Characterization of nitrogen emissions for freshwater eutrophication modelling in life cycle impact assessment at the damage level and urban scale

Human interventions mobilize massive nitrogen (N) emissions to freshwater and result in serious eutrophication impacts. Life cycle impact assessment (LCIA) provides a reliable quantitative tool to address the challenges of potential ecological impact induced by increasing nutrient inputs. However, characterization procedures that relate N emissions to ecological damage in freshwater ecosystems in LCIA methodology are still lacking. This study aims to propose a spatially explicit characterization model (1 km × 1 km) for N-induced freshwater eutrophication. A complete cause-effect chains linking the N emission with species loss endpoint impact was constructed, in which the site-specific fate factor modelling contained transfer and removal processes in terrestrial and freshwater compartments, and the mechanistic modelling of ecosystem exposure and damage effect were quantified with species loss. The eutrophication characterization was conducted with a case study in Guangzhou, China, and 1 km × 1 km spatial differentiation of eutrophication susceptibility was intuitively demonstrated, with higher values in the Pearl River Estuary area. Method comparisons and further improvements were discussed in support of model generalization and further application.