Estudo pioneiro da restauração de solos minerados em uma cronosequência de 10,6 anos na mina de carvão de Moatize – Moçambique

Abstract

Opencast coal mining drives economic growth, however, accessing the ore reserves results in multiple damages. Monitoring reclamation includes analysis of soil attributes. In the Moatize coal region, located in central Mozambique, Africa, there is an extensive area impacted by opencast coal mining. The aim of this study was to evaluate the chemical, physical and biological attributes of minesoils that have been under restoration for 0.5; 1.4; 5.3 and 10.6 years at the Moatize coalmine. The soil chemical attributes analyzed included soil pH, nitrogen, phosphorus, magnesium, sulphur and potassium, cation exchange capacity, base and aluminum saturation and heavy metal content, as well as total organic carbon (TOC) stocks, TOC content and chemical fractionation of organic matter. The physical attributes included the assessment of soil density and porosity, while the biological attributes involved the abundance and diversity of soil organisms. The results were subjected to analysis of variance using the Kruskal-Wallis method (non-parametric test), followed by comparison of means using the Bonferroni (Dunn) test at 5% probability and Pearson's correlation (p<0.05). Regression analysis (p<0.05) was used to understand the restoration trends of the soil attributes assessed. During the recovery process, only the 10.6-year-old minesoil showed conditions close to those of the natural soil, with the exception of the biological attributes, which remained distinct compared to the natural soil in all minesoils, highlighting the positive impact of shrub species on soil revitalization. Specifically, in terms of physical restoration, the bulk density (Bd) in the 10.6-year-old minesoil was 1.41 g cm-3 . It is estimated that it takes approximately 2 years for the Ds of the minesoil to reach the level of the natural soil (1,35 g cm-3 ) and it was observed that the increase in Ma and the reduction in Ds over the chronosequence was associated with an increase in the TOC content and all its fractions. The TOC content evolved substantially during the years of minesoil restoration. From 0.5 to 1.4 years of restoration, the increase was 251%, while from 1.4 to 5.3 years it was 110%. In addition to the improvements in the stock of TOC in the minesoils over time can be that TOC has had a positive impact on the availability of nutrients and the significant advancement of all their chemical fractions. Over the chronosequence, metal content variations was observed in the minesoils with Cr, Zn and Mn showing a downward trend, while Pb, Ba and Cu showed an increase. The persistence of the adverse effects of mining activity, even after a period of 10.6 years, is evident in the restoration of soil fauna, mainly due to the negative correlation with heavy metals. This indicates a long period for the establishment of biological balance, even after improvements to the area's chemical and physical attributes.