The Biogeochemical Response of Copper in Peat to Freeze-thaw Cycling

Freeze-thaw cycling (FTC) is an important process that affects the hydrological properties, redox conditions and microbial communities in northern peatlands. Copper (Cu) is a common mining waste that contaminates peatlands in northern Canada. The mobility of Cu in peatland is significantly affected by FTCs in addition to microbial activity. In this study, the impact of FTCs on Cu mobility in peat was examined from physiochemical and microbiological aspects. X-ray absorption spectroscopy (XAS) was used to determine the local structure of Cu at the molecular level. Changes in voids distribution and connectivity were measured using a microCT scanner. Microbial respiration was studied and compared between two incubation experiments. The Cu species was identified as Cu (II) in both frozen and unfrozen peat. The proportion of voids in peat increased after “hard FTCs”, but decreased in the “soft FTCs”. Soft FTCs significantly reduced the production of methane from microbial respiration in peat.