Lin Jiajia, Compton Jana E, Clark Chris, Bittman Shabtai, Schwede Donna, Homann Peter S, Kiffney Peter, Hooper David, Bahr Gary, Baron Jill S
The Oak Ridge Institute for Science and Education (ORISE). 200 SW 35th St., Corvallis, OR 97333.
U.S. Environmental Protection Agency, Pacific Ecological Systems Division, 200 SW 35th St., Corvallis OR 97333.
J Geophys Res Biogeosci. 2020 Sep 1;125(9). doi: 10.1029/2019jg005577.
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, US) using locally-derived data, national statistics and standard parameters. Feed imports for dairy (mainly in the US) 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 US 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.
流域氮（N）预算为地下水和地表水氮污染的驱动因素及解决方案提供了见解。我们利用本地获取的数据、国家统计数据和标准参数，为跨界的努克萨克河流域（加拿大不列颠哥伦比亚省和美国华盛顿州）构建了一个全面的氮预算。奶牛（主要在美国）和家禽（主要在加拿大）的饲料进口分别占该流域总氮输入的30%和29%。合成肥料是第二大氮源，占氮输入的21%。人类和宠物的食品进口合计占总输入的9%，低于大气沉降（10%）。洄游鲑鱼带回的海洋源氮占总氮输入的比例不到0.06%。量化的氮输出占总氮输入的80%，主要由氨排放驱动（占氮输出的32%）。动物产品出口是第二大氮输出（31%），包括美国的牛奶和牛以及加拿大的家禽产品。河流氮输出估计占总氮输出的28%。仅常用的作物氮利用效率（NUE）指标并不能提供足够的农业活动信息，但与其他标准（如农场门口的NUE）结合使用可能能更好地反映管理效率。由于农业在该地区的重要性，它是氮输入环境的主要驱动因素；氮预算信息可为管理工作提供参考，以尽量减少氮损失。氮预算为跨部门和跨境的利益相关者提供关键信息，以制定环境和经济上可行且有效的解决方案。
