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 (SO 4 ), nitrate (NO 3 ) 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:
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);
the key indicator soil nitrate leaching (NO3,leach):
frequency of sampling: every year;
the key indicator carbon-nitrogen ratio (C/N) and the supporting indicator of total nitrogen in soil (Ntot):
frequency of sampling: every 10 years;
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:
the key indicator vegetation growth and foliar damage and the supporting indicator carbon flux (Cflux):
frequency of sampling: every year;
the key indicator exceedance of flux-based critical levels:
frequency of sampling: every year during the growing season.