Descaracterização de barragens de rejeito de bauxita: como a indução da sucessão ecológica pode atuar na melhoria do substrato na fase inicial de descaracterização

Abstract

The closure of tailing dams is currently one of the main concerns related to the management of tailing dams in the mining sector, which can be noted by the recent changes in international standards and federal legislation on the subject. Applying revegetation as a technique for recharacterization of tailing dams is a great challenge, mainly because the organic matter content in the substrate is very low or non-existent. In this context, this experiment was conducted in three treatments that had the purpose of demonstrating the performance of the induction of ecological succession in three environments in bauxite tailings substrate with different conditions of green manure and addition of organic matter. In the T3 treatment (control) there was the planting of tree seedlings on the tailings; in the T2 treatment, in addition to tree planting, green manure with cover legumes was included; and in the T1 treatment, in addition to tree seedlings and cover legumes, organic matter from external sources was added. For the analysis of the induced succession process, parameters of soil physicochemical quality, development of the implanted vegetation and biomass generation were evaluated. The soil analysis of physical attributes showed no significant difference between the treatments for bulk density, total porosity and stability. All 3 treatments presented similar values of pH, m% and V%, with exceptions in the 0-5 cm layer. The T1 treatment stood out in terms of OM content and CEC values. The treatments T2 and T3 presented similar CEC values. T2 showed an increase in OM between the collections of 6 and 12 months after the implementation of the experiment. The highest biomass production of Crotalaria spectabilis Röth occurred at T1, however, Canavalia ensiformis (L.) DC. showed no significant difference between T1 and T2. The results of litter behaved according to the pre-availability of OM in the treatment, gradually increasing and with significant difference between T3, T2 and T1. T1 presented the highest mortality rate (Tm) of the species Hymenaea courbaril L., and there was no significant difference of Tm for the other species between the treatments. T2 presented the best results of admission of shrub and tree species. There was no significant difference in plants growth between treatments for all species, except for stem diameter of Inga edulis Mart., which were higher at T1. Throughout the experiment the majority of the seedlings had 50 to 100% of mature leaves and only Bixa orellana L. and Clitoria fairchildiana R.A.Howard came to flower. The induction of the ecological succession process through the treatments applied in this experiment was effective for the introduction of biological factors in the substrate, the improvement of chemical attributes in the surface layer and the settlement of tree species in the initial phase of bauxite tailing dams closure whose planned future use is reforestation.