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THE REGIONS

• Upland UK
• Germany
• Scandinavia
• Italy
• Czech Republic
• Slovakia
• Pan-European

RESULTS

• Upland UK
• Germany
• Scandinavia
• Italy
• Czech Republic
• Slovakia
• Pan-European

Southern Alps, Italy

In North Italy, high emission of sulphur and nitrogen oxides and of ammonia are reported for the Po Plain, which host large towns like Milan and Turin. Therefore, the Southern slope of Central Alps receive sulphur deposition of between 3 and 16 kg/ha/yr, while ammonium and nitrate deposition are in the range 1.4-12 and 1.6-10 kg/ha/yr, respectively (Mosello & Marchetto, 1995). Ion concentration regularly decrease northwards. Sulphate deposition declined by about 50% from 1984 to 1998, while nitrate increased from 1984 to 1992 followed by a decrease. The general nitrogen deposition is greater than sulphur deposition, this trend is expected to extend to other European areas as a consequence of decreasing sulphur emissions and deposition. Specific to Northern Italy and the southern Alps there are also the high concentrations of ammonium in the precipitation. Ammonium counteracts the acidity of atmospheric deposition, leading to lower values of pH, but it increases the potential acidity, i.e. when ammonium reaches the soil, uptake by vegetation releases a mole of H⁺ for each mole of ammonium, otherwise the ammonium is oxidised through bacterial processes, with a production of two moles of H⁺ for every mole of ammonium oxidised (De Vries et al., 1994). Episodic deposition of alkaline Saharan dust is a further important feature of atmospheric deposition in Southern Europe, including Italy and the Alps. (De Angelis & Guidichet 1991; Rodà et al., 1992). Geological features of this area are very heterogeneous, and most of the larger lakes and rivers are not sensitive to acidification as their watershed are composed of, to a smaller or larger extent, of calcareous rocks. On the contrary, a number of high mountain lakes are lying in watershed mainly or exclusively formed on acidic rocks, like granites and gneiss. Low weathering rates, shallow soils and steep slopes contribute to an increased sensitivity of high mountain lakes to atmospheric pollution. In the area selected for this study, which comprises the Ossola and Sesia Valleys, 18%, 39% and 67% of the Alpine lakes show ANC values of below 20, 50 and 200 µeq l^-1.

Map of the Region

Lake Maggiore watershed is located within the study region

Courtesy of Rosario Mosello, Maria Cristina Brizzio, Michela Rogora, Aldo Marchetto and Gabriele A. Tartari

(C.N.R. Istituto Italiano di Idrobiologia, Largo Tonolli 50, I-28922 Verbania Pallanza (VB))

The Lake Maggiore watershed (below left) extends for 6,599 km² shared between Italy (50.4%) and Switzerland (49.6%). It contains more than two hundred headwater lakes, located between 1,200 and 2,800 m a.s.l., and more than twenty low altitude lakes, including Lake Lugano, Varese and Mergozzo.

This area receives a high amount (1,100 - 2,700 mm y^-1) of orographic precipitation (above right) when moist air masses coming from the sea reaches the Alps. Before reaching the Lake Maggiore watershed, the air masses cross the highly industrialized Po plain.

Since 1981, atmospheric deposition has been sampled weekly in up to six sites using wet-only samplers (below left). Samples were analysed for pH, conductivity, alkalinity (Gran titration), ammonium (indophenol blue) and Ca⁺⁺, Mg⁺⁺, Na⁺, K⁺, Cl^-, NO₃^- and SO₄⁺ (ion cromatography).

Major ion concentrations in atmospheric deposition show a regular gradient from the plain to the Alps (above right). A peculiar characteristics of atmospheric deposition in this area is high ammonium concentration, comparable to that of nitrate. Moving away from the industrial area, the SO₄⁺ and N concentration in atmospheric deposition decreases significantly.

Three subalpine rivers with minimal human disturbance in the watershed were selected (below left). Since 1971 (C) or 1984 (A and B), they has been sampled monthly. Samples were analysed for pH, conductivity, alkalinity (Gran titration), ammonium (indophenol blue) and Ca⁺⁺, Mg⁺⁺, Na⁺, K⁺, Cl^-, NO₃^- and SO₄⁺ (ion cromatography), reactive P and Si (molibdate) and total N and P (digestion with borate buffer

Following Traaen & Stoddard (1995), seasonal patterns of nitrate show that: rivers A and B in the southern part of the study area (all values in the growing season > 50 &microeq l^-1) have reached saturation stage 3, while river C, in the middle part of the study area (with values higher and lower than 50 &microeq l^-1), is in saturation stage 2/3 (above right). In any case, the atmospheric load of nitrogen is far in excess of the uptake capability of catchment vegetation.

REGIONS

REFERENCES

Reference: Traaen T.S & J.L. Stoddard. 1995. Assessment of nitrogen leaching from watersheds concluded in ICP on waters. NIVA Report, Oslo: 39 pp.