Investigating biogeochemical signatures in the lichen Parmelia sulcata at Burnham Beeches, Buckinghamshire, England

Abstract

Biogeochemical signatures were compared in ‘living’ and ‘dead’ Parmelia sulcata samples with their oak bark substratum. Eighteen elements reached maximum concentrations in ‘dead’ lichens, at lower concentrations than reported from industrial regions. High N concentrations in ‘dead’ lichens confirm exceedances of critical levels established for deciduous woodlands, supported by alien algae and ‘nitrophytic’ lichen colonization. Negative δ¹⁵N values recorded in lichen samples indicate N originated mainly from ammonia. Less negative δ¹⁵N values in healthy samples near busy roads suggest local NO_x accumulation by Parmelia. Higher δ¹⁵N values in bark may result from different processes. Twenty-eight elements reach higher concentrations in healthy lichens near roads carrying higher traffic volumes. Thirteen elements correlate positively with lichen δ¹⁵N, suggesting that δ¹⁵N is a powerful indicator of the balance between agricultural and vehicular N influx. Maximum Ca and Sr concentrations recorded in bark and their spatial distribution suggest a local geological origin. High concentrations of Ga, Ba, Pb and Ni bark contents testify to a previous pollution legacy, including that from petrol which carried higher lead concentrations than today. Mn concentrations are higher than reported from other studies and show no clear relationship with local roads. Mn is known to limit lichen diversity and health in coniferous forests in US and Germany, but not yet in deciduous woodlands. Current atmospheric conditions and the former pollution legacy must be understood to conserve epiphytes and for biomonitoring.