On the Biotic Enhancement of Weathering by Lichens.
Following on from previous studies (e.g. Jackson & Keller, 1970; Aghamiri & Schwartzman 2002), in situ weathering rates of lichen-colonised and control rock surfaces were measured by determining the dissolved silicon (silicate, SiOX) concentration of run-off waters. In situ studies were conducted using two different methods on lichen-colonised concrete (aluminosilicate) and un-lichenised concrete (control). Ex situ experiments were conducted using a custom-built rainwater simulator, and lichenised and control rocks of ultramafic, sandstone, and turbidite type. Two different analytical methods were used to measure in situ SiOX, and different materials were tested for nutrient elements in order to determine the best materials for use in future studies. The in situ study revealed unusually high concentrations of silicon in run-off waters (mean = 143.5 µmol/l). The sample preparation for Inductively Coupled Plasma, Atomic Absorption Spectroscopy (ICP-AAS) has been implicated in causing these high concentrations which would have a bearing on the findings of previous studies (e.g. Aghamiri & Schwartzman, 2002), though these results have been corroborated by one previous study, Guzkowska, 1985 (Unpublished). A storm drain links the in situ study sites with a lake. Water samples were taken from this lake and an adjacent river, and analysed for SiOX. Samples from the river were an order of magnitude higher than those from the lake (P<0.01). This suggests that even though run-off waters are saturated with silicon, such run-off is a minor contributor to the silicon cycle. Drawing on all the areas of experimentation in this study, the role of lichens in weathering can, at best, be described as marginal, and is immeasurable on concrete. It is proposed that lichens contributed to the evolution of higher plants by making structurally useful compounds, such as SiOX, bioavailable.
BSc Dissertation, UEA, Norwich, 61
https://researchpages.net/esmg/people/michael-crouch/project/
Crouch_BSc_Dissertation_v3_.pdf