The effect of vegetation on porewater composition in a natural wetland receiving acid mine drainage

The effect of plant growth on surface and porewater concentrations of Fe, Mn, Cu, and S within a natural wetland receiving acidic spoil heap drainage was determined over a period of one year. Comparisons were made between unvegetated sites and those colonized by either Phragmites australis or Eriophorum angustifolium. The presence of vegetation increased surface and porewater concentrations of Fe and Mn in spring and summer largely due to the effects of higher evapotranspiration rates in vegetated areas. Microbiological processes were also thought to be important in controlling iron and sulfur concentrations at depth due to bacterial sulfate reduction and metal sulfide precipitation and iron and manganese concentrations close to the sediment surface due to bacterially mediated oxidation. These processes varied in importance with season due to changes in the dominant chemical and biological processes, although the complexity of the system prevented isolation of the principal mechanism involved.