Spatial distribution of copper, organic matter and pH in agricultural soils affected by mining activities

The Aconcagua River Basin, located in north-central Chile, is an important agricultural region of the country. However, several copper mining industries are also located in this basin. A total of 103 topsoil samples were collected at varying distances from mining industries. There were no statistically significant differences between the sampling areas with regard to organic matter content and copper concentration. However, the sampling areas were significantly different with regard to soil pH. Soils of the Putaendo sampling area exhibited the lowest pH values (mean of 6.3), while the highest pH values (mean of 7.1) were measured in the Catemu - Chagres sampling area. In the sampling areas where mining activities were absent, the total copper concentrations ranged from 70-155 mg kg ^-1. These concentrations are a result of the geological setting and/or of applications of copper-containing fungicides. High copper concentrations (above 700 mg kg ^-1, with a maximum of 4000 mg kg ^-1) were generally observed near mining activities or in areas where mining activities were located nearby and upstream. In these sampling areas, the copper concentrations differed by an order of magnitude in nearby locations. These high and heterogeneously-distributed copper concentrations most likely resulted from either modern or former mining activities.