Dark and Light Lichen Coloration and Basalt Weathering in a Cold Environment: Preliminary Results from Northern Canada

Abstract

Lichens are known to influence the weathering of rocks in natural or architectural settings. However, the specific influence of various lichen species on rock weathering remains to be understood especially in cold environments. The objective of this study is to understand the influence of various lichen species on the formation of secondary minerals in basalt. For 132 days, we recorded the temperatures every minute at the basalt/lichen interface of a light-colored lichen, Lecanora polytropa (Hoffm.) Rabenh., and a dark-colored species, Rhizocarpon geminatum Korb. to understand how lichen species influence thermal energy transfer. We also used scanning electron microscopy and Xray diffraction to determine the elemental and mineral composition of the products of basalt alterations. Our results show that during hot days (Regime 1), the rock/R. geminatum (dark-colored) interface has cooler temperatures than rock/L. polytropa (light-colored) interface as a result of the “necessity” to convect heat to the much cooler air in the environment. We believe that higher hyphal development in rock/L. polytropa interface results in a higher production of organic acids that lowers the activation energies of minerals present in basaltic rock, thus producing a higher rate of basalt weathering when compared to rock/R. geminatum interface. Our data also show the likely formation of whewellite (CaC2 O4 · H2 O) especially under L. polytropa. We believe that in our study, the dominant influence lichens have on basalt breakdown is due to biochemical processes.