Spatial and Temporal Variation in Dissolved Oxygen Levels in Oguta Lake, Imo State

Dissolved oxygen is a fundamental parameter of aquatic ecosystem health, and its spatial and temporal variability in lakes reflects the interplay of biological, physical, and chemical processes. This study examined the patterns of dissolved oxygen variation in Oguta Lake, Imo State, South East Nigeria. Dissolved oxygen was measured at surface, mid-depth, and bottom water layers at five stations across the lake during morning, afternoon, and evening hours over a period of six months. Simultaneously, water temperature, pH, transparency, chlorophyll-a, biochemical oxygen demand, and nutrient concentrations were measured. Thermistor chains were deployed at two stations to provide continuous temperature and dissolved oxygen profiles during selected 48-hour periods. Dissolved oxygen concentrations showed marked diel variation, with lowest values recorded in early morning hours and highest in the late afternoon, reflecting photosynthesis and respiration cycles. Vertical stratification was most pronounced during the dry season, with hypolimnetic oxygen depletion recorded at three of five stations. Shallow inshore areas supported higher oxygen levels than deep central zones. Biochemical oxygen demand was positively correlated with phytoplankton biomass, indicating productivity-driven oxygen demand. Stations near domestic sewage inputs showed chronically depressed oxygen levels. Pearson correlation and multiple regression analysis confirmed that water temperature, biochemical oxygen demand, and chlorophyll-a were the primary determinants of dissolved oxygen variability. The findings provide detailed baseline data for ecological management of Oguta Lake. Keywords: dissolved oxygen, Oguta Lake, diel variation, stratification, Imo State.