CIRAIG, Polytechnique Montréal, 3333 Chemin Queen-Mary, Montréal, QC, Canada.
Unilever Safety and Environmental Assurance Centre, Unilever R&D, Colworth Science Park, Sharnbrook MK44 1LQ, UK.
Sci Total Environ. 2020 May 1;715:136813. doi: 10.1016/j.scitotenv.2020.136813. Epub 2020 Jan 21.
Existing methods that apply the planetary boundary for the nitrogen cycle in life cycle assessment are spatially generic and use an indicator with limited environmental relevance. Here, we develop a spatially resolved method that can quantify the impact of nitrogen emissions to air, soil, freshwater or coastal water on "safe operating space" (SOS) for natural soil, freshwater and coastal water. The method can be used to identify potential "planetary boundary hotspots" in the life cycle of products and to inform appropriate interventions. The method is based on a coupling of existing environmental models and the identification of threshold and reference values in natural soil, freshwater and coastal water. The method is demonstrated for a case study on nitrogen emissions from open-field tomato production in 27 farming areas based on data for 199 farms in the year 2014. Nitrogen emissions were modelled from farm-level data on fertilizer application, fuel consumption and climate- and soil conditions. Two sharing principles, "status quo" and "gross value added", were tested for the assignment of SOS to 1 t of tomatoes. The coupling of models and identification of threshold and reference values resulted in spatially resolved characterization factors applicable to any nitrogen emission and estimations of SOS for each environmental compartment. In the case study, tomato production was found to range from not transgressing to transgressing its assigned SOS in each of the 27 farming areas, depending on the receiving compartment and sharing principle. A high nitrogen use efficiency scenario had the potential to reverse transgressions of assigned SOS for up to three farming locations. Despite of several sources of uncertainty, the developed method may be used in decision-support by stakeholders, ranging from individual producers to global governance institutions. To avoid sub-optimization, it should be applied with methods covering the other planetary boundaries.
现有的应用于生命周期评估中氮循环行星边界的方法在空间上是通用的，并且使用的指标与环境相关性有限。在这里，我们开发了一种空间分辨方法，可以量化氮排放对自然土壤、淡水和沿海水的“安全运行空间”（SOS）的空气、土壤、淡水或沿海水的影响。该方法可用于识别产品生命周期中潜在的“行星边界热点”，并为适当的干预措施提供信息。该方法基于对现有环境模型的耦合，以及在自然土壤、淡水和沿海水中确定阈值和参考值。该方法针对基于 2014 年 199 个农场数据的 27 个露天番茄生产区的氮排放案例研究进行了验证。氮排放是根据农场一级的数据模型化的，包括肥料施用、燃料消耗以及气候和土壤条件。为将 SOS 分配给 1 吨番茄，测试了“现状”和“总增加值”这两个共享原则。模型的耦合和阈值与参考值的确定导致了适用于任何氮排放的空间分辨特征因子，以及每个环境组别的 SOS 估算。在案例研究中，根据接收环境和共享原则，27 个生产区中的每一个都发现番茄生产从没有超出到超出其分配的 SOS。高氮利用效率情景有可能使多达三个生产地点的 SOS 超过情况得到逆转。尽管存在一些不确定性来源，但该方法可以由利益相关者（从单个生产者到全球治理机构）在决策支持中使用。为避免次优决策，应将其与涵盖其他行星边界的方法一起应用。
