Storage and behaviour of As, Sb, Pb and Cu in ombrotrophic peat bogs under contrasting water table conditions

Concentration depth profiles and inventories of solid-phase As, Sb, Pb and Cu were determined in 210Pb-dated cores from an ombrotrophic peat bog in NW England. Cores were collected from the peat dome and adjacent to an eroding gully. Down-core distributions of As, Sb, Pb and Cu in the dome core are almost identical. The water table is close to the dome surface with only short-term draw-down. Under these conditions, As, Sb, Pb and Cu are immobile, allowing the reconstruction of trends in historical contaminant deposition. The peak in atmospheric deposition of As, Sb, Pb and Cu (4.59, 2.78, 147 and 26.7 mg m–2 y–1, respectively) occurred during the late 19th century. The 206Pb/207Pb ratio reveals that Pb deposition during this period was from indigenous and foreign sources. The mean water table is much lower at the gully-edge and there are pronounced inter-annual fluctuations. These conditions have not affected the integrity of the Pb and Cu records, but have caused post-depositional mobilisation and redistribution of As and Sb. Cumulative inventories show significant loss of As and Sb at the gully-edge site. Long-term water table draw-down in ombrotrophic peat bogs has the potential to alter the geochemistry and fate of previously deposited As and Sb.