The impact of drought and air pollution on metal profiles in peat cores

Peat cores have long been used to reconstruct atmospheric metal deposition; however, debate remains regarding how well historical depositional patterns are preserved in peat. This study examined peat cores sampled from 14 peatlands in the Sudbury region of Ontario, Canada, which has a well-documented history of acid and metal deposition. Copper (Cu) and lead (Pb) concentrations within individual peat cores were strongly correlated and were elevated in the upper 10cm, especially in the sites closest to the main Copper Cliff smelter. In contrast, nickel (Ni) and cobalt (Co) concentrations were often elevated at depths greater than 10cm, indicating much greater post-depositional movement of these metals compared with Cu and Pb. Post-depositional movement of metals is supported by the observation that Ni and Co concentrations in peat pore water increased by approximately 530 and 960% for Ni and Co, respectively between spring and summer due to drought-induced acidification, but there was much less change in Cu concentration. Sphagnum cover and 210Pb activity measured at 10cm at the 14 sites significantly increased with distance from Copper Cliff, and the surface peat von Post score decreased with distance from Copper Cliff, indicating the rate of peat formation increases with distance from Sudbury presumably as a result of improved Sphagnum survival. This study shows that the ability of peat to preserve deposition histories of some metals is strongly affected by drought-induced post-depositional movement and that loss of Sphagnum due to air pollution impairs the rate of peat formation, further affecting metal profiles in peatlands. [Display omitted] •Lead and Cu is enriched in surface peat close to Sudbury.•Nickel and Co exhibit variable depth profiles in peat cores.•Nickel and Co concentrations in peat pore water increase greatly in the summer.•Greater post-depositional movement of Ni and Co in peat cores•Loss of Sphagnum due to air pollution lowers rate of peat formation.