Chemical and physical properties in degraded areas at the Moatize coal mine in Mozambique: An overview of the first decade of tree-driven restoration

In the Moatize mine, tree species have been used for the coal minesoil restoration for more than 10 years. Nevertheless, the effects of such revegetation on chemical and physical properties of Moatize minesoils remain unknown. Here we present a pioneering 10.6-year chronosequence study aiming to monitor Moatize minesoils fertility, organic carbon stocks, and porosity, as well as interrelations of these properties. Furthermore, a natural (unmined) soil was sampled for comparison to provide insights into the reintegration of minesoils into the environment. We hypothesized that the fertility, organic carbon stocks, and physical properties of the minesoils improve with increasing restoration time but remain inferior to those of the unmined soil, likely due to the short revegetation period (10.6 years). The study was carried out in the Moatize coal mining area in Mozambique. In 2023, soil samples were collected from the 0.00−0.10 m layer in three 100 m transects, totaling 12 replicates per site, and chemical and physical properties were determined. Minesoils exhibited similar and strong acidity (pH <5.0) until 1.4 years, while from 5.3 to 10.6 years, they exhibited intermediate (5.14) and moderate (6.14) soil pH. Soil organic carbon stocks doubled in minesoils between the initial (until 1.4 years) and the final phase of evaluation (10.6 years). The positive effect of revegetation is also evident in the increase in macroporosity of the minesoils over time. The minesoil with 10.6 years of restoration presented properties very close to those of the unmined soil. However, we reinforce the need to monitor these minesoil properties in the long term to certify the successful integration of the mined land into the landscape.