Description

Abstract: Density stratification isolates near-surface from bottom pond waters and prevents exchange of dissolved oxygen (DO) and nutrient elements, potentially restricting photosynthesis and production. Destratification strategies have become important for cost-effective intensification of pond aquaculture. Evaluation of methods and devices has emphasized effects on production, with little detailed description of effects on physico-chemical components of pond ecosystems. This paper describes short-term effects of mechanical mixing on temporal and spatial distribution of temperature and DO in tropical freshwater fish ponds. Intensely stratified ponds of 1.5 m depth were monitored at eight depths for temperature and two depths for DO every 30 min with a modest-cost automated system of commercially available hardware. Results are presented as time-series plots, isotherm diagrams of temperature distribution with time and depth, and a stability index of energy required to mix a pond to uniform temperature. Required mixing energy is minuscule compares with electrical energy consumption of the lowest powered mixing devices discussed in literature. Strategy for application of mechanical energy to water is critical for efficiency. A relatively subtle difference between two mixing regimes (daytime mixing for one 2-h period or two 1-h periods) produced potentially important differences in temperature and DO distribution.