No abstract

The ongoing global deforestation resulting from anthropogenic activities such as unsustainable agriculture and surface mining threatens biodiversity and decreases both soil carbon and above-ground biomass stocks. In this study, we assessed soil properties and below- and above-ground biomass attributes in a restored former gravel mine area in Ghana two decades after active restoration with potted plants and fresh topsoil. We compared conditions to four alternative land-use types (unrestored abandoned gravel mine, arable land, semi-natural forest, and natural forest) representing pre- and post-disturbance as well as natural reference states. We hypothesized that soil properties and related levels of below- and above-ground biomass in the restored area share similarities with the natural reference systems and thereby are indicative of a trajectory towards successful restoration. Eight replicated subareas in each land-use type were assessed for a set of soil parameters as well as below- and above-ground biomass attributes. The soil properties characteristic for the restored area differed significantly from pre-restoration stages, such as the abandoned gravel site, but did not differ significantly from properties in the natural forest (except for bulk density and base saturation). Above-ground biomass was lower in the restored area in comparison to the reference natural forests, while differences were not significant for below-ground biomass. Silt and effective cation exchange capacity were closely related to above-ground biomass, while below-ground biomass was related to soil organic carbon, bulk density, and potassium concentration in soils. Our results suggest that major steps towards successful restoration can be accomplished within a relatively short period, without the wholesale application of topsoil. Improving soil conditions is a vital tool for the successful development of extensive vegetation cover after surface mining, which also affects carbon sequestration by both above- and below-ground biomass. We emphasize that the use of reference systems provides critical information for the monitoring of ecosystem development towards an expected future state of the restored area.

Topsoil is a valuable resource and regarded as the most critical and key component in any successful revegetation following mining activities. Consequently, salvaging and stockpiling topsoil for use in future reclamation is encouraged in mine operations. Studies have, however, demonstrated topsoil stockpiling has adverse impacts on soil properties and that stockpiled topsoil would require organic amendment to promote plant growth. This study was therefore undertaken with the hypothesis that (a) topsoil stockpiling as practiced at Newmont Ghana Gold Limited has adverse impacts on soil properties and (b) amending stockpiled topsoil with organic materials, composted sewage sludge and poultry layer manure, promotes the survival and growth of planted trees. A waste rock dump measuring 36m by 45m was graded and covered with a 70 cm layer of stockpiled subsoil followed by a 30 cm layer of stockpiled topsoil. Soil samples, with three replications, were collected at random from the experimental site and from a nearby un-mined, agricultural site used as reference, for determination of pH, nutrients, organic matter, electrical conductivity, effective cation exchange capacity, base saturation, bulk density, and texture. Poultry layer manure (PLM), composted sewage sludge (CSS), and no amendment (control) were the treatments. Pottedseedlings of five forest tree species; Terminalia superba, Terminalia ivorensis, Mansonia altissima, Kola gigantea, and Cedrela odorata; were planted in May 2016, followed by application of 1 kg and 0.5 kg (dry weight) of the PLM and the CSS respectively, per tree. Diameter and height data of all planted trees and number of surviving trees were collected twice to determine tree growth and survival. Statistical analysis revealed that topsoil stockpiling did not have any significant adverse impact on the measured soil properties, compared with the reference plot. One-way ANOVA combined with LSD and Duncan post-hoc tests (α = 0.05) also indicated no significant influence of organic amendments on tree growth. Competition from herbaceous plants due to ineffective weed control was observed to be the main driving factor hindering survival and growth of planted trees. Further study to compare planting the intended tree species concurrently with ground cover species in the first growing season combined with adequate weed control to influence tree growth and survival at the site, to the application of organic amendments is warranted.

Background: Despite the key role topsoil plays in reclamation, there are situations where topsoil is in deficit or unavailable, especially at degraded and abandoned mine sites in Ghana. The sites pose serious ecological and safety risks, underscoring the urgent need to finding alternative substrate for restoration. This study investigated the feasibility of using amended-subsoil as topsoil substitute for reclamation. The hypothesis was that amendment of stockpiled-subsoil with poultry manure positively influences tree growth and ground vegetation cover (GVC), which promote better soil stabilization at degraded mine sites. A graded waste-rock dump was covered with a 70 cm layer of the stockpiled subsoil at Newmont Ghana Gold Limited. Two experimental plots (24 × 15 m) were established with the treatments poultry manure (PLM 23 t ha-1) and control (no PLM), followed by seeding of Cowpea (Vigna unguiculata) and planting of potted-seedlings of five forest tree species. The Laser-point-quadrat method was used to estimate GVC, whereas erosion was visually observed. Diameter and height data of planted trees and surviving numbers were collected.Results: There was significant increase in tree growth and in GVC for the poultry manure treatment compared to the control. The manure provided sufficient nitrogen to overcome nitrogen deficiency and facilitated quicker and stronger vegetation growth that yielded superior soil stabilization.Conclusions: The findings demonstrate the potential of manure application in promoting successful restoration of the many degraded and abandoned mine sites in Ghana to productive uses.