In British Columbia, mine operators are required to reclaim disturbed land to a defined condition upon mine closure. One effective approach is to stockpile soil and its contained microbial communities prior to mining and redistribute the stored topsoil after mining has ceased.
Topsoil, the uppermost 20 centimetres of soil rich in organic matter, is host to most plant roots and is important in encouraging regrowth of native vegetation. Topsoil stockpiles can reach 5-10 metres depth and sit undisturbed for the duration of a mine’s operation. Few studies have been undertaken to identify changes to microbial health in these stockpiles over time and current land reclamation practices are generally based on financial and logistical constraints rather than scientific knowledge.
This project measured geochemistry and soil microbiota through DNA sequencing to establish the ‘health’ of soil stockpiles at New Afton Mine and QR Mill. It tested if the age or height of the stacks affected the health of the topsoil.
Mine reclamation developments are an investment in the long-term health of the land at mine sites. This research has generated information that can help guide more effective, socially acceptable and lower cost planning, implementation and management of mine reclamation projects.
Better understanding of the importance of biodiversity and ecosystem function as it relates to site restoration efforts is essential to developing mine operational strategies.
This project was undertaken through a Natural Sciences and Engineering Research Council of Canada Industrial Research Chair to Dr. Lauch Fraser (Thompson Rivers University) in partnership with Greater Vancouver Sewerage and Drainage District, Genome BC, Geoscience BC, New Gold Inc, Teck, Real Estate Foundation of BC, Arrow Transportation, Trans Mountain Corp and BC Cattlemen’s Association. Geoscience BC also participated in a second research project completed through this funding program: Biodiversity in Ecosystem Reclamation, Central Interior, British Columbia (2016-069).
This study took place at the New Afton Mine near Kamloops and the QR Mill near Quesnel. Both are in BC’s South Central Region.
How was the data collected?
Soil samples were collected from topsoil stockpiles at the New Afton (solid stem auger drilling) and QR Mill (excavator) sites in 2018 and 2019 respectively. Nearby grassland and undisturbed forested sites were used as reference sites for the projects. The elemental composition of the soil samples was measured at the Analytical Laboratory at the Ministry of Environment and Climate Change Strategy in Victoria, BC. The soil microbial community composition in each sample was characterized for both fungal and bacterial OTUs (operational taxonomic units) in the Applied Genomics Laboratory at Thompson Rivers University in Kamloops, BC.
What was Found?
A decline in nutrients and microbial diversity and an accumulation of metals, and beneficial, pathogenic, anaerobic, and rare microbial genera was found with increasing stockpile depth. The geochemical properties and microbial communities in the stockpiles, especially the deeper soils, varied from reference soils and global trends for soil bacteria and fungi, which may negatively affect the ability to restore the sites to a historical state.
Given the results detailed in this study, the potential of the topsoil after long-term storage is likely not enough to fully restore a functional and structurally representative native habitat at both mining operations without amendments. These stored soils will likely require enhancement prior to placement for reclamation to achieve historical conditions. Importantly, these results demonstrated the importance of interdependent ecological, geochemical, and biological processes, and the role of belowground processes in determining the success of restoration efforts.