Effects of Oxygenation Resuspension on DOM Composition and Its Role in Reducing Dissolved Manganese in Drinking Water Reservoirs

Anaerobic conditions in source water sediments are a key driver of manganese (Mn) release in drinking water systems. Enhancing sediment oxidation can inhibit Mn release, but the mechanisms of Mn speciation under varying oxidative conditions remain unclear. This study examined sediment exposure to oxygenated water layers at controlled dissolved oxygen levels (0, 2, 5, 7 mg L^-1) through laboratory simulations. Results showed Mn release is negatively correlated with DO (<i>R</i>² = 0.93, <i>p</i> = 0.034), with oxygen driving reactions between dissolved organic matter (C2 and C3 components) and forming functional groups (-OH, -COOH) that remove Mn through adsorption or complexation (C2: <i>R</i>² = 0.57, <i>p</i> < 0.001; C3: <i>R</i>² = 0.53, <i>p</i> < 0.001). Field studies in six reservoirs identified operational thresholds for sediment resuspension to mitigate Mn risks (compensation threshold: 17.4 μg L^-1; risk threshold: China: 95.5 μg L^-1; WHO: 70.8 μg L^-1). These findings clarify Mn-organic matter interactions and can provide practical guidance for Mn and algae removal in source water systems.