Soil Nutrient Dynamics and Potentially Toxic Elements of Sand Mining Impacted Agrarian Land in Obowo, Southeastern Nigeria

Abstract

The study assessed the effect of inland sand mining activities on the physicochemical properties and potentially toxic elements in soils in Umuna, Obowo LGA, Imo State, and Southeastern Nigeria. Triplicate soil samples were collected from soil depths ranging from 0-15, 15-30 cm) in eight traverse points and control. Points were designated soil sampling point (SSP) ranging between SSP1-SSP8 and control sample point (CSP1). The results of the particle distribution were in order of Sand ≥ Clay ≥ Silt, with Textural class ranging from sandy loams to loamy sandy. Chemical tracers: Soil pH ranged from 4.8 – 5.7 signifying moderate to strong acidity. The available P, Total N., SOC,SOM and BS ≤ control and Maximum Tolerable limits and FAO /World Reference Base. Effective cation exchange capacity (ECEC) (cmol/kg) (Ca2+, Mg2+, K+ and Na+), with mean Ca2+ 3.02, Mg2+, 0.64, K+ 0.09, Na+ 0.10 ≤ control respectively. Exchangeable acidity recorded 1.04 ≥ control, and CEC: 6.22 ≤ the control. Based on the ratings of soil nutrients for agricultural soil, the soil nutrients status of the sand mined sites ranged from very low to low status for total N(0.02 -0.04), avail. P (6.55-9.96), exchangeable K, (0.07-0.14), exchangeable Ca (2.25-3.55), and exchangeable Mg (0.25-0.85). Copper the mean value of 15.21, Lead: 12.20 and Cadmium (1.80) ≥ control (zero) above the FAO/WHO permissible levels respectively. Chromium (2.65) ≤ the FAO/WHO, limit. The potentially toxic heavy metals are in order of abundance in sand –mined soil: Cu ≥ Pb ≥ Cr ≥ Cd, with copper dominating the soil. The conservation of the area requires ecological restoration and regeneration of degraded mining site and the prohibition of mining activities as well as strict local control and enforcement of mining laws.