In situ microscopical diagnosis of biodeterioration processes at the convent of Santa Cruz la Real, Segovia, Spain

This report describes the in situ evaluation of biodeterioration processes occurring in the stone (granodiorite and carbonate) of the Convento de Santa Cruz la Real, Segovia, Spain. Scanning electron microscopy with back-scattered electron imaging (SEM–BSE) and X-ray microanalysis were used to examine stone samples from the convent. Free-living algae and fungi, lichen thalli, mosses, cyanobacteria and bacterial colonies were observed. Some of these organisms were located epilithically, while others were found to inhabit fissures or cavities inside the lithic substrate, a few of which showed an euendolithic ecological niche. Biogeomechanical and biogeochemical processes associated with the presence and action of lithobiontic microorganisms were detected, as well as evidence for the biomobilization of elements by epilithic and endolithic microorganisms. The relative contribution of each lithobiont to these biodeterioration processes were found to vary according to the type of stone and its position in the monument.