Soil microbiological attributes indicate recovery of an iron mining area and of the biological quality of adjacent phytophysiognomies

Abstract

Mining activities modify the landscape and may have severe environmental impacts. The degree of recovery or disturbance of these environments must be determined, and microbiological indicators are most sensitive for this evaluation. The aim of this study was to evaluate the soil microbiological attributes of an area rehabilitated after iron mining activities and evaluate the adjacent phytophysiognomies. Soil samples were collected in a rehabilitated area revegetated with grass (RA) and in the phytophysiognomies of ironstone outcrops (IO), of neotropical savanna (NS), and of Atlantic Forest (AF) in two climate seasons (dry and rainy). Microbial biomass carbon, soil respiration, and enzyme activities (β-glucosidase, acid and alkaline phosphatase, arylsulfatase, urease, fluorescein diacetate hydrolysis) were determined, and the metabolic quotient (qCO2), the microbial quotient (qMic), and specific enzyme activities were calculated. Analyses of variance, means testing, and principal component analysis between the soil microbiological and physicochemical attributes were carried out. The microbiological indicators differed according to the type of phytophysiognomy and the season. Enzyme activities, microbial biomass, qCO2, soil respiration, and qMic were sensitive in indicating differences among the phytophysiognomies, as well as organic carbon, total N, Fe, Cu, and Al3+ contents, pH, potential acidity, cation exchange capacity, and clay and sand contents. The IO and NS phytophysiognomies exhibited the highest organic carbon and total N contents, whereas AF, NS, and IO exhibited the highest values of microbial biomass carbon. In both climate seasons, the AF exhibited higher values of soil respiration and enzyme activities. The Ironstone Outcrops exhibited high microbial biomass that was active in the processes of nutrient cycling, shown by its enzyme activities, whereas lower values of microbial biomass carbon and enzymes and higher values of qCO2 were observed in RA. Nevertheless, RA exhibited higher specific enzyme activities and higher qMic, indicating that the process of revegetation with grass favors activity of the microbial community, and promotes recovery of this area.