Modeling dissolved oxygen in a crab pond

In aquaculture, dissolved oxygen (DO) is vital to crab growth. Different from DO in flowing water area, the dynamics of DO in a crab pond is deeply affected by complex interactions between organism communities and meteorological factors. Significant fluctuations of DO content occurs within 24 h. It is thus important to explore DO dynamics related to various environmental factors for real time DO content prediction, water quality analysis, and artificial aeration control. In this work, a dynamic model based on the diffusion theory was developed to reflect daily variations of DO content at different depths in a crab pond. The model focuses on evaluating the effects of macrophyte and aerator on the production of DO, and the effects of extinction coefficient and diffusion coefficient on the vertical distribution of DO. Photosynthesis and respiration of aquatic macrophyte, mechanical aeration, mineralization, and meteorological conditions were considered. The model can fit experiment data with mean absolute percentage error about 6%. Simulation results show that the main process that produces DO in the pond is photosynthesis of macrophyte, which accounts for 88.2% of the DO source. Mechanical aeration adds 9.2% of DO while reaeration adds 2.6% of DO. The main process that consumes DO is mineralization which accounts for 86.9% DO sink, followed by respiration of macrophyte which utilizes 13.1% DO, the effect of crabs on DO content is small. DO at different depths was also simulated, and it can be found that hypoxia is more likely to occur in the bottom water where diffusion coefficient decreases. The established DO model serves as a launching point for further research on artificial aeration control to improving aquaculture water environment.