At a Seminar arranged by the Ecological Research Committee on October 30 , 1967, Dr. Svante Odén discussed the acidity and sulphur conditions over Europe and the consequensos to soils, surfaco waters and biological systems.
In 1952 a European network of stations for atmospheric chemistry was organized by the International Meteorological Institute , Stockholm (Fig. 1). Odén and Dr. Torsten Ahl, Uppsala, later complemented the network in Scandinavia with stations for surface water chemistry (Fig. 3).
At the atmospheric chemical network measurements of different element s havc been made for about 15 years. Changes of the atmospheric chemical climate can now be evaluated from the dat a, showing either positive or negative trends (Fig. 2 , 20 and 21). The sulphur content of air (Fig. 18) and of precipitation (Fig. 17 ) shows a characteristic pattern for Europe, indicating a close rolationship to air pollution from citiesand industrios. The rising sulphur content in the atmosphere are undoubtedly connected with the incrcasing use of sulphurous f'uels as a suostitute for coke and coal.
The increasing addition of sulphur compounds t o the atmosphere (mainly as SO2 and H2S ) leads to an incrcase of the acidity o f the precipitation. Monthly data from threc stations conccrning pH are given (Fig. 4 , 5 and 6) . With a few exceptions the pH valuos at the network stations are dccrcasing with time (Fig. 9, 10 and 11) . The ratc of decrcasc of the
1) Department of Pedology, Agricultural College of Sweden, Uppsala
2) Swedish Natural Science Research Council , Sveavägen 166, Stockholm 23
pH values shows a geographical distribution pattern (Fig. 12), which can be expected from the intensity of industrial activities.
The acidity of the yearly precipitation in Europe is mapped for 1958 (Fig. 13) , 1962 (Fig. 14) and 1965 (Fig. 15). In 1958 values below pH 5 were to be found only in a limited area over The Netherlands. As is shown on the succceding maps, this area has since spread over Central Europe. The other acid zones are also procecding and in 1965 the isoline for pH 4.5 had reached the Southern part of Sweden.
In 1967 the pH values for Central Sweden had decreased to approx. 4.3. A study of the wind trajectories (Fig. 8) shows, that this low pH value is partly a result of a transport of air pollutants from source to sink areas. "The Scandinavian Sulphur Depression" (Fig. 2 2) indicates that a complicated hydrometeorological mechanism is involved in the distributional pattern.
In 1965 almost a thousand Scandinavian lake and river waters were chemically investigatcd by Ahl and Odén. For considerable areas the pH-values were found to be so low as to affect fish life. The mapping of pH (Fig. 2 5 ) corresponds with that for Magnesium (Fig. 26) indicating a depletion of eations of the soil complex .. This is also reflected by thc long term changes of the concentration af anions ( so4) and cations (Ca) in river systems (Fig. 27 a and b).
Last summer a special study o f the acidity of 600 lakes in Western Scandinavia was made by Dr. E . Eriksson. The results showed that since 1959 the pH-values have boen reduced on an average by 0.4 units.
The acid precipitation will sooner or later acidify the river systers. The change in pH will depend, among others, on the buffer capacity of the catchment area. However, negative trends have already appeared in both large river systems (Fig. 23) and small ones (Fig. 24).
The acidification of natural waters can be a threat to aquatic life. Organisms cannot normally exist in water with pH-values below 4.0. Certain valuable fish, such as salmon, are threatened at pH 5.5 and the catch of salrnon in Mörrumsån is continuously decreasing (Fig. 28 ).
Soils may also be affected if the supply of nautralizing alkalis are depleted or poor. An impoverished forest arowth rate could be the result (Fig. 30). The important point is, according to Odén, that the balance of nature is considerably disturbed by the present atmospheric pollution of sulphuric acid and other acidifying compounds such as nitric and hydrochloric acid.
An atmospheric chemical atlas of Europe containing data on air as well as precipitation is being prepared on the basis of existing data.
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In the discussion that followed Odéns paper f'urther evidence of extensive fish kill in acid waters was given. Two speakers emphasized the economic aspects of the heavy damage that is caused each year by acid corrosion of metals, now amounting to 2 % of our gross national product, and the economic as well as cultural valuecs that are lost by the deterioration of buildnings and stone ornaments.
Ekologikommittén, Statens naturvetenskapliga forskningsråd , 1968. , 86 p.
Ekologi, miljö, förorening, syra, ph-värde, försurning, nederbörd, atomorsfärisk förorening