Impact of seasonal flooding on the spatial distribution and hydrogeochemical behavior of heavy metals in topsoils of Ibaji, Nigeria

Abstract

Flooding is an important environmental phenomenon that influences the redistribution, concentration, and transport of heavy metals in agricultural soils, particularly within floodplain environments. This study evaluated the concentrations and spatial distribution of arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) in flooded and unflooded agricultural topsoils of Ibaji Local Government Area, Kogi State, Nigeria. Soil samples were collected from flood-affected farmlands and unflooded control locations and analysed using Inductively Coupled Plasma Optical Emission Spectrometry (ICP–OES) following acid digestion. The results showed considerable spatial variability in heavy metal concentrations across the study area. In flooded soils, concentrations ranged from 0.6–3.7 mg/kg (As), 0.1–3.6 mg/kg (Cd), 0–7.9 mg/kg (Co), 0.5–23.4 mg/kg (Cr), 0–30.4 mg/kg (Cu), 6.5–289.1 mg/kg (Mn), 1.1–96.5 mg/kg (Ni), 0.4–24.2 mg/kg (Pb), and 0–122.6 mg/kg (Zn). Mean concentrations in the unflooded control soils were 1.5 mg/kg (As), 2.05 mg/kg (Cd), 2.7 mg/kg (Co), 10.5 mg/kg (Cr), 6.1 mg/kg (Cu), 178.4 mg/kg (Mn), 48.8 mg/kg (Ni), 5.7 mg/kg (Pb), and 48.3 mg/kg (Zn). Spatial analysis revealed heterogeneous distribution patterns with localized enrichment zones, particularly for Ni, Zn, Cr, and Pb. Although flooded soils generally exhibited greater variability and localized enrichment of several metals, elevated concentrations of Cd, Ni, and Zn were also observed at one control location, indicating that factors other than flooding may contribute to metal accumulation. The findings suggest that seasonal flooding may influence heavy metal redistribution through sediment transport and deposition processes, resulting in increased spatial variability of metal concentrations in agricultural soils. Continuous monitoring and sustainable land management practices are recommended to minimize potential environmental and agricultural risks in flood-prone areas.