Post-mining Nutrient Depletion of Bauxite Overburdens in Jamaica: Storage Methods or Subsoil Dilution?

Abstract

Rapid degradation of disturbed soil from a karst bauxite mine in Jamaica was recorded. Substantial macro-nutrient losses occurred during a short (1 month) or long (12 months) storage of the replaced top-soils during frequent wet/dry changes. The results suggested very high rates (>70 % in the first year) of soil degradation from storage, alongside moderate rates (30 %) within the same storage dump. However, higher levels of soil organic matter (SOM) were indicated just below the surface, compared with the surface horizons. It was unlikely that under a high leaching humid tropical rainfall regime, natural degradation processes could have re-emplaced such material firmly intact in the 15–30 cm zone. It was therefore concluded that these SOM anomalies were due to mechanical dilution of surface soil with sub-soil material during overburden removal and emplacement rather than from long storage. Increasing the soil organic content during storage could be one corrective approach. However, it is far less costly to exercise greater care to apply more precise overburden removal and emplacement techniques initially, than it is to correct the results of top-soil contamination with sub-soil. Although this study was limited to one mine, in the context of imminent large-scale mining expansion and current practices, further investigations are needed to accurately ascertain the proportion of similar sub-soil contamination in other bauxite-mined sites.