Qualidade física em solo formado por rejeito de mineração do rompimento da Barragem de Fundão após processos de revegetação

Abstract

Mining, an intense activity in Brazil, generates environmental impacts, thanks to the by-products of the process, and the tailings are disposed of in dams built to contain this material for years. The Fundão dam (MG), which broke in 2015, was operated by the company Samarco and released 32 million cubic meters of tailings into the Doce River basin, causing a huge socio-environmental impact, reaching an area of about 1176 ha. Measures have been taken for restoration based on the implantation of grasses and legumes, with the aim of rehabilitating the affected areas, resulting in the formation of Technosols, from sediment deposits, and particularly by the action of roots and organic remains left by growing vegetation. Thus, the objective of this work is to evaluate the contribution of different plants in the increment of organic matter and structural improvements in these Technosols. The Technosol samples were collected on the banks of the Gualáxo do Norte river in the municipality of Mariana -MG, whose mining waste formed a layer superior to 1 meter and was revegetated in one of the areas with a mix of grasses, mostly consisting of Paspalum notatum, and another area of Technosol revegetated with Cynodondactylon grass. Another study was carried out on samples from previous research by Zanchi et al., 2020, whose material underwent treatments in a greenhouse, in 4 treatments with herbs, namely: Urochloaruziziensis; U. ruziziensis in association with Crotalaria spectabilis; U. ruziziensis in association with Guizotiaabyssinica; U. ruziziensis in association with C. spectabilis and G. abyssinica and as a reference the uncultivated tailings. Later, a tree species (Enterolobiumcontortisiliquum) was incorporated into these samples. Evaluations of physical quality indicators of the Technosol were carried out, namely: physical-water analysis (water retention, soil density, available water capacity, aeration capacity, S index, total porosity, pore distribution and resistance to penetration); granulometric evaluation with sand fractionation; particle density; aggregate stability index; and evaluation of the organic carbon content. Analyzes of variance were performed on the data and means were compared using the Scott-Knott test (p ≤ 0.05). A difference can be seen in the behavior of the CRA and the modeling of the IHO graph. For the indicators derived from the CRA, lower S, CA, PT, IEA, and CO index values were found for the waste compared to the cultivated treatments, in addition, this one had a lower content of large and medium macropores and mesopores and higher values of micropores, associated with the highest DS value, still comparing the treatments. It was also observed by the IHO modeling graph, that the CAD for the plants was more expressively restricted by the aeration porosity and by the resistance to penetration by the roots, compared to the cultivated treatments. Thus, through the indicators, improvements were observed in the physical quality of the Technosoil after the rehabilitation process of the area covered by tailings from the dam, using plants with potential.