Growth Responses and Iron Uptake in Sphagnum Plants and Their Relation to Acid Mine Drainage Treatment

Abstract

--Increasing interest in the use of sphagnum wetlands to treat acid mine drainage {AMD) has prompted study of the tolerance of Sphagnum species to the various constituents of AMD waters. In this study, s. fallax ands. benryense plants were grown in the laboratory for 33 days in syntheti~ bog water to which Fec1 2 was added to achieve Fe+ concentrations ranging from 0 to 10,000 mg/L. upon exposure to Fe concentra-tions~ 100 mg/L, both species exhibited a signi-ficant reduction in growth after 33 days relative to controls, but this reduction was proportion-ately less for s. fallax than for s. henryense. Final Fe concent'ration in the planr-tissue was negatively correlated with growth and chlorophyll concentration in both species, and greatly exceeded the total cation exchange capacity for Sphagnum, suggesting nutrient cation deficiency as a mechanism of Fe toxicity. Based on data from a previous study of net primary productivity of sphagnum species in Big Run Bog, estimates were made for Fe accumulation by the growing plants on an areal basis. Projected areal accumulation of Fe was greatest at high Fe treatment concentra-tions (1,000-10,000 mg/L) for both species, despite significant decreases in plant growth. These estimates reinforce the conclusion that Fe uptake by growing Sphagnum plants can play only a relatively minor role in Fe retention in wetland systems constructed for mine drainage treatment. Results of this study also indicate that the via-bility of Sphagnum wetlands constructed for AMD treatment may be dependent on the species com-position.