『Abstract
It has long been suspected that lichens increase the rate of
physical and chemical weathering of rock surfaces, thus playing
a role in biogeochemical cycles. However, the relative weathering
flux of elements from lichen-colonized rock versus bare rock has
been minimally studied; previous attempts to quantify the effect
of lichen-cover on weathering have focused disproportionately
on evidence from altered weathering rinds on basalt. Here, in
a field experiment on hornblende granite in New Jersey USA), we
measured the cumulative waterborne net efflux of five elements
over 31 days and six rain events, from multiple constructed miniature
watersheds consisting of either lichen-covered or exposed bare
rock. On average, lichen-covered watersheds showed approximately
double the silicon flux, and three times the calcium and magnesium
flux compared to bare-rock. Additionally, efflux of these elements
was higher in lichen-covered watersheds across all six rain events.
This suggests that lichens do indeed promote increased chemical
weathering compared to bare rock, thus likely increasing sequestration
of atmospheric CO2 under equal conditions
of atmospheric pCO2, temperature, and rainfall.
It was also observed that lichen-covered watersheds showed a 50%
reduction in iron flux, and had a greater ratio of calcium and
magnesium to silicon flux compared to bare-rock watersheds. The
possible causes of these patterns are discussed.
Keywords: Lichen; Xanthoparmelia plittii; Biological weathering;
Biotic weathering; Chemical denudation; Weathering flux』
1. Introduction
2. Materials and methods
2.1. Study site
2.2. Experimental watersheds and other collection apparatus
2.3. Sample collection and instrumental analysis
2.4. Calculations and definition of terms
2.5. Effect of lichen cover and other variables on elemental
efflux
2.6. Polyurethane barriers
2.7. Bedrock composition
3. Results
3.1. Differences between treatments
3.2. Net efflux on individual rain events
3.3. Effects of other variables on runoff concentrations
3.4. Effect of polyurethane barriers
3.5. pH
3.6. Rock composition
4. Discussion
Acknowledgments
References