Differences in elemental composition of tailings, soils, and plant tissues following five decades of native plant colonization on a gold mine site in Northwestern Québec.

Mining activities have significant environmental impacts, such as the production of acid mine drainage and the typical absence of vegetation on mine tailings whose absence can facilitate the migration of metals to adjacent ecosystems. We investigated the metal and metalloid composition of plants and substrates on, and near a former gold mine site to understand elemental dynamics in such environments. A mine tailings deposit rich in Mo and As in Northwestern Québec was studied following the natural colonization of the deposit by boreal plant species. The site and surrounding forest were categorized into 6 vegetation density classes (VDC) to determine if and how vegetation density, and plant elemental composition, and soil properties were linked. Macroelemental composition of plant tissues (P, K and Ca) was relatively stable, despite differences in macroelemental levels of substrates between different VDC (with lower macronutrient levels associated with less dense areas), indicating the adaptability of the three species studied (Alnus incana spp. rugosa, Betula papyrifera and Picea spp.). Results showed that across a wide range of substrate properties, it was plant species and density that explained metal and metalloid composition in plant tissues (leaves, stems, and roots), while the main environmental determinants for this were VDC, pH, Ca and Cu. Increasing vegetation density was associated with decreasing As and Mo concentrations in substrates. This study sheds light on the plasticity of alder, spruce and birch growing on mine sites, allowing us to better understand elemental dynamics on such sites, and ultimately improve their management.