cattle in the United States and poultry products in Canada. Riverine export of N was estimated at 28% of total N export. The commonly used crop nitrogen use efficiency (NUE) metric alone did not provide sufficient information on farming activities but in combination with other criteria such as farm‐gate NUE may better represent management efficiency. Agriculture was the primary driver of N inputs to the environment as a result of its regional importance; the N budget information can inform management to minimize N losses. The N budget provides key information for stakeholders across sectors and borders to create environmentally and economically viable and effective solutions.

中文翻译：

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美加跨界流域氮预算的关键组成部分和对比


流域氮 (N) 预算提供了有关地下水和地表水氮污染的驱动因素和解决方案的见解。我们利用当地获得的数据、国家统计数据和标准参数，为跨界努克萨克河流域（加拿大不列颠哥伦比亚省和美国华盛顿）制定了全面的氮预算。乳制品（主要在美国）和家禽（主要在加拿大）的饲料进口分别占流域氮输入总量的 30% 和 29%。合成肥料是第二大来源，占投入的 21%。人类和宠物的食品进口合计占总投入的 9%，低于大气沉降 (10%)。返回鲑鱼输入的氮（代表海洋来源的营养物质）占氮输入总量的<0.06%。在氨排放（占出口的 32%）的推动下，量化氮出口占氮输入总量的 80%。动物产品出口是第二大氮产量（31%），其中美国是牛奶和牛，加拿大是家禽产品。河流氮出口量估计占氮出口总量的 28%。常用的作物氮利用效率 (NUE) 指标本身并不能提供有关农业活动的足够信息，但与农场 NUE 等其他标准相结合可能更好地代表管理效率。由于其区域重要性，农业是环境氮输入的主要驱动力； N预算信息可以告知管理层以尽量减少N损失。 N 预算为跨部门和跨国界的利益相关者提供关键信息，以创建环境和经济上可行且有效的解决方案。