The Conductivity of Bark‐Extracts from Spruce, a Sensitive Indicator for Air Poilution. Bark of spruce is a useful and sensitive indicator for air pollution. The latter may be determined more precisely by electrolytic conductivity of bark extracts than by pH‐value or sulphate level of foliage. By an additional simple sulphate analysis of bark extracts the effects of SO2 may be distinguished from those of certain components in dust.

1. In 1953 the author published a simple test for the diagnosis of gas damage based on the observation that the more the leaves of conifers, specially of spruce (Picea abies), have been damaged by gaseous contaminants in the atmosphere, the more turbid are the watery decoctions they produce. The instructions for the so-called. "Trübungstest" (or "turbidity test", abbrev. TT) are now recapitulated in brief. For 20 years series of measurements have been conducted almost uninterruptedly on the basis of this test in areas affected by air pollution. These experiments have now made it possible to evaluate its agreement with other criteria and its applicability by using statistical methods. 2. There is considerable correlation between the TT and the sulphur content of leaves of spruce (r=0.68). 3. Proportionally to the SO-emissions the TT at first rises abruptly, but then continues to rise more slowly. Even small emissions that cause no visible changes in spruce, increase the TT significantly. In some gas-damaged areas the TT and the intensity of emissions correlate very closely (r=0.86). 4. A similar connexion exists between the maximal values of TT and the decline in annual growth. Whereas the TT correlates well with the width of the growth ring of one of the following years, it correlates less well with that of the same year; apparently growth lags behind the TT. 5. A diagnosis on the basis of the TT requires a large number of comparable data, given which, it not only proves to be an additional simple help for the classification of damaged zones, but, above all, it appears to be advantageous in marking off damaged areas and giving large-scale information as to the extent to which suspected areas are actually afflicted by gaseous pollutants.

No abstract

No abstract

No abstract