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Diurnal stratification of oxygen in shallow aquaculture ponds in central Europe and recommendations for optimal aeration

Oberle, Martin, Salomon, Sebastian, Ehrmaier, Bruno, Richter, Peter, Lebert, Michael, Strauch, Sebastian M.
Aquaculture 2019 v.501 pp. 482-487
Cyprinus carpio, Internet, aeration, aquaculture, fish, hypoxia, livestock, mixing, oxygen, ponds, solar energy, solar radiation, surface water, temperature profiles, Central European region
The common carp (Cyprinus carpio) is an important livestock in regions of Central Europe, where it is bred in shallow, turbid ponds (mean depth 1 m). A frequent problem observed in this form of aquaculture is hypoxia, which confines the fish close to the surface, preventing them from optimally feeding at the bottom. According to information propagated in textbooks and good practice guidebooks and internet documents, the best solution to that is aeration in the early morning hours, when oxygen concentration is supposed to be minimal. While we wanted to test the feasibility of photovoltaic power for aeration of ponds, we detected that on days with bright sunshine the lowest oxygen concentration occurs in the afternoon at the bottom layer of a shallow pond, and that oxygen distribution is highly influenced by thermal stratification. This formation of layers of different temperatures within the water body inhibits the diffusion of oxygen. A breaking of the stratification effectively increases the oxygen concentration, elevating the overall amount of oxygen in the pond. Consequently, the drop in oxygen concentration at night is less dramatic, and critically low levels of oxygen in deeper zones of the pond are avoided. A comparison between the oxygen distribution and daytime or nighttime aeration showed that on days with bright sunshine it is more effective to force mixing of the entire water column during the day, making the use of a photovoltaic power system feasible. This offers a simple and elegant solution for ponds which are not connected to the power grid.