Microalgae as biodeteriogens of stone cultural heritage: qualitative and quantitative research by non-contact techniques

Abstract

Biological colonisation of stone is one of the main problems related to monuments and buildings conservation. It is amply recognised that microalgae have the greatest ecological importance as pioneer colonisers of stone materials, conducting to aesthetic, physical and chemical damages. Their deterioration potential is related with their photoautotrophic nature, using the mineral components of stone substrates and sunlight as energy source without any presence of organic matter. Stone biodeterioration by microalgae has been assessed by several authors. Most of the employed methodologies for microbial identification and monitoring are timeconsuming and require extensive sampling. In addition, the scaffolding and sampling procedures required may also transform the researcher in a biodeteriorating agent itself. In this chapter, non-contact techniques for colonisation detection and monitoring are proposed in order to fulfil the mission of heritage preservation. In vivo chlorophyll a fluorescence and digital image analysis were applied to estimate microalgal biomass and to quantify coverage of limestone samples artificially colonised by algal communities. The results showed that Ançã and especially Lecce limestones were extensively colonised on their surfaces revealing significant epilithic growth, whereas Escúzar and San Cristobal limestones were endolithically colonised by photoautotrophic microorganisms. The easily handled, portable and non-destructive techniques proposed allow the understanding of stone biodeterioration processes avoiding contact and damaging of the objects, which ensures a wide field of application on cultural heritage studies and the design of appropriate conservation and maintenance strategies.