Nitrogen-induced terrestrial eutrophication: cascading effects and impacts on ecosystem services.

Area of Science:

• Environmental Science
• Ecology
• Ecosystem Services

Background:

• Human activities significantly increase nitrogen deposition in terrestrial ecosystems.
• This nitrogen deposition causes biodiversity loss, altered ecosystem functioning, and impacts human well-being.
• Linking nitrogen deposition levels to ecological effects and affected ecosystem services is challenging due to complex nitrogen cascade pathways.

Purpose of the Study:

• To synthesize information on nitrogen-induced terrestrial eutrophication.
• To link critical nitrogen load exceedances with human beneficiaries using established frameworks.
• To identify ecological impacts and affected ecosystem services across different ecoregions.

Main Methods:

• Expert workshop to synthesize published literature on nitrogen deposition effects.
• Application of the STressor-Ecological Production function-final ecosystem Services Framework.
• Utilized the Final Ecosystem Goods and Services Classification System (FEGS-CS) to categorize impacts.

Main Results:

• 21 nitrogen critical loads were exceeded across five North American ecoregions, with deposition ranging from 2 to 39 kg N·ha⁻¹·yr⁻¹.
• 582 pathways linked critical load exceedances to 198 regional human beneficiaries and 66 Final Ecosystem Goods and Services (FEGS).
• Grasses/forbs, mycorrhizal communities, tree species, and lichen biodiversity were key biological indicators affected; Eastern Temperate Forests showed the most impacts.

Conclusions:

• Terrestrial eutrophication from nitrogen deposition is widespread, affecting all examined ecosystems nationally.
• The study identifies specific human beneficiaries and ecosystem services impacted by nitrogen deposition.
• Results highlight key uncertainties and knowledge gaps for future research on nitrogen impacts.