Forecasting of dissolved oxygen in marine fish culture zone

Short-term trends in dissolved oxygen in a weakly flushed marine fish culture zone in Hong Kong are studied by a real-time water-quality model with seven system variables: dissolved oxygen, chlorophyll-a, organic nitrogen, ammonia, nitrate, zooplankton, and sediment algal carbon. The carbon-chlorophyll ratio is computed as a function of a time-variable saturating light intensity. Sediment oxygen demand is related to organic loads from the fish farm as well as algal biomass. Water-quality predictions are compared with well-documented field observations for both background and algal bloom conditions, over time scales on the order of a month. Model simulations demonstrate the importance of light intensity and photosynthetic production in dissolved oxygen variations, which are well predicted. The model also provides useful insights into the causes of severe oxygen depletion and phytoplankton dynamics in a eutrophic subtropical coastal marine ecosystem.