Seasonal and Tidal variations of DO, BOD, and Nutrients in Major Rivers within Eastern Niger Delta, Nigeria

River channels within the Oil producing Area of Nigeria are highly impacted by the activities of the Oil Companies. This work examined the Dissolved oxygen (DO), Biochemical oxygen demand (BOD), Nitrate (NO3-), Phosphate (PO43-), and sulphate (SO42-) in Calabar, Cross River, Imo, Great Kwa, and Qua-Iboe Rivers using standard procedures. Results showed that, DO, BOD, NO3-, and SO42- were within their limits by NESREA whereas, PO43- was higher than the limit. Mean levels of NO3-, PO43-, and SO42- were higher during the dry season and low tidal regime while DO and BOD showed higher levels in wet season and high tidal regime. Results also indicated that, DO belong to the slightly polluted class, BOD, NO3-, and SO42- belong to the non-polluted class whereas, PO43- varied between moderately polluted and the severely polluted classes in the studied aquatic channels. Generally, the relationships among the parameters varied from one parameter to the other. Principal component analysis (PCA) identified mainly the anthropogenic factor and moderately the natural factor as being responsible for the levels of the parameters assessed in the studied rivers. Hierarchical clusters analysis (HCA) recorded common associations and sources for the DO and BOD, PO43- and SO42- while NO3- had a separate and personal cluster. The study revealed the existing relationships among the studied parameters and their related impact on the health of the aquatic ecosystems investigated.