Altitudinal gradients of pollutant input in the Austrian Alps

Long-term measurements in Austria and especially at altitudinal profiles in Tyrol showed, that the concentrations of air pollutants (sulfur dioxide, nitrogen oxides, ozone) vary with altitude above sea level and altitude above valley bottom, respectively. While sulfur dioxide and nitrogen dioxide concentrations decrease, those of ozone increase with altitude. The maximum values of the nitrogen input by wet deposition in Austria is in about 500m a.s.l. The contribution of occult deposition (fog) to the total input is high at higher elevations. Corresponding to the pollutant impact to forest trees, bioindication methods reflect the impact of the local pollutant cocktail at different elevations. The content of deposed pollutants (e.g. Pb) give a hint to the input quantities. Responses of antioxidative compounds in leaves/needles (e.g. ascorbate, thiols) allow the quantification of stress reactions of trees, either as a reaction to gaseous compounds, e.g. photochemical oxidants, or to natural stresses or to combinations.

Ozone / antioxidative system

Ozone concentrations in Central Europe: Mean ozone concentrations increase with altitude up to the timberline. At 500m a.s.l., the annual mean values range from 12 to 40 ppb, at 2000m a.s.l. from 40 to 55 ppb. Ozone limit values (e.g. the AOT40 of the UN-ECE) are exceeded to a high extent above 500m a.s.l.

Compounds of the antioxidative system: Higher antioxidant levels protect plants from oxidative stress which can be caused by pollutants (e.g. ozone), but also by natural stresses in high elevations. Antioxidants in needles (e.g. ascorbate, thiols) increase and chlorophylls decrease with altitude, indicating increased protection from oxidative stress. Thiols contain sulfur and hence are also related to sulfur impacts at lower elevations.

Nitrogen

Wet deposition of nitrogen in Central Europe: Nitrogen input by wet deposition rather decreases with altitude. Critical Loads are exceeded at most of the stations. The annual nitrogen input ranges from 5 to 40 kg N ha-1 a-1 at lower altitudes; maximum input decreases with altitude (e.g., from 5 to 20 kg N ha-1 a-1 at 1500m a.s.l.).

Wet, dry & occult deposition of nitrogen at an altitude profile in Achenkirch/Tyrol: The contribution of occult deposition (fog) to the total deposition is important at higher altitudes. Whereas the amount of occult deposition was low in 920m a.s.l. (lower than 1%), it was high in 1758m (approx. 23%).

Concentration of nitrogen in needles

At two altitudinal profiles in Tyrol (Zillertal 1984-1997; Achenkirch, 1984-2000) the mean nitrogen content of the needles decreased with altitude.

Within the Austrian Bioindicator Grid (611 plots), the N content (1983-2000) also decreased with altitude.

The main amount of the plots showed insufficient nutrition (lower than 1,5% N) and deficiency, respectively (lower than 1,3%).

Lead

Wet, dry & occult deposition of Pb at the altitudinal profile Achenkirch/Tyrol: The share of occult deposition of Pb at 1758m a.s.l. leads to a two-fold input compared to the valley station Mühleggerköpfl (Achenkirch/Tyrol). During the measuring period the Pb input amounted to 17.4 g ha-1 a-1 in 1758 m and to 9.9 g ha-1 a-1 in 920 m a.s.l. The input remained far below the limit value for Pb according to the "2. Verordnung gegen Forstschädliche Luftverunreinigungen" / BGBl. 199/1984 (2500 g ha-1 a-1). This was also true for Cd, Cu and Zn.

Concentration of Pb in bark (Tyrol): Pb accumulates in the bark and in the needles of Norway spruce. At the altitudinal profile Achenkirch, the mean concentrations (sampling 1982 and 1985) decreased markedly with altitude from 15 to 3 mg Pb/kg.

Concentration of Pb in spruce needles at the altitudinal profiles Zillertal (1984-1997) and Achenkirch (1984-2000), the mean concentrations did not show an altitudinal dependence of Pb concentrations in needles. The Pb concentrations ranged from 0.1 to 1 mg Pb/kg.