THERMAL STRATIFICATION IN SHALLOW AQUACULTURE PONDS: RESPONSE TO TURBIDITY AND AERATION  

Water temperature directly affects the growth rate of all cultured aquatic species. Shallow water aquaculture ponds typically stratify thermally in the day and destratify at night. Thermal gradients are caused by the attenuation of solar radiation in the water, and attenuation is a function of water turbidity. The objectives of this study were to monitor temperature profiles in shallow aquaculture ponds as related to phytoplankton abundance, clay turbidity, and mechanical aeration.

The experiment was performed at the Auburn University E. W. Shell Fisheries Center Auburn, AL. Three, 0.04-ha research earthen ponds located side by side and with the same dimensions were selected. Each pond was supplied with a 0.37-kW Air-O-Lator aerator. In each pond, light intensity and water temperature at the surface, and at 20-cm depth intervals within the water column were monitored at 0.5-h intervals with a Model 64K HOBO Pendant^® Temperature/Light Data Logger. Air temperature under shade and in full sunlight also were monitored at 0.5-h intervals. Chlorophyll a concentration was measured weekly, while water turbidity and Secchi disk visibility were measured daily. The study was conducted in two phases. During the first phase, all aerators were alternatively turned on for 15 days (ON) and turned off for other 15 days (OFF). During the second phase, one pond had clear water, while the second one was treated with fertilizer to maintain phytoplankton turbidity. Kaolin clay added to a third pond to develop turbidity. Results showed that turbid ponds thermally stratified more strongly than did the clear pond. The cooling effect of aeration also was greater in turbid ponds than that in clear pond (Figure 1).