Physicochemical Properties and Selected Heavy Metals in Tin-Mine Spoil Soils around Jos Plateau Nigeria
Abstract
The physicochemical properties and heavy metals in both vegetated and non-vegetated spoil soils in Jos Plateau were determined. Three dug soil profiles and thirty three composite soil samples were collected with auger at depths of 0 – 15cm, 15 – 30cm and 30 – 50cm and analysed using standard methods. The results showed mean value ranges of 4.58 – 5.28 pH, 0.09 – 1.46 Organic matter, 42 84% Sand, 6 – 46% clay, 5-29% silt, 0.022 - 0.110% total nitrogen, 14.80 – 41.44ppm available phosphorus, 3.13 – 5.00meq/100g exchangeable calcium, 1.45 – 2.35meq/100g exchangeable magnesium, 0.04 – 0.51meq/100g exchangeable potassium, 0.15 – 0.20meq/100g exchangeable sodium, 8.16 – 12.28me q/100g CEC126.80 – 778.33ppm Fe, 0.16 – 0.44ppm Al and 5.50 – 23.50ppm Mn. The soils were found to be predominantly Sandy Clay Loam, acidic and deficient in nutrients, Nitrogen, Phosphorus and Exchangeable Bases. The concentrations of most parameters were higher in the cultivated spoil soils than in the uncultivated spoil soils. Land amendment materials such as organic wastes and town refuse ash should be applied to the soils in the area.
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Introduction
Nigeria‟s tin mining industry is situated on the Jos Plateau more than 1300m above sea level.
Mining activities have been identified as a major cause of land degradation the world over (World Bank, 1995). The physical and chemical characteristics of mine soils affect reclamation efforts. These characteristics vary depending on the quality of the original soil, the amount and size of pulverized bedrock included in the spoil and the method of placement (Reuter, 2001). Generally, however, the properties of mine soils make them a poor medium for plant growth (Sengupta, 1993). This is because removal and crushing of bedrock exposes geologic material that is not stable at earth surface conditions and the alteration of this material impacts the chemistry of the environment (Reuter, 2001).
Mining activities have been identified as a major cause of land degradation the world over (World Bank, 1995). The physical and chemical characteristics of mine soils affect reclamation efforts. These characteristics vary depending on the quality of the original soil, the amount and size of pulverized bedrock included in the spoil, and the method of placement (Reuter, 2001). Generally, however, the properties of mine soils make them a poor medium for plant growth and natural recolonization on these soils is slow (Sengupta, 1993).
About 320km2 land area of the Jos Plateau has been degraded as a result of open cast tin mining since 1904. Only about 30km2 has been reclaimed thus leaving nea rly 90% of the affected area derelict to some degree and only little reclamation has taken place since 1982 (Alexander, 1992).
The reclamation strategy adopted by the MLRU was a straightforward strategy involving the leveling of the spoil mounds and the in filling of the flooded excavations with the intention of returning the land to immediate agricultural production (Wimbush, 1963). Reclamation was rendered more difficult because at the beginning of mining, no attempt was made to adopt the normal strip-mine policy of removing and storing separately top soil, sub-soil and overburden. Consequently, the spoil mounds comprise a complex mixture of these various strata, which produces extremely acid and nutrient deficient soil parent material (Alexander, 1992).
Open cast tin mining in the area, among other factors, has led to shortage of arable lands. Subsequently, encroachment into marginal lands and the use of unproductive soils for farming is commonplace. Alexander (1989) reported that population pressure and land shortage reduced the period of fallow or even caused complete abandonment.
This study will examine soil constraints to natural vegetation growth on the tin mine spoils of the Rayfield area and Barkin Ladi LGA, both within the Jos Plateau. The soil categories include: unreclaimed / non-vegetated spoils, unreclaimed / vegetated spoils, reclaimed / vegetated spoils, cultivated spoils and about seven decades undisturbed soils. This study is aimed to assess the physicochemical properties of non-vegetated tin mine spoil soils on Jos Plateau.
Conclusion
Whether vegetated or non-vegetated, the tin mine spoil soils of the Jos Plateau are acidic and nutrient-deficient. Although the cultivated spoils generally have higher values for most of the soil parameters, most of these values were below permissible limits.
The findings from this study have shown that cultivation is one way through which the “waste-lands” of the Jos Plateau tin mine fields can be better utilized. The soils need application of land amendment materials such as organic wastes (from plants and animals) and town refuse ash as the soil physico-chemical properties show that all the soils of the area are acidic and deficient in Organic Matter, Total Nitrogen, Available Phosphorus and Exchangeable Bases.