jessica Ledesma

Graduate Student, MS


Dr. Craig Rasmussen


Environmental Science


Effects of long-term stockpiling on soil quality and reclamation potential
for copper mine sites in semi-arid regions

A single copper mine can occupy thousands of acres of land for waste storage. This can greatly impact the biodiversity and health of surrounding native ecosystems. Mines typically cap this waste with 15-30cm of soil material to control dust emissions and enhance vegetation establishment during site reclamation. However, sourcing topsoil materials to reclaim these sites can be destructive. Thus, it is imperative to use efficient cover materials that facilitate successful ecosystem recovery while minimizing destruction of adjacent ecosystems. The objective of this research is to examine the effect of long-term stockpiling on topsoil quality in a semi-arid region by assessing soil health metrics associated with successful ecosystem recovery. For this purpose, two soil cores located on an Arizona copper mine were sampled from soil material surrounding native ecosystem that was stockpiled in 2007. The cores were drilled to 20 and 30 meters in depth and sampled every 76cm.  In total, 64 bulk soil samples and 192 microbial soil samples were collected. These samples were analyzed to understand the soil quality and variability within and between the two soil cores. Soil texture, general agronomic properties, plant micro and macronutrients, and soil DNA biomass were analyzed. Depth profile trends revealed that soil DNA biomass decreased below 1000 ng/g dry soil at around 5m in depth in both cores. In the North Core, %organic matter (OM), dissolved organic carbon (DOC), NH4, P, and Fe increased at ~20m in depth which suggests an anerobic effect with depth on nutrient composition. Similar patterns were found in the South Core for %OM, DOC, NH4, and Fe at ~10m in depth. Overall, this research will potentially provide insight on topsoil stockpiling management strategies for ecosystem regeneration on lands degraded by mine-waste deposition and mine operations.