van Grinsven Hans J M, Bouwman Lex, Cassman Kenneth G, van Es Harold M, McCrackin Michelle L, Beusen Arthur H W
J Environ Qual. 2015 Mar;44(2):356-67. doi: 10.2134/jeq2014.03.0102.
Historical trends and levels of nitrogen (N) budgets and emissions to air and water in the European Union and the United States are markedly different. Agro-environmental policy approaches also differ, with emphasis on voluntary or incentive-based schemes in the United States versus a more regulatory approach in the European Union. This paper explores the implications of these differences for attaining long-term policy targets for air and water quality. Nutrient surplus problems were more severe in the European Union than in the United States during the 1970s and 1980s. The EU Nitrates and National Emission Ceilings directives contributed to decreases in fertilizer use, N surplus, and ammonia (NH) emissions, whereas in the United States they stabilized, although NH emissions are still increasing. These differences were analyzed using statistical data for 1900-2005 and the global IMAGE model. IMAGE could reproduce NH emissions and soil N surpluses at different scales (European Union and United States, country and state) and N loads in the Rhine and Mississippi. The regulation-driven changes during the past 25 yr in the European Union have reduced public concerns and have brought agricultural N loads to the aquatic environment closer to US levels. Despite differences in agro-environmental policies and agricultural structure (more N-fixing soybean and more spatially separated feed and livestock production in the United States than in the European Union), current N use efficiency in US and EU crop production is similar. IMAGE projections for the IAASTD-baseline scenario indicate that N loading to the environment in 2050 will be similar to current levels. In the United States, environmental N loads will remain substantially smaller than in the European Union, whereas agricultural production in 2050 in the United States will increase by 30% relative to 2005, as compared with an increase of 8% in the European Union. However, in the United States, even rigorous mitigation with maximum recycling of manure N and a 25% reduction in fertilizer use will not achieve the policy target to halve the N export to the Gulf of Mexico.
欧盟和美国氮（N）预算以及向空气和水排放的历史趋势和水平明显不同。农业环境政策方法也存在差异，美国侧重于自愿性或基于激励的计划，而欧盟则采取更具监管性的方法。本文探讨了这些差异对实现空气和水质长期政策目标的影响。在20世纪70年代和80年代，欧盟的养分过剩问题比美国更为严重。欧盟的《硝酸盐指令》和《国家排放上限指令》促使化肥使用量、氮过剩量和氨（NH₃）排放量下降，而在美国，这些指标趋于稳定，尽管NH₃排放量仍在增加。利用1900 - 2005年的统计数据和全球IMAGE模型对这些差异进行了分析。IMAGE模型能够在不同尺度（欧盟和美国、国家和州）上再现NH₃排放量和土壤氮过剩量，以及莱茵河和密西西比河的氮负荷。过去25年中欧盟由监管驱动的变化减少了公众的担忧，并使进入水生环境的农业氮负荷更接近美国的水平。尽管农业环境政策和农业结构存在差异（美国种植更多固氮大豆，饲料和牲畜生产在空间上的分离程度高于欧盟），但目前美国和欧盟作物生产中的氮利用效率相似。IMAGE模型对国际农业知识与技术促进发展评估（IAASTD）基线情景的预测表明，到2050年向环境中的氮负荷将与当前水平相似。在美国，环境氮负荷仍将大幅低于欧盟，而到2050年美国的农业产量相对于2005年将增长30%，相比之下欧盟增长8%。然而，在美国，即使采取严格的减排措施，最大限度地回收粪肥氮并将化肥使用量减少25%，也无法实现将向墨西哥湾的氮出口量减半的政策目标。
