Will tree colonisation increase the risks of serious performance loss of engineered covers under climate change in Québec, Canada?

Abstract

In Québec (Eastern region of Canada), some mine sites have been reclaimed with engineered covers to control acid mine drainage generation. Under humid climate, used covers are mainly oxygen barrier covers. Their performance is based on the maintenance of a high level of water saturation in cover layers that decreases oxygen ingress down to reactive mine wastes. After mine closure, natural colonisation of plant species adapted to current climate conditions takes place gradually on the covers. Plants, especially trees with deep rooting, can affect the water balance of the cover materials. If water saturation decreases in cover materials due to root colonisation, it can cause oxygen ingress to the mine wastes. Numerical models used to predict cover water balance integrate vegetation effects mainly through the use of leaf area index (LAI), root maximal depth (Rtmax), and root length density (RLD) as input parameters. By 2100, a northward shift of the distribution of some tree species is predicted from temperate to boreal regions of Canada because of climate change (CC). In this paper, the Lorraine abandoned mine site reclaimed with a cover with capillary barrier effect (CCBE) and surrounded by a boreal mixed wood forest was used as a case study. CC projections, woody species inventories, and bibliographical research of tree species distribution changes and associated values of key parameters were conducted. All the information collected, along with CC projection data, has helped anticipate potential effects on cover water balance components in the context of CC for the Québec region. At the Lorraine mine site, future dominance of shallow-and medium-rooted deciduous tree species and decline of shallow-and deep-rooted coniferous tree species with CC will have impacts on the CCBE water balance. Further insights are needed to model and integrate potential effects of CC on the evolution of LAI, Rtmax and RLD values of shallow-, medium-and deep-rooted species when assessing the efficiency of mine reclamation cover design over the long term. Preventive and/or remedial measures may be required to prevent cover performance decrease due to tree colonisation.