On the dual nature of lichen-induced rock surface weathering in contrasting micro-environments.

Contradictory evidence from biogeomorphological studies has increased the debate on the extent of lichen contribution to differential rock surface weathering in both natural and cultural settings. This study, undertaken in Côa Valley Archaeological Park, aimed at evaluating the effect of rock surface orientation on the weathering ability of dominant lichens. Hyphal penetration and oxalate formation at the lichen-rock interface were evaluated as proxies of physical and chemical weathering, respectively.

The susceptibility of weathered versus unweathered schist to biological colonization in the Côa Valley Archaeological Park (north-east Portugal).

This study addresses the primary and secondary bioreceptivity of schist used as a support for prehistoric rock art in the Côa Valley Archaeological Park (north-east Portugal) and provides some parameters that can be related to the risk of biologically induced schist weathering. Samples of freshly quarried and naturally weathered schist were characterized in terms of their intrinsic properties and maintained in controlled environmental conditions after inoculation with biofilm-forming cyanobacteria. The physical properties of the studied schist, as well as its abrasion pH, all varied according to the weathering degree of the samples and so did its susceptibility to colonization by biofilm-forming cyanobacteria.