Effects of fish bioturbation on the vertical distribution of water temperature and dissolved oxygen in a fish culture-integrated waste stabilization pond system in Vietnam

The integration of wastewater stabilization with fish culture in a single-pond system is a double-benefit both due to the reclamation of the wastewater and fish production. In conventional fish ponds, it is known that fish activities (bioturbation) result in ecological benefits as they stir the sediment layer, improving aerobic conditions and, enhancing the oxidation of detritus in this layer. However, the effects of the fish bioturbation in integrated wastewater stabilization fish production systems are little known, especially the enhancement of aerobic conditions in the lower layers of the water column where anaerobic conditions dominate, constraining oxidation of organic matter. The present study was designed to evaluate the effects of three factors (fish bioturbation, season and water depth), as well as their interaction, on the vertical distribution of two factors influencing wastewater treatment efficiency in stabilization ponds—water temperature and dissolved oxygen (DO). In contrast to the pond without fish, there was no significant difference in temperature between the water depth (20, 50 and 80 cm) in the pond with fish in the dry season ( P > 0.05). As indicated by DO monitoring in early morning and on a diel basis, in both dry and rainy seasons the DO saturation percentage of the surface layer of water (20 cm) was not different between the ponds with and without fish. However, with an increase in water depth, the DO saturation percentage of the pond with fish was significantly higher than that of the pond without fish ( P < 0.05). Quiescence of DO variation (invariable linear pattern) in the pond without fish at depths of 50 and 80 cm was recorded. Only fish production and water depth factors had significant effects ( P < 0.001), and the interaction between them was highly significant ( P < 0.01).