Evidence for changing the critical level for ammonia

Area of Science:

• Ecology
• Environmental Science
• Plant Biology

Background:

• The current critical level for ammonia (CLE(NH3)) in Europe is 8 µg NH3 m⁻³ (annual average).
• Recent research indicates ammonia negatively impacts plant community composition at significantly lower concentrations.
• Existing methods for setting CLE(NH3) require review based on new evidence.

Purpose of the Study:

• To review current methods for establishing critical levels of ammonia (CLE(NH3)).
• To collate evidence on the ecological effects of ammonia on various plant types.
• To propose revised CLE(NH3) values for different European vegetation types.

Main Methods:

• Review of scientific literature and methods used to set CLE(NH3).
• Collating empirical evidence on ammonia's effects on plant communities.
• Proposing new CLE(NH3) values based on reviewed data.

Main Results:

• For lichens and bryophytes, a new long-term CLE(NH3) of 1 µg NH3 m⁻³ is proposed.
• For herbaceous species, a CLE(NH3) of 3±1 µg NH3 m⁻³ is proposed.
• Existing CLE(NH3) for forest trees is insufficient; 3±1 µg NH3 m⁻³ may exceed critical N deposition loads.

Conclusions:

• The current European CLE(NH3) is likely too high to prevent ecological damage.
• Revised CLE(NH3) values are proposed for lichens, bryophytes, and herbaceous plants.
• Further research is needed for forest trees, but proposed values suggest current N deposition limits may be exceeded.