A comprehensive planetary boundary-based method for the nitrogen cycle in life cycle assessment: Development and...

Area of Science:

• Environmental Science
• Life Cycle Assessment
• Ecology

Background:

• Current methods for assessing nitrogen cycle impacts in life cycle assessment (LCA) lack spatial resolution and environmental relevance.
• There is a need for methods that can quantify the impact of nitrogen emissions on the safe operating space (SOS) for natural ecosystems.

Purpose of the Study:

• To develop a spatially resolved method for quantifying the impact of nitrogen emissions on the safe operating space (SOS) for natural soil, freshwater, and coastal water.
• To identify potential planetary boundary hotspots in product life cycles and inform targeted interventions.
• To demonstrate the method's applicability using a case study on open-field tomato production.

Main Methods:

• Coupling existing environmental models with threshold and reference values for natural soil, freshwater, and coastal water.
• Developing spatially resolved characterization factors for nitrogen emissions.
• Applying two sharing principles ('status quo' and 'gross value added') to assign SOS.

Main Results:

• The developed method provides spatially resolved estimations of SOS for nitrogen emissions across different environmental compartments.
• A case study on tomato production revealed that impacts on SOS varied by farming area, receiving compartment, and sharing principle.
• A high nitrogen use efficiency scenario showed potential to mitigate SOS transgressions in some locations.

Conclusions:

• The developed spatially resolved method enhances the assessment of nitrogen cycle impacts within LCA, moving beyond generic approaches.
• The method can identify specific 'planetary boundary hotspots' and guide stakeholders in implementing effective interventions.
• Application alongside methods for other planetary boundaries is recommended to avoid sub-optimization and ensure comprehensive environmental management.