Metal accumulation by bryophytes in some zinc-rich blanket bogs, Selwyn Mountains, Yukon Territory

Abstract

Collections of Pohlia wahlenbergii, Leptobryum pyriforme, Philonotis fontana, and Drepanocladus aduncus were made at the XY Zn–Pb sulphide deposit, Howard's Pass, Y.T., Canada. Brilliant lime green growths of mosses flourish in hillside blanket bogs fed by Zn-, Pb-, and Cd-rich spring waters derived from faults which crosscut sulphide mineralizations. All species showed elevated levels of accumulation of these metals, but the concentration of Zn in the upper thalli was higher than Pb or Cd. However, the relative enrichments favour accumulation of Pb rather than Cd and Zn. The bryophyte D. aduncus is unusual in that it gathers cadmium in preference to Pb and Zn, according to calculated relative enrichment factors. The bog materials which provide the substrate for moss blankets are unusual in composition; more than 60% of the material comprises secondary Zn minerals, viz., zincic calcite ((Zn,Ca)CO3), smithsonite (ZnCO3), and wurtzite (ZnS), and the remainder is humified peat derived from buried moss strata. The end product of burial and replacement of decaying moss layers is the hydrated zinc silicate, hemimorphite (Zn4Si2O7(OH)2∙H2O), which results from the cell by cell replacement of moss fibre with complete preservation of the rhizoid structure.