Enhancement of physical weathering of building stones by microbial populations

Two limestones from Cri tc, Greece and a dolomite from Mansfield, UK were s ubjected to combined microbial and physical weathering simulation cycles, i n an attempt to assess the contribution of each agent of decay. Sound stone discs were exposed to different temperature and wet/dry cycling regimes in volving treatment with distilled water or solutions of sodium chloride or s odium sulphate. Before the weathering cycles, half of the discs were inocul ated with mixed microbial populations (MMP), originally recovered from deca yed building stone of Portchester Castle, Hampshire, UK. The presence of MM P greatly accelerated the rates of deterioration of stone of all treatments , measured by weight change and alteration of hydraulic properties of stone . A combination of physical and biological processes significantly enhanced the extent of dec ay when compared with the physical or biological agents acting alone. Populations of heterotrophic, sulphur-utilising halotolerant and moderately halophilic bacterial populations remained large throughout t he experiment. Biofilms formed by populations of microorganisms were visual ised by staining and assessed by colorimetric measurement of total carbohyd rate in the stone substrate. The relative contribution of microbial and phy sical weathering to the process is discussed. (C) 2001 Elsevier Science Ltd . All rights reserved.