Evaluation of some heavy metals and physico-chemical properties of soil under two sampling depths in Gambari Forest Reserve (GFR) , Ibadan, Oyo State, Nigeria.

Abstract

This study was carried out with the aim of determined the soil depth variations in heavy metals and some physico-chemical properties of soil depths sampled in Gambari Forest Reserve (GFR). It was examined with the purpose of evaluating the environmental impact of human activities on the Forest Reserve. Soil samples were collected randomly from eight plots within the forest at two different depth of 0-15 and 0-30 cm with the aid of soil auger. Systematic sampling design was used to lay two straight line transects, each of 1000 m long and separated by 500 m, in the reserve. Four Temporary Sample Plots (TSP) of size 50 m×50 m were laid along each transect at 250 m interval. Furthermore, a 6 × 6 m subplot was laid out at the centre of each plot. Samples of about 500 g each were collected in plastic bags and taken to the laboratory for analysis. The physico-chemical properties were evaluated using standard methods, while metal contents were conducted with flame atomic absorption spectrophotometer following wet acid digestion. Descriptive and inferential statistics were used for data analysis. The content of metals (mgkg^-1) gave the ranges: 3.02-5.92 Cd, 8.69-14.25 Cr, 1.39-1.67 Cu, 5.01-6.83 Mn, 13.37-14.25 Ni, 3.69-5.89 Pb and 1.59-1.75 Zn, with a variation pattern in order: Ni ˃ Cr ˃ Mn ˃ Pb ˃ Cd ˃ Zn ˃ Cu in both soil depths. With the exception of Cadmium, the degree of pollution varied with, by values that were far less than the upper tolerable limits set by Food and Agriculture Organization and World Health Organization for agricultural soils. Results show that sand had the highest % in soil of the area (92.34). Bulk densities were at ranges of (1.43, 1.45 and 1.23g/cm³) at the depth of 0-15 and 15-30, respectively. The textural classification for each depth of soil was Sandy-loam with percentages of sand (89.9-86.0), silts (10.94-4.41) and clay (5.68-3.03). Considerable spatial variations in contents were observed for all physico-chemical properties in all part of the study sites. GFR is relative nutritious and contain high amount of heavy metals. Therefore, it recommended that reserve should be enriched with tree and properly protected and monitored from encroachment of both human being and animals.