Deterioration of limestone walls in Jerusalem and marble monuments in Rome caused by cyanobacteria and cyanophilous lichens

Abstract

Hard limestone walls in Jerusalem and marble monuments in Rome were studied. An attempt was made to classify the principal biodeterioration processes in walls facing the prevailing wind and those which were protected from it. In Jerusalem, those that face the prevailing rain-bearing wind become populated by cyanobacteria and cyanophilous lichens. Within c. 100 years white walls are turned to grey or black colour by these organisms. Rain detaches rock particles from the vicinity of the microorganisms at a rate of 1 mm in 200 years. Dark patches on marble monuments in Rome indicate the presence of cyanobacteria. Such biological activity promotes detachment of particles by rain and accelerates weathering leading to pit formation. The estimated rate of pitting is 1 mm per 40 years in the Forum Traianum. To prevent the biodeterioration of limestone and marble monuments the habitats and ecological demands of the various microorganisms must be considered.