Technosol evaluation for mine site reclamation in the Boreal Shield

Abstract

Technosols, soils substantially influenced by human activity, are often found on former mine sites. In some cases they develop as a result of natural processes on abandoned sites; in others, they are intentionally manufactured as part of the mine’s reclamation program. In this study Technosols with either 40% woody residuals and 60% mine rock or 80% woody residuals and 20% mine rock were constructed and placed over mine rock lysimeters in either 30 cm or 60 cm layers to evaluate their potential for use in the reclamation of a gold mine in the Canadian boreal forest. The Technosol plots were constructed in summer 2012 and have been continuously monitored for water chemistry, soil microclimate, and vegetation health. In 2016 soil pits were excavated to examine the physical, chemical, and microbial development of Technosol profiles. The high organic Technosols had higher concentrations of bioavailable nutrients, reduced availability of Mo and Cd, less extreme soil temperatures, increased soil moisture, and reduced soil pH compared to the low organic. In all Technosol plot water samples pH was between 7 – 8, high levels of DOC were measured, and no elements exceeded site compliance limits specified by the Ontario government. Little profile development was observed in the Technosols, but there were differences between comparison field and forest soils in terms of chemistry and microbial functional diversity. Green alder (Alnus viridis subsp. crispa) grew well on the Technosol plots, but bearberry (Arctostaphylos uva-ursi) struggled and after two years almost complete mortality was seen. This is likely due to a combination of factors including high soil pH, low moisture, and low nutrient availability in the Technosols. Overall the high organic Technosol appears more suitable for reclamation, and green alders are a good choice for initial planting.