Chromatic evolution, chemical changes, and biological colonisation in the quarry fronts of the Santullán limestone massif (Cantabria, Spain): implication for the mitigation of visual impact in mountain quarrying

Abstract

The visual impact of the chromatic contrast between quarry faces and rocky outcrops represents one of the prominent disturbances to natural environments. This study, therefore, aims to quantify color changes over time in quarries by analyzing three faces of an active limestone quarry in Santullán, Cantabria, that were exposed to atmospheric conditions in 1978, 2003 and 2021. To achieve this, the contribution of biological colonisation to natural darkening, along with the physicochemical changes occurring on the quarry faces, have been evaluated using scanning electron microscopy in secondary and backscattered electron mode, UV–Vis spectrophotometric techniques, Raman spectroscopy and XRD and XRF analysis. The analysis revealed that the color change was primarily due to microbial colonisation rather than oxidative chemical reactions. Although color change does not follow a direct and progressive relationship with exposure time, biological colonisation, identified primarily as microbial communities dominated by phototrophic microorganisms, shows a clear increase in microbial presence, bioalteration, and penetration into the rock substrate in older samples. The most significant visual changes appear to occur during the first years of exposure of the massif to atmospheric conditions.