Recovery of smelter-impacted peatlands (Sudbury, Ontario): botanical and microbial community perspectives

Abstract

Over one century of mineral smelting activities in the Sudbury Basin denuded the regional landscape of vegetation near Sudbury, Ontario, previously (early 1960s) the once the world’s largest point source of SO2 and particulate Ni and Cu emissions. In 1986, fourteen years after the start of major local pollution controls, Gignac and Beckett reported that poor fen peatlands neighboring a Sudbury smelter contained flat, black, and barren peat, depicting severe pollutant stresses. I investigated the plant and microbial communities, and interrelated geochemical controls, in these severely smelter-damaged poor fens. Over the past 35 years Sphagnum moss, a keystone peatland genus, has re-established in poor fens as close as 4 km to smelters, whereas in 1986, Sphagnum was not observed until 12 km. Chemical analysis of the peat showed that total Ni and Cu concentrations in peat samples were lower than in 1986, and decreased with increasing distance from the smelter. As peatlands are globally important carbon sinks, with microbial communities mediating peatland C-cycling, I determined how smelter activity has altered peat moss and soil microbiomes. I showed that microbial community structure was controlled by plant species and microtopography in endophytic Sphagnum communities but was primarily influenced by metal contamination and pH in peat. After healthy Sphagnum and peat plugs were placed into a contaminated peatland. Sphagnum fuscum (a hummock species) and Sphagnum fallax (a lawn species) showed signs of successful establishment (expansion and new growth) after two years, suggesting that more efforts should be made to restore Sudbury’s peatlands. The transplant peat microbiome shifted towards a community structure mirroring the microbiome of the host peatland illustrating the central role of this genus as an ecosystem engineer. I conclude my thesis discussion that because Sudbury peatlands show signs of slow natural recovery and considering the results from the Sphagnum transplant study, that pollutant legacies are abating to the point that large-scale active restoration efforts can now begin.