Impact of Gaseous Pollutants on the Forest Ecosystem

Abstract

Of particular interest are the findings that high concentrations of sulphur dioxide, nitrogen monoxide, nitrogen dioxide and ozone cause marked alterations in the concentration of carbon dioxide (Michaelis et al. 1988, 1989a,b, 1990, 1991, 1992; Michaelis and Theopold 1993). The temporal behaviour and the dimensions of this effect depend on the pollutant considered and its concentration. Such episodes occur at any time of the day and also during the vegetation rest. A general feature is an increase in the concentration of CO₂. The effect is superimposed upon the normal diurnal and seasonal variation. The amplitude often markedly exceeds the usual rise during the night, and the day-night rhythm can be changed over several days. As will be shown in Section 13.2, the events are characterized by fluxes of opposite sign, i.e. the deposition of pollutants causes a release of CO₂ from the ecosystem. These findings may be interpreted as the outcome of stress conditions. Such phenomena have to date not been reported in the literature on forest decline field studies.