The Biogeochemistry of Metal-Contaminated Peatlands in Sudbury, Ontario, Canada

Abstract

Understanding the biogeochemistry of metal-contaminated peatlands is important for predicting the impact of mining and industrial activities on peatlands and downstream surface waters and for predicting recovery of previously impacted sites. The objective of this work was to characterize the factors controlling spatial and temporal variability in surface peat (0–15 cm) and pore water chemistry of 18 regionally representative peatlands in Sudbury, Ontario, Canada. The pollution gradient is clearly evident as Cu and Ni concentrations in surface peat are elevated close to the main Copper Cliff smelter. Surface peat also differs greatly in acidity (pH) and organic matter content among sites, and dissolved organic carbon (DOC) concentrations in pore water are positively correlated with peat carbon content. In addition, sites having surface peat that is more decomposed also have pore water DOC that is more humified. Pore water chemistry varies seasonally; samples taken in late summer and fall were characterized by higher SO4, and lower pH and higher concentrations of base cations and metals such as Ni, Co, and Mn compared with those in late spring that had higher DOC, higher pH, and higher concentrations of metals such as Cu and Fe. Despite the large spatial and temporal variability in pore water chemistry, soil-solution partitioning (K d) of some metals (Ni, Co, and Mn) can be explained by pH alone. Modeling soil-solution partitioning for these metals and Cu, Al, and Fe is significantly improved with the addition of SO4; dissolved organic matter quality and quantity and/or the δ18O signature of the pore water in regression models indicating several factors other than acidity has an influence on pore water chemistry.