Surface Water Quality Modeling & Eutrophication Kinetics: Streeter-Phelps Dynamics, Nutrient Loading, and Algal Bloom Kinetics
Surface water quality modeling and eutrophication kinetics analyze the hydrodynamic transport, dissolved oxygen (DO) dynamics, and nutrient enrichment pathways in rivers, lakes, and reservoirs. Anthropogenic discharges containing excessive nitrogen and phosphorus trigger rapid algal biomass growth, leading to severe dissolved oxygen depletion, loss of aquatic biodiversity, and overall ecosystem degradation. The classical Streeter-Phelps Dissolved Oxygen Sag Model quantifies the balance between biochemical oxygen demand (BOD) deoxygenation and atmospheric reaeration along a river reach ($x = v \cdot t$): $$D(t) = \frac{k_1 \cdot L_0}{k_2 - k_1} \left( e^{-k_1 \cdot t} - e^{-k_2 \cdot t} \right) + D_0 \cdot e^{-k_2 \cdot t}$$ Where $D(t)$ is dissolved oxygen deficit ($D = \text{DO}_{\text{sat}} - \text{DO}$ at time $t$), $L_0$ is initial ultimate BOD concentration after point-source mixing, $D_0$ is initial DO deficit, $k_1$ is deoxygenation rate constant ($\text{day}^{-1}$), and...