An analysis of the element content of lichens from the Northwest Territories, Canada

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Abstract
The results of a survey of the element content of saxicolous and terricolous lichens collected from the Northwest Territories, Canada, are summarized. Fourteen lichen species were collected from 45 sites and the lichens were analyzed for 20 elements by instrumental neuron acivation and X-ray fluorescence. An enrichment factor (EF) was calculated for each element analysis. The elements Al, Cr, Fe, Na, Ti and Va and mean EF values of 1-5 for all species. These low EF values indicated that, relative to average values for crustal rock, there was no enrichment of these elements in the lichens concerned. For other elements (Cl, Pb and S) consistently higher EF values were obtained. These higher values were interpreted in terms of (a) different methods of element accumulation, (b) sources of elements both natural and anthropogenic other than crustal rock and (or) soil, and (c) marked deviations of the actual substrate concentrations from the average crustal-rock concentrations used. The underlying structure of the data from some species was investigated using ordination techniques. These techniques provided some description of the element associations within the lichen thallus. These element associations were examined in relation to sources external to the plant. A principal component analysis was carried out on the data for each of 3 spp., Cetraria cucullata, C. nivalis and Cladina stellaris. In all cases, the first 5 principal components explained 81-89% of the variation in the data. One component which had high weightings for Al, Sc and Va (with or without Fe, Ni and Ti) was common to all 3 spp. Similarly, a 2nd component with high weightings for Ca (with or without Mg and K) was a consistent feature of each analysis. These and other components were considered in the context of lichen enrichment from crust-derived particulates, the marine aerosol and certain anthropogenic sources. The high percentage of variation explained by the first 5 components strongly indicated that the major element sources contributing to this variation were considered. Nonmetric multidimensional scaling supported the principal component solution. There was considerable interspecific variation in the element content of lichens. Univariate analysis of variance did not show any significant differences between the element content of Cladina arbuscula, C. rangiferina and C. stellaris or any differences between Cetraria cucullata and C. nivalis on the basis of any single element. Multiple discriminant analysis showed that the species mentioned could be distinguished (.apprx. 90% discrimination) when all the elements were compared simultaneously. The discrimination between the Cladina spp. was based on the relative efficiency of these lichens in the accumulation of Fe, Sc, Ti and Va.