Annex V OPTIONAL INDICATORS FOR MONITORING AIR POLLUTION IMPACTS REFERRED TO IN ARTICLE 9

for freshwater ecosystems: establishing the extent of biological damage, including sensitive receptors (microphytes, macrophytes and diatoms), and loss of fish stock or invertebrates:

• the key indicator acid neutralising capacity (ANC) and the supporting indicators acidity (pH), dissolved sulphate (SO₄), nitrate (NO₃) and dissolved organic carbon:

• frequency of sampling: from yearly (in lake autumn turnover) to monthly (streams).

for terrestrial ecosystems: assessing the soil acidity, soil nutrients loss, nitrogen status and balance as well as biodiversity loss:

1. (i)

   the key indicator soil acidity: exchangeable fractions of base cations (base saturation) and exchangeable aluminium in soils:

   • frequency of sampling: every 10 years;

   • supporting indicators: pH, sulphate, nitrate, base cations, aluminium concentrations in soil solution:

   • frequency of sampling: every year (where relevant);

2. (ii)

   the key indicator soil nitrate leaching (NO_3,leach):

   frequency of sampling: every year;

3. (iii)

   the key indicator carbon-nitrogen ratio (C/N) and the supporting indicator of total nitrogen in soil (N_tot):

   frequency of sampling: every 10 years;

4. (iv)

   the key indicator nutrient balance in foliage (N/P,N/K, N/Mg):

   frequency of sampling: every four years.

for terrestrial ecosystems: assessing ozone damage to vegetation growth and biodiversity:

1. (i)

   the key indicator vegetation growth and foliar damage and the supporting indicator carbon flux (C_flux):

   frequency of sampling: every year;

2. (ii)

   the key indicator exceedance of flux-based critical levels:

   frequency of sampling: every year during the growing season.