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Freshwater eutrophication: spatially explicit fate factors for nitrogen and phosphorus emissions at the global scale

Payen S., Cosme B., Elliott A.H.. 2021. International Journal of Life Cycle Assessment, 26 (2) : p. 388-401.

DOI: 10.1007/s11367-020-01847-0

Purpose: Spatially explicit freshwater eutrophication indicators in life cycle assessment focus on phosphorus as the sole contributor to such impacts. Nitrogen may also be an ecological limiting factor in freshwater systems, but commonly not modelled. This work aims at filling this gap by consistently developing fate factors (FFs) for both dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP), using the same underlying model of nutrient export by rivers. Methods: The present FFs were developed for application to both diffuse emissions from soil and point emissions of nutrients to freshwater. The fate processes modelled include nutrient attenuation from land to stream, in the river network, in artificial reservoirs and lakes and associated with water consumption. FFs were calculated at a river basin resolution with a global coverage and at the country and global scales by means of emission-weighting aggregation and distinguishing agricultural from non-agricultural emissions. Results and discussion: River basin-scale FFs range from 7.7 × 10-8 to 330 days for N emissions and from 3.0 × 10-8 to 520 days for P emissions. Fate factors are aggregated at country and global scale with applicability at such scales in mind. Global average FFs (in days) are FFsoil N global = 125; FFfw N global = 257; FFsoil P global = 23; FFfw P global = 247. Comparison of FFs calculated at various scales showed the importance of using FFs at the highest spatial resolution (i.e. river basin). However, the river basin resolution may be too coarse for certain large basins as demonstrated for the Waikato basin in New Zealand, where FFs calculated at the sub-basin scale varied significantly. The characterisation factors represent the potential contribution of N and P to freshwater eutrophication (in Neq and Peq). The N and P components can be aggregated into a single indicator expressed in “algae-equivalent” for co-limited catchments or when the limitation status is unknown. T

Mots-clés : cycle de l'azote; évaluation de l'impact; eau douce; phosphore; eutrophisation; impact sur l'environnement

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