Weathering rates of bedrock by lichens: a mini watershed study

Abstract

The chemical weathering rate of rock substrates by saxicolous lichens was measured quantitatively and compared with the weathering rate of bare rock in the Cone Pond area at Hubbard Brook Experimental Forest, USA. The experiments used mini watersheds (<1 m 2) on outcrops of mica–schist. A laboratory mini watershed experiment and a thin-section analysis were also conducted during the course of the study. Computed cumulative flux ratios of the weathering rate of lichen covered versus bare-rock mini watersheds for Mg 2+ (16±7) and Si (4±0.3) were significant. The rate of denudation of the rock was calculated to be higher for the lichen mini watershed than the bare-rock mini watershed. A laboratory mini watershed experiment demonstrated the same trend of higher elemental fluxes for the lichen mini watershed than the bare-rock mini watershed for K +, Mg 2+, Na + and Si. The weathering rind beneath the lichen was measured to be between 0.2 and 0.5 mm thick. These results show the significance of biotic enhancement of chemical weathering. This research also calculated the rate of denudation of the rock by lichens and supported the mini watershed studies as a reliable method to study the chemical weathering by lichens, bryophytes and plants in thin soil and alpine areas.