Regionalized nitrogen fate in freshwater systems on a global scale

Abstract

Excessive nitrogen (N) use in agriculture, industry, and household waste leads to widespread N release throughout the environment, causing eutrophication in both freshwater and coastal areas. To better understand N-induced eutrophication and other N-use-related environmental impacts at the local scale, improvements in the spatial resolution of life cycle impact assessment measures are required. Here, we present a method to estimate gridded fate factors (FFs) at a half-degree resolution based on the Integrated Model to Assess the Global Environment-Global Nutrient Model to provide eutrophication indicators for global N-related manufacture, trade, and consumption in life cycle assessment. Across global freshwater systems, our cumulative FFs have a 5th percentile of 0.9 days and a 95th percentile of 184.0 days. Aggregated FFs for administrative units range from 0.3 days to 211.9 days. The hotspots of cumulative FFs are mainly distributed upstream of large reservoirs or lakes. On a global level, advection is the dominant process controlling the FF (69.7% of areas), followed by retention (29.0%), and water consumption (1.3%). N retention dominates in advection-favoring, high-discharge regions due to the high residence times, while water consumption tends to dominate water-scarce zones. The results demonstrate the importance of gridded information to assess eutrophication impacts, as it characterizes N emissions from anthropogenic sources at high spatial resolution in comparison to basin- or country-level assessments. Introducing soil–freshwater N fate complements existing P-related fates to improve global assessments of eutrophication. This article met the requirements for a Gold–Gold Badge JIE data openness badge described at http://jie.click/badges.