Assessment of Environmental and Anthropogenic Drivers of Heavy Metal and Hydrocarbon Pollution in Oguta Lake, Nigeria: Seasonal Variability and Comparative Analysis

Abstract

This study assessed the environmental and anthropogenic factors influencing heavy metal (HM) and total petroleum hydrocarbon (TPH) pollution in Oguta Lake, Imo State, Nigeria, with Abadaba Lake serving as a control. A mixed-method approach was adopted, combining field sampling of water and sediments over one year (April 2023–February 2024) with a questionnaire survey of 271 residents. Samples were collected in both wet and dry seasons and analysed following APHA (1999) standards. Descriptive statistics, Chi-square tests, and two-sample t-tests were applied to evaluate patterns and seasonal variations. Survey results indicated that oil and gas activities (38%), agricultural runoff (24%), crude oil loading (20%), and domestic waste disposal (18%) were the major contributors to contamination. Laboratory findings showed that TPH concentrations ranged from 0.07–45.20 mg/L, with no significant seasonal difference (p > 0.05). In contrast, heavy metals displayed notable variations: Pb (0.42–1.15 mg/kg), Cr (0.31–0.89 mg/kg), and Cd (0.02–0.11 mg/kg) were significantly higher in sediments during the dry season (p < 0.05), while Ni (0.15–0.44 mg/kg) was elevated in the wet season. Iron (Fe) remained consistently high across both seasons. The results highlight sediments as a more reliable indicator of pollution trends, underscoring the urgent need for stronger regulatory control of oil-related activities and improved waste management practices around Oguta Lake.