Evaluation of land reclamation practices at Anglogold Ashanti, Iduapriem Mine Ltd, Tarkwa.
Reclamation is a desirable and necessary remedy to return the mined areas to an acceptable environmental condition whether for resumption of the former land use or for a new use and to allow such lands to achieve their optimum economic value. The reclamation study was carried out to assess the land reclamation practices at AngloGold Ashanti, Iduapriem mine Ltd., Tarkwa in the western region of Ghana. The study was in two parts: a sociological survey and a field experiment. The survey was conducted in the 8 neighbouring communities namely: Iduapriem, Adieyie, Adisakrom, Abonpuniso, Techiman, Wangarakrom, Badukrom and Teberebie. The survey methodology comprised of interviews using semi-structured questionnaires, focus group discussions and personal observations. Ten(10) environmental experts of the mining company, Chiefs/Opinion leaders and the Community Relation Officer were interviewed. The field experiment was carried out using soils from the four reclaimed sites of different ages, an unclaimed site and the nearby Neung forest reserve (control) and these constituted the treatments. Soil samples were taken at the depth of 0 – 15cm from the four reclaimed sites, the unclaimed site and the nearby Neung forest reserve (control) with a hand auger and analysed for soil fertility parameters including heavy metal contaminants. The remaining soil samples for each site were put in plastic containers and arranged in a Complete Randomized Design with four replications on the field for testing their suitability for cultivation of maize (Zea mays) and cowpea (Vigna unguiculata). Four plastic containers each filled with the soil constituted a plot. Foliar analysis for nutrients and heavy metal contaminants, yield and other growth characteristics were measured for the maize and cowpea. The study from the sociological survey revealed that the mining company adheres to reclamation security agreement signed with EPA-Ghana in 2004 and the company won the best reclaim mine in Ghana for 2007. There was high community participation in the reclamation exercise ranging from weed and fire control, consultation, seedling establishment, security and maintenance of trial farms. Agroforestry multipurpose trees; Acacia magium, Gliricidia sepium, Senna siamea and Leucaena leucocephala are used in reclaiming mined out sites. The company uses the following reclamation processes and procedures to rehabilitate the disturbed sites: earthworks/slope battering, spreading of oxide material, spreading of top soil, construction of crest drains and broadcasting of cover crops to control run-off and erosion, tree planting and field maintenance. In the field experiment from 2yr old, 5yr old, 9yr old and 11yr old reclaimed sites of the company, the nutrient levels from the reclaimed sites soils were higher than the forest reserve (control). The reclaimed practices had significant effect on the pH of the soil such that, there is general improvement in the pH of the soils from the reclaimed sites compared to the forest reserve (control). The highest pH of 6.02 was recorded from the 9yr old reclaimed site with the least (4.01) from the forest reserve (control). The 9yr old reclaimed site recorded the highest percentage base saturation of 90.6 and the lowest exchangeable acidity of 0.39%. The concentration of nitrogen in the 9yr old (T4) and 11 yr old reclaimed (T5) sites (0.34%) and (0.38%) respectively were high. The highest P content (14.67mg/kg) which indicates a moderate level was recorded in the 11yr old reclaimed site soil (T5). The K content (40.28mg/kg) and (35.00mg/kg) for the forest site (control - T0) and the unclaimed site (T1) respectively were low but the reclaimed sites recorded moderate level of the K content ranging from 50.33mg/kg in the 2 yr old reclaimed site to 90.48mg/kg in the 11 yr old reclaimed site. The highest zinc content (36.67mg/kg) was recorded from the unclaimed site (T1) with the least (7.33mg/kg) from the forest reserve (T0) (control). Iron (Fe) was found to be in the highest concentration of 20915.7mg/kg recorded from the 2yr old reclaimed site soil. The P and Mg contents in the maize plant were above the average concentration (0.2%) sufficient for plant growth. Apart from the unclaimed site, the N contents in the maize and cowpea plants from all the sites were higher than the average (1.5%) for plant growth. Generally, heavy metal contents in the leaf tissue of cowpea were higher than that of maize. Apart from Cd and Pb which were within the critical concentration of 3(mg/kg) and 10(mg/kg) respectively, the remaining heavy metals (Mn, Fe, Zn, Cu, As) in the leaf concentration of cowpea were too high with Fe having the highest concentration of 20915.7mg/kg recorded from the 2yr old reclaimed site soil and hence very toxic to the crop. Growth characteristics (stem diameter, height, above and below ground biomass) of the maize and cowpea plants differed significantly (P < 0.05) in the different sites soils except in the below ground biomass (BG) and the number of effective nodules (ENOD) of the cowpea plant. The 9yr old reclaimed site recorded the highest of all the measured growth characteristics. The highest yields of 1800.5kg/ha and 791kg/ha were obtained from the 9 year-old reclaimed site for maize and cowpea respectively. These yields are equivalent to 1800kg/ha and 800kg/ha for maize and cowpea respectively that farmers get in that part of the western region of Ghana where the study was conducted.
A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi in partial fulfilment of the requirements for the degree of Master of Science in Agroforestry, 2010