Revegetation of Copper Mine Tailings Through Land Application of Biosolids: Long-Term Monitoring

The effects of biosolid amendment on revegetation of two copper mine tailing sites at a commercial copper mine were monitored. The two sites were amended with Class A biosolids in December 1998 (Site 1) and December 2000 (Site 2). Sites were located within 1 km of each other and were physically and chemically similar. At Site 1, biosolids were incorporated by disking into the tailings. At Site 2, biosolids were not incorporated, resulting in a 12-15 cm layer of biosolids on top of the tailings. The high moisture holding capacity of this layer of biosolids resulted in approximately twice as much soil moisture within the surface (0-30 cm tailing depth) at Site 2 than Site 1, when averaged over the period 2001-2007. This increased soil moisture persisted throughout the study period. The higher soil moisture at Site 2 resulted in significantly higher revegetation as estimated by Landsat data (Enhanced Vegetation Indices). It also resulted in enhanced microbial activities including denitrification activity, which caused soil nitrate concentrations at Site 2 to be minimal in December 2008. In contrast, nitrate levels at Site 1 at this time were excessively high. In addition, high tailing concentrations of Cu and Mo at both sites resulted in vegetation high in Cu and particularly Mo. In December 2008, 10 years after Site 1 was amended and 8 years after Site 2 was amended, the percent vegetative cover at the sites was 59.0% and 56.8%, respectively.