Hydrogeochemical Characterisation and Water Quality Assessment of Streams Impacted by Agricultural Runoff in Uyo, Akwa Ibom State, Nigeria

Abstract

Agricultural runoff is a major global non-point source of water contamination, contributing substantially to nutrient enrichment, heavy metal loading, and hydrogeochemical alteration in freshwater systems, particularly in humid tropical regions. This study assessed the influence of agricultural activities on the water quality of three streams (S1–S3) within the Uyo Agricultural Zone of Akwa Ibom State, Nigeria. A total of 36 water samples were collected across wet and dry seasons from March 2024 to February 2025. Hydrochemical parameters (pH, Dissolved Oxygen, Turbidity, and Total Dissolved Solids), nutrients (NO₃⁻, PO₄³⁻, NH₄⁺), and heavy metals (Pb, Cd, Hg, As, Cr) were analysed using standard field measurements and FLAME AAS (Flame Atomic Absorption Spectrophotometry). Concentrations of NO₃⁻ (12–18 mg/L), PO₄³⁻ (2.5–3.8 mg/L), and NH₄⁺ (1.8–2.5 mg/L) showed clear spatial variation, with consistently higher values at S2, which is closest to major farmlands. Lead levels exceeded WHO limits at S1 and S2, while Cd, Hg, As, and Cr remained within permissible thresholds. Slightly acidic pH (6.5–6.9), moderate Dissolved Oxygen (4.8–5.2 mg/L), elevated Turbidity (10–15 NTU), and increased TDS (430–500 mg/L) indicated the influence of sediment wash-off and agrochemical inputs. Seasonal comparisons revealed increases in NO₃⁻ and Pb during the wet season, reflecting rainfall-driven mobilisation of contaminants. The results show that agricultural runoff significantly affects the hydrogeochemical characteristics and water quality of streams in Uyo, stressing the need for improved land-use practices, erosion control, and watershed-protection strategies.