Understanding the photochemistry of coastal hypoxic blackwater

Deoxygenation is the major process behind generation of hypoxia and so-called blackwater in coastal waterways. This thesis investigated the potential for photochemical deoxygenation in the Richmond River system, northern NSW, through laboratory studies involving simulated solar irradiation of solutions containing standard dissolved humic substances and a field study on natural hypoxic blackwaters formed in the Richmond River system after a flood in 2017. Dissolved oxygen, optical properties, redox state of organic matter, pH and iron concentration were identified as key parameters. The results suggest photochemistry may significantly contribute to deoxygenation potential in shallow waters with high concentrations of organic matter.