Speciation of Pb, Cu and Cd in Wildland Soil of (Oli Camp) Borgu Sector, Kainji Lake National Park

Abstract

The study carried out seasonal study of some potentially toxic heavy metals: Lead, copper, cadmium, chromium, Nickel, and zinc in soils was conducted in five different vegetation zones of (Oli Camp) Kainji Lake National Park at two different levels. The vegetations are Isoberlinia woodland (S1), Terminalia macroptera woodland (S2), Burkea African/Detarium microcarpum woodland (S3), Riparian forest (S4) and Diospyrus mespiliformis (S5). The average values recorded for the wet season at 0-15cm depth in mg/Kg were in the order S1: Cd (10.73±2.00), Cu (34.21±0.00), Pb (20.08±3.40), Cr (39.39±2.30), Ni (29.14±2.90), and Zn (16.63±0.90); S2: Cd (11.56±4.00), Cu (24.11±2.78), Pb (18.97 ±4.50), Cr (47.34±6.70), Ni (12.03±3.45), and Zn (85.07±1.40); S3: Cd (7.17±2.45), Cu (47.52±2.10), Pb (19.73±1.00), Cr (37.48±2.22), Ni (24.67±1.20), and Zn (12.51±0.90); S4: Cd (8.00±1.30), Cu (35.21±0.00), Pb (19.74±1.00), Cr (37.96±3.00), Ni (10.93±1.00), and Zn (19.44±2.30); S5: Cd (1.95±0.00), Cu (7.92±0.40), Pb (10.74±1.20), Cr (40.35±2.60), Ni (25.27±1.80), and Zn (211.35±4.30). Generally, the trend showed a decreasing order for the sub surface soil (15-30 cm). Thus, the mean levels for the wet season at 15-30 cm depth followed the order of Zn>Cu>Cr>Ni >Pb>Cd in the vegetations investigated. The metal concentrations during dry season decreased at both depths with the ranges: Cd (0.74±0.02 to 2.26±0.01); Cu (2.02±0.02 to 6.72±1.10), Pb (9.18±3.40 to 18.48±1.45) Cr (23.55±2.00 to 51.94±2.70), Zn (160.06±0.56 to 323.08±2.10), and Ni (14.03±0.50 to 34.69±1.00) mg/g. The physico-chemical parameters of the soils in the wet and dry seasons was indicated that pH, 6.65 to 6.95 and 5.3 to 6.7; conductivity, 10.00±2.50 to 101.50±2.12 µScm-1; organic matter, 1.79±0.30 to 2.64 ±0.51 among vegetations studied at 0-15 cm and 15-30 cm depths respectively; this trend is similar to that of the dry season. The range 1.32±0.25 to 2.11±0.06 were recorded against wet season at both depths. Generally, the speciation result revealed that the levels of these metals studied in both seasons were associated in the order: Residual > carbonate > Fe-MnO > Exchangeable > Organic > Water soluble fractions. The finding in this study has led to the better understanding of the metal levels and their sequential interaction with one another. This will aid in determining and to create awareness about the metal ion status of Oli Camp in Kainji Lake Nation Park to stakeholders in order to mitigate against metal pollution as it is barely monitored.