Effects of Nitrogen Emissions on Fish Species Richness across the World’s Freshwater Ecoregions

Abstract

The increasing application of synthetic fertilizer has tripled nitrogen (N) inputs over the 20th century. N enrichment decreases water quality and threatens aquatic species such as fish through eutrophication and toxicity. However, the impacts of N on freshwater ecosystems are typically neglected in life cycle assessment (LCA). Due to the variety of environmental conditions and species compositions, the response of species to N emissions differs among ecoregions, requiring a regionalized effect assessment. Our study tackled this issue by establishing regionalized species sensitivity distributions (SSDs) of freshwater fish against N concentrations for 367 ecoregions and 48 combinations of realms and major habitat types globally. Subsequently, effect factors (EFs) were derived for LCA to assess the effects of N on fish species richness at a 0.5 degree × 0.5 degree resolution. Results show good SSD fits for all of the ecoregions that contain sufficient data and similar patterns for average and marginal EFs. The SSDs highlight strong effects on species richness due to high N concentrations in the tropical zone and the vulnerability of cold regions. Our study revealed the regional differences in sensitivities of freshwater ecosystems against N content in great spatial detail and can be used to assess more precisely and comprehensively nutrient-induced impacts in LCA.

Global Regionalized Characterization Factors for Phosphorus and Nitrogen Impacts on Freshwater Fish Biodiversity

“…These phenomena highlight the importance of considering the comprehensive effects of nutrients on biodiversity loss along with hypoxia when assessing the impacts of nutrient emissions. Several studies include the overall effects by linking the nutrient concentration and the species richness (Azevedo et al, 2013;Zhou et al, 2023). Based on the species richness-nutrient relationships, several LCA studies (e.g., LC-IMPACT (Azevedo et al, 2020), ReCiPe2016 (Huijbregts et al, 2017), and Jwaideh et al (2022) have conceptualized and calculated CFs from fate to effect without considering exposure.…”

“…Damage to biodiversity is often expressed through the potentially disappeared fraction (PDF) of species. In contrast to previous studies (Rosenbaum and Hauschild, 2015) that assessed impacts through the potentially affected fraction, we directly linked the nutrient concentration levels (kg/m 3 ) to PDF by regressing species sensitivity distributions (SSDs) for P following the method of Zhou et al (2023) to calculate EFs for P (PDF⋅m 3 /kg P) and N (PDF⋅m 3 /kg N).…”

“…However, the representativeness of the spatial variability of P impacts on freshwater species is insufficient since these studies only distinguish the relationships between species and P for four geographical zones globally. Other studies include fate factors (FFs) (Zhou et al, 2022) and effect factors (EFs) (Zhou et al, 2023) for N at half-degree resolution. However, none of these studies cover more than one nutrient concerning freshwater eutrophication.…”

“…Our study aims to develop regionalized CFs for both P and N over the world (with a 0.5 × 0.5-degree spatial resolution and yearly time step) while following the GLAM recommendations. Following the methods of Zhou et al (2022Zhou et al ( , 2023, we coupled the local nutrient fate and concentrations from the Integrated Model to Assess the Global Environment -Global Nutrient Model (IMAGE-GNM) (Beusen et al, 2015) to 41 years of freshwater fish species data (13,920 freshwater fish species) to estimate the impact at the local ecosystem level. Next, we employed GEPs (Verones et al, 2022) to extrapolate the regional species loss to global species loss.…”

Divergence Between Long‐Term and Event‐Scale Nitrate Export Patterns

“…High concentrations of reactive nitrogen (N) in freshwater, mainly as nitrate, remain a pervasive problem for drinking water and aquatic ecosystems (de Vries et al., 2011; Picetti et al., 2022; Zhou et al., 2023). Contemporary and legacy sources of reactive N, primarily from anthropogenic fertilizer application, are exceeding the safe operating space for the planetary N cycle (Richardson et al., 2023), necessitating careful management to avoid compromising food security (Basu et al., 2022).…”