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

Abstract This study aims to quantify the colour modifications for different time periods observed in three fronts of an active limestone quarry (Santullán, Cantabria), exposed to atmospheric conditions in 1978, 2003 and 2021. The visual impact associated with the chromatic contrast between quarry faces and rocky outcrops represents one of the main disturbances to natural environments. For this purpose, the biological colonisation contribution to the natural darkening, as well as the physico-chemical changes that take place on the front surfaces, have been evaluated by means of scanning electron microscopy in secondary and backscattered electron mode, UV-VIS spectrophotometric techniques, Raman spectroscopy and XRD and XRF analysis. The analysis showed that colour change was due mainly to biological colonisation and not to oxidative chemical reactions. While colour does not follow a direct and progressive relationship with exposure time, biological colonisation, identified as cyanobacteria and free-living fungi, shows in the older samples a clear increase in the presence of microbial communities, bioalteration and rock substrate penetration. The main visual changes seem to take place in the first years of exposure of the massif to atmospheric conditions.