Abstract
In the years 1970, 1980, 1985, 1995, 2005 and 2010, lichen mapping in the towns of Wetzlar and Giessen in Hesse was performed. The aim was to show the effects of immission load. Despite the application of modified test methods during the study period, the results can still be compared directly because they could be adapted to the requirements of the guidelines of the Association of German Engineers. Even the earlier study results could be interpreted partly within the scope of the guidelines. Parallel to the lichen mapping, comparative examinations of pH on tree bark were carried out. In both towns, the pH of the tree bark has been increasing continuously, presently almost reaching pre-industrial values. The increase was stronger in Wetzlar than in Giessen. In 1970, the lichen vegetation showed a complete depletion. Since then the number of species has risen significantly. This development happened faster and more intensely in Wetzlar. The comparison of the lichen vegetation between 1970 and 2010 also shows an increased existence of species that are favored by hypertrophic air contaminants. In the 2010 survey, some species considered as being promoted by global warming were found for the first time. The increase of the bark pH can be explained by the decreasing acid pollution, primarily SO2. This is also assumed to be the main cause for the increasing number of lichen species. An explanation for Wetzlar's advantage is that the acid pollutants had been neutralized by a local industrial emittent of lime dust. With the reduction of dust emissions in Wetzlar due to the installation of filters, the bark pH in both towns steadily converged in the reference period. An examination of pre-industrial lichen studies shows that in both towns the original state of lichen vegetation has not been restored yet.
Highlights
In the years 1970, 1980, 1985, 1995, 2005 and 2010, lichen mapping in the towns of Wetzlar and Giessen in Hesse was performed
The results show a marked increase in the pH of all the species of trees that are given (Tilia spp., Populus spp., Malus domestica) and in both investigated towns (Figure 4)
Conclusions regarding air pollution Both the results of the bark pH measurements and the results of the lichen surveys show the improvement of the air quality in the Hessian towns of Wetzlar and Giessen over a period of 40 years; they are estimated as being representative for large parts of Hesse
Summary
In the years 1970, 1980, 1985, 1995, 2005 and 2010, lichen mapping in the towns of Wetzlar and Giessen in Hesse was performed. Comparative assessments of the air pollution situation are hardly possible; as in previous studies, different methods have been observed, and the transfer to modern, regulated and standardized methods [1] fails as the original data are no longer available. The towns of Central Hesse, Giessen and Wetzlar, represent a positive exception from these points: they have been mapped repeatedly at irregular intervals since 1970, and the original survey data of the respective investigations are still available. The sole occurrence of this species indicates, by the standards of today's Association of German Engineers (VDI) guideline interpretation, an extremely high immission load with acidic pollutant gases - primarily SO2. Besides the recording of the lichen vegetation from 1970 in Giessen and 1985 in Wetzlar, measurements of the pH of the bark of the mapped trees were made, so that, in this case, a comparison with our current studies of 2010 was possible [4,5,6,7]
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