Modification of Streeter-Phelps Model for Dissolved Oxygen Concentration in a River: Incorporating Extended Sources and Sinks

Abstract Dissolved Oxygen (DO) is a critical parameter reflecting the health and sustainability of aquatic ecosystems. The classical Streeter–Phelps model accounts primarily for oxygen dynamics governed by atmospheric reaeration and carbonaceous biochemical oxygen demand (CBOD). However, actual river systems experience more complex interactions involving additional oxygen sources and sinks, including nitrogenous biochemical oxygen demand (NBOD), sediment oxygen demand (SOD), photosynthetic oxygen production, and ecosystem respiration. This study extends and modifies the Streeter–Phelps model to account for these omitted processes. The modified model presents a comprehensive approach by deriving deficit expressions for each contributing factor, using standard techniques such as integrating factors and boundary condition application. A case study was conducted using Mamu River in Anambra State of Nigeria, with field measurements collected and used to calibrate the model. The result is a combined equation for total DO deficit that better reflects the physical, chemical, and biological interactions in natural water systems, validating its superiority over the classical model.