Hydrophysical Properties of Peat in Undisturbed and Smelter-Impacted Peatlands: Implications for Moss Recovery, Drought and Wildfire

Abstract

Peatlands are critical for global climate regulation storing approximately 500 Gt of carbon and accounting for 33% of global soil organic carbon. Regionally, these ecosystems provide essential wildfire resilience and are important pollutant sinks but degradation puts these key ecosystem services at risk. Smelting operations in Sudbury, ON, Canada, released approximately 12 000 t of particulate copper and nickel into the atmosphere between 1883 and 1969. Toxic metal and sulphur deposition on peatlands from smelting activities caused the widespread decline of keystone peatland moss species (i.e., Sphagnum) and altered peat properties. The changes in peat hydrophysical properties due to historical metal contamination likely reduce peatland resilience to drought and wildfires, thereby increasing the potential for toxic heavy metal remobilisation; however, these peat properties changes have yet to be quantified. We determine 1) how historical smelter pollution impacts peat hydrophysical properties by measuring bulk density, saturated hydraulic conductivity and soil water retention in the upper 40 cm of both undisturbed (located ~160 km outside the deposition region) and smelter-impacted peatlands, 2) use these data to explore the vulnerability of these peatlands to wildfires and drought and 3) assess the potential for natural Sphagnum moss recovery. Smelter-impacted peat had a significantly higher bulk density, lower macroporosity and saturated hydraulic conductivity that drove large differences in modelled soil water tension profiles during simulated drying events. These differences in soil water tension and retention profiles resulted in the smelter-impacted peat having a far greater proportion of the peat profile that would be susceptible to smouldering combustion than the undisturbed peat. Additionally, the smelter-impacted peat properties likely contributed to the limited Sphagnum moss recovery, while concurrently increasing drought and wildfire risk. As such, we argue that contaminated peatland restoration is necessary to enhance Sphagnum moss recovery to mitigate toxic metal remobilisation risk from drought and wildfire.