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ECOLOGICAL FOOTPRINT OF ARTISANAL AND SMALL-SCALE GOLD MINING ON SOIL AND PROVISIONING ECOSYSTEM SERVICES IN MPOHOR WASSA EAST AND AMANSIE WEST DISTRICTS, GHANA
Issues of impacts of small-scale gold mining activities on the environment continue to take a center stage in environmental discourse in developing countries more especially sub-Saharan Africa. This study was carried out to assess ecological footprint of artisanal and small-scale gold mining on soil and provisioning ecosystem services in the Mpohor Wassa East and Amansie West Districts, Ghana. Composite samples of soil and water were taken in selected artisanal and small-scale mining areas for analysis. A total of one hundred and sixty-two (162) soil samples including control soil sample were analyzed over a period of three-months. Seventy-five (75) and eighty-seven (87) composite soil samples were taken from Amansie West and Mpohor Wassa East Districts, respectively. In addition, twenty-seven (27) water samples including control were taken and analyzed during the entire study period. From Mpohor Wassa East water samples, the mean pH ranged from 6.5 to7.1; Electrical Conductivity (EC); 58.7 to 152.3μS/cm; Total Dissolved Solids (TDS); 33.3 to 101mg/L, Total Suspended Solids (TSS); 5.3 to 645 mg/L; Dissolved Oxygen (DO); 5.4 to 12.9mg/L, Biological Oxygen Demand (BOD); 1.0 to 1.7mg/L. The DO, BOD and EC in most sampling sites exceeded the WHO permissible limit. The EC, TDS, alkalinity, and salinity values, however, were all within WHO recommended limits. The results of analysis of the water samples from Amansie West were also as follows: pH; 4.6 to 7.8; EC; 42.7 to 484.8μS/cm; TDS; 25.3 to 221.2mg/L; TSS; 12.5 to 390.7mg/L, DO; 4.3 to 11.8mg/L; BOD; 1.4 to 2.5mg/L. Mercury, arsenic, cadmium and nickel in water samples at both Mpohor Wassa East District sampling sites and Amansie West sampling sites exceeded the WHO and EPA (Ghana) acceptable limits. The concentrations of the following heavy metals in soils; Fe, Hg, Ni, Cu, Pb, Cr and As were above the FAO acceptable limit for agricultural soils. This suggests (which specifically?) that artisanal and small-scale gold activities have impacted on the soil. The study further revealed that change in land use due to artisanal and small-scale mining activities significantly influenced the following ecosystem services; drinking water, wood fuel, medicinal plants, raw material for construction and food crop production. However, in this study, all heavy metals analyzed with Atomic Absorption Spectrometer had Threshold Exceedance Ratio (TER) less than the total concentration when extracted with nitric acid. This translates that limited soil function might not occur since the TER values are smaller compared to the total concentrations and could not limit the function of the soil for agriculture purposes however, the re-mobility percentage especially, Cu was high and had higher percentage mobility in all sampling sites above 20% which suggest that, Cu has a higher potential to remobilized into the soil structure when environmental conditions are favorable. The geo-accumulation index showed that the soils in both study districts are moderately contaminated. The overall conclusion is that artisanal and small-scale mining activities have impacted on provisioning ecosystem services in the two study areas. Efforts aimed at restoring the provisioning ecosystem services therefore need to be considered by relevant authorities. Recommendations made from the study include mandated agencies such as Environmental Protection Agency (EPA) and Ministry of Minerals and Land Commission should regulate the activities of ASGM to stop the discharge of poisonous heavy metals into soil and water bodies. Also, Phytoextraction ability plants such as Sun flower (Helianthus annuus), Cannabis sativa, Tobacco (Nicotiana tabacum), Maize (Zea mays) can be cultivated to demobilize Cu and Hg in the soil and this can be championed by EPA and the Ministry of Agriculture in Ghana. Lastly, it was recommended that the Forestry Commission, relevant stakeholders or NGOs should champion Land reclamation activities such as reafforestation and afforestation should be encouraged at the mined sites to revamp provisioning ecosystem services supply.
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