Evaluation of the Quality of Reclaimed Soils at Anglogold Ashanti Iduapriem Mines, Ghana

Abstract

The assessment of reclamation status must include soil biogeochemical indicators that are sensitive to management. This study was conducted in the Iduapriem concession, Tarkwa to determine the (a) biodiversity of the study sites, (b) characteristics of the soil profiles of the reclaimed sites and the natural forests, (c) quality of rehabilitated mined soils. Therefore, six mined sites viz B1 Pit (Site B), ITSF (Site C), OTSF (Site D), B1S/E (Site E-9), B2&3 (Site E-18), and B1N (Site E-21) under four different modes and varied ages of reclamation were selected for the study. The Neung natural forest (Site A) was used as the control site for the study. For the biodiversity assessment, the floristic and earthworm composition in each site was estimated using the Shannon-Wiener, Margalef’s, Pielou equitability, and the Czekanowski similarity coefficient indices. A 100 cm deep profile was dug at each site and samples were taken at 10 cm intervals. Each profile was described morphologically and their physicochemical characteristics were compared with the control site. Soils were also sampled from all selected sites at 0-20 cm depth using an auger for soil quality assessment. The collected soil samples were transferred to the laboratory and subjected to the physical, chemical, biological analyses and principal component analysis (PCA) to determine soil quality index. The highest Shannon-Wiener diversity index value of 3.13 was obtained at Site A (natural forest). However, at Site B had an index value of 2.64 which came close to Site A. Whereas Site C had an index value of 1.19, Site D had an index value of 1.62. Among the same mode of reclamation, Site E-9, Site E-18 and Site E-21 had an index value of 1.23, 1.82 and 1.76 respectively. Whereas a total number of 954 earthworms were collected from the study area, 30 were collected from Site A. A population of 540 earthworms were collected from Site B, 43 from Site C, while Site D recorded 129 earthworms. However, Sites E-9, E-18 and E-21 produced 6, 5 and 201 earthworms, respectively. The Shannon-Wiener earthworm diversity index was in order of Site B (0.89) > Site E-18 (0.82) > Site A (0.58) > Site D (0.57) > Site C (0.48). However, the index value for Sites E-18 and E-21 was 0 for each site. The use of heavy mining equipment in transporting, dumping and spreading the reclamation materials, compacted the soils. This resulted in higher bulk densities, poor soil structure and limited root distribution within profiles of the reclaimed sites. However, the reverse was the case in the natural forest. Except for the tailing provenance reclaimed sites (Sites C and D) that had a neutral pH, the other reclaimed soils and the natural forest soil were in the range of strongly acid to extremely acid condition. The natural forest recorded the highest soil organic matter, total carbon, total nitrogen. However, in the reclaimed sites, it occurred in the following order: Site B > Site E-21 > Site E-9 > Site E-8 > Site D > Site C. Considering the vertical cross section of the individual profiles of the reclaimed soils, it is clear to conclude that the similar and uniform properties observed from the reclaimed profiles is due to cumulative impact of anthropogenic activities rather than pedogenic. The, PCA selected bulk density, aggregate stability, CF, Exch. acidity, total P, C: N, Cmic and SFD as the final MDS. However, the SQI for the natural forest was 0.687. Whereas in the reclaimed sites, SQI was 0.527 at Site B, Site C had 0.197 and Site D had a quality index of 0.310. At Site E, the value of SQI increased with reclamation age which occurred in the following order: Site E-21 (0.589) > Site E 18 (0.424) and Site E-9 (0.320). The mode of reclamation had significant impact on the physicochemical and biological properties of the reclaimed soils than the age of reclamation. Hence a better performance of the conventionally reclaimed site (Site B) than the haphazardly reclaimed sites. The findings of the study indicate that topsoil management and replacement is very crucial in the recovery of degraded mined lands.