UBEJI AXIS

Estuarine ecosystems in industrial regions like the Niger Delta face increasing threats from pollution, habitat loss, and biological stress, highlighting the need for integrated environmental assessments. This study assessed the ecological and biological integrity of the Ubeji axis of the Warri River, Delta State by combining physicochemical and biological data with multivariate and environmental risk analyses. Sampling was from April to December 2024 and focused on water and sediment quality, heavy metal levels, and biological responses of five Macrobrachium species: M. macrobrachion, M. rosenbergii, M. vollenhovenii, M. equidens, and M. dux. Physicochemical parameters such as Water Temperature, pH, Electric Conductivity were measured in situ while heavy metals were tested for in the Laboratory using standard analytical methods. Canonical Correspondence Analysis (CCA) were used to examine species–environment relationships. Pollution levels and ecological risks were evaluated using Contamination Factor (CF), Geoaccumulation Index (Igeo), Enrichment Factor (EF), Pollution Load Index (PLI), and Potential Ecological Risk Index (PERI). The Distribution coefficient (Kd) was calculated to ascertain the bioavailability of the metals. Results revealed clear seasonal variability in surface water quality driven by rainfall and anthropogenic inputs. Dissolved oxygen (3.85–4.50 mg/L) remained below WHO, US EPA, and FMev thresholds, while pH, conductivity, and nutrients stayed within acceptable limits. Strong and species-dependent Pearson correlations demonstrated that sediment is the dominant exposure route for all Macrobrachium species. Iron (Fe) showed strong correlations in M. rosenbergii (r = 0.722, p < 0.05), M. vollenhovenii (r = 0.989, p < 0.001), and M. equidens (r = 0.661, p < 0.05), while M. macrobrachion showed a weak, non-significant association (r = 0.181, p > 0.05). Zinc (Zn) correlated significantly only in M. vollenhovenii (r = 0.917, p < 0.001); correlations in M. macrobrachion (r = 0.547, p > 0.05), M. rosenbergii (r = 0.131, p > 0.05), and M. equidens (r = 0.491, p > 0.05) were weak or non-significant. Canonical Correspondence Analysis (CCA) explained 79.88% of species–environment variation, identifying sediment texture and metal loading as the main ecological drivers. Distribution coefficients (Kd) showed strong sediment retention for chromium (55) and iron (66.89) in June, while cadmium remained predominantly mobile across months. Risk indices revealed ultra-high enrichment for cadmium (EF > 5), though the geo-accumulation index indicated sediments were unpolluted (Igeo < 0). The Pollution Load Index remained low (PLI = 0.103), and ecological risk assessment showed cadmium posed the highest but still low overall ecological risk (mean PERI = 45.67). In conclusion, the river maintains good ecological integrity with low metal contamination, but cadmium enrichment signals early anthropogenic influence. Although sediments are currently unpolluted, continuous monitoring is recommended to prevent future ecological impairment.