Iron ore mining areas and their reclamation in Minas Gerais State, Brazil: impacts on soil physical properties

Abstract

Plant cover acts to maintain the balance between soil chemical, physical, and biological attributes, as well as superficial soil protection. The aim of this study was to evaluate the impacts of iron ore mining and their reclamation on soil physical properties and soil visual quality in Fort Lauderdale Municipal Park and Serra do Curral Municipal Park, Iron Quadrangle (Quadrilátero Ferrífero), Minas Gerais State, Brazil. The evaluated areas varied in relation to the post-mining condition, natural revegetation (NR), an area with gully erosion (GA) and area under eucalyptus revegetation (ER) and native vegetation cover, rupestrian field (RF), and seasonal semi-deciduous forest (NF). The main soil physical attributes evaluated were: soil organic matter (SOM), geometric mean diameter (GMD), weighted mean diameter (WMD), bulk density (Bd), air capacity (ACb), plant-available water capacity (AWC), relative field capacity (RFC), and visual soil quality assessment. In addition to the impacts on the landscape, with removal of vegetation and soil cover, iron ore mining process impacts soil physical quality measured through porosity and aggregation properties and therefore could impact ecosystems services. Areas of iron post-mining that are not restored can develop gully erosion. NR shows high erosion risk inferred through aggregation indicators (GMD = 3.84 mm; MWD = 3.04 mm), despite similar soil organic matter content and higher plant-available water and air (NR [AWC = 0.102 m3 m−3; ACb = 0.328 m3 m−3], NF [AWC = 0.062 m3 m−3; ACb = 0.202 m3 m−3]) compared with NF (GMD = 4.77 mm; MWD = 4.56 mm). ER had similar soil structure stability compared to NF as well most of the porosity indicators, which is associated with the higher soil organic matter. Soil visual assessment alone was not able to characterize the soil physical quality, mainly in the post-mining areas, because it was designed for agricultural soils.