Nitrogen Dynamics As An Indicator Of Mine Waste Revegetation Progress

Abstract

Hard rock mining is a crucial industry but causes massive land degradation due to mineral excavation and residual waste deposition. Reclamation is accomplished through revegetating mineral waste in an effort to return mine sites to productive ecosystems. In arid and semiarid regions, revegetation requires low-nutrient waste rock to transition into to a plant-sustaining soil/substrate. This process is mediated by the establishment of fertility islands comprised of pioneer plant species. The objective of this research is to evaluate potential biogeochemical indicators of soil health that can be used to track improvements in waste rock fertility as a metric of revegetation progress, with a focus on nitrogen dynamics. Bulk samples of unseeded waste rock, seeded waste rock, and natural desert soils; as well as targeted samples of waste rock associated with shrub and grass rhizospheres were analyzed for DNA biomass content, amoA gene abundance to quantify ammonia-oxidizing bacteria (AOB), total nitrogen content, and ammonium content. Strong positive correlations were observed between plant cover and DNA biomass content, amoA gene abundance, and total nitrogen content. Shrub rhizospheres demonstrated a greater fertility island effect than grasses. Understanding associations between pioneer species establishment and enhanced waste rock fertility is critical to managing revegetation.