Mine reclamation and nitrogen cycling: Application of mine subsoil, soil amendments and native vegetation as tools for effective ecosystem reclamation

Mining is a strong contributor to Canadian and British Columbian economies. Mining yields raw materials without which human society would not be able to function. Also, this industry is a source of income for thousands of households. However, because of the large scale of operation, mining has an impact on landscapes and ecosystems including fragile and unique ones such as grasslands. This highlights the need for an effective and ecologically-based reclamation strategy. The reclamation of mine lands is a challenge because mine soils following mining activity are often deprived of organic matter, nutrient-poor, possess adverse physicochemical properties, and can be contaminated by heavy metals. Due to the large size, the capping of reclaimed land by topsoil is often not possible, the attention of reclamation practitioners has focused towards subsoil which is generated as a waste product and often stockpiled in large quantities. It is an open question whether mine subsoil can play a role of starting substrate for mine lands ecological reclamation. This is the overarching question of this thesis: can subsoil be transformed into operational topsoil? It is hypothesized that this process will not be successful if the proper nitrogen cycling is not fully restored as nitrogen is one of six elements called biogenic and is intrinsic to all living organisms. The objectives of this thesis were to investigate (1) whether subsoils collected from New Afton New Gold and Teck Highland Valley Copper mines were suitable to sustain a viable vegetation cover, (2) whether an application of biochar, woodchips, biosolids (nitrogen-rich) and a mixture thereof ameliorate subsoil futures and help in subsoil transformation, (3) whether nitrogen influences revegetation and what transformation this element passes on the way of its cycling during the early stages of reclamation. Two potting experiments were conducted to address the research objectives. The first one took place in the controlled conditions of a greenhouse and worked with native in BC graminoids and legume (nitrogen fixer). The second one was conducted in open-air conditions and worked with three native shrubby species including one non-leguminous nitrogen fixer. The results indicated that none of the analyzed mine subsoils, due to their low fertility and adverse physicochemical properties, was capable of sustaining viable vegetation when unamended. The situation changed when subsoils were amended by biosolids or a mixture. An addition of 25% of woodchips or 5% of biochar did not help. The vegetation response to nutrient input related to biosolids application was positive in the case of both mines, however, productivity on Teck Highland Valley Copper mine subsoil was significantly larger than productivity on New Afton New Gold mine subsoil in both experiments (experiment 1 ii Kruskal-Wallis p < 2.2e-16; experiment 2 Kruskal-Wallis, p = 1.7e-08). Physicochemical tests revealed that New Afton New Gold mine subsoil’s high pH and salinity posed a hindrance to overcome for vegetation growth. Additionally, throughout both experiments, the contents of total nitrogen, mineralizable nitrogen, and ammonium decreased, while the nitrate content increased. That in turn might indicate that in the early stage of reclamation, when biosolids are applied as a source of nitrogen, the nitrification step of the nitrogen cycle takes prevalence. Seven native plant species were used in this research and all demonstrated that they can cope with harsh growing conditions created by two mines’ subsoils, however, they need to be provided with initial nutrient sources. This research provided valuable information about subsoil, soil amendments, and native vegetation (including nitrogen fixers) to consider when undertaking mine lands reclamation.