The variation in water content and in concentrations in trace metals in peat in different mire types

The mires in Ostrobothnia, Western Finland, can be classified into four types by trophic status: oligotrophic, oligo-mesotrophic, mesotrophic and meso-eutrophic mires. Geological investigations and analyses show that there are differences in the water content and in the concentrations of trace metals of peat between these mire types. The water content of peat is highest in oligotrophic mires, the average being 91.3%, and lowest in meso-eutrophic mires, where it is 86.4%. The water content of peat gradually decreases with an increase in the proportion of moss peat and in the degree of decomposition of peat from oligotrophic mires through oligo-mesotrophic and mesotrophic mires to meso-eutrophic mires. In all the mire types, Zn, Pb and Cd values are relatively high in peat, whereas Ni, Cr, Cu, Co and Mn show rather low concentrations in the uppermost peat layer. The concentrations of trace metals (Cr, Mn, Pb and Fe) in peat are highest in meso-eutrophic mires, but the concentrations of Co and Cu are highest in mesotrophic mires. The values of Zn are highest in oligotrophic mires and of Ni in oligo-mesotrophic mires. The concentrations of Cr, Cd, Mn, Fe and Pb gradually increase and those of Zn gradually decrease from oligotrophic mires through oligo-mesotrophic and mesotrophic mires to meso-eutrophic mires