Ponds and lakes experience a phenomenon known as stratification where different layers of water are created due to differences in water density. The density of water is temperature dependent. It is at its greatest density at 4°C/39.2°F and becomes less dense at both higher and lower temperatures.
Late Summer – Early Fall
During the warmer months of the year, warm, oxygen rich water is trapped above cooler, nutrient rich, low oxygen water. The thermocline prevents the transfer of oxygen from the upper layer to the lower layer. Over time, the bottom layer of water loses more and more dissolved oxygen and can become uninhabitable for game fish. This oxygen poor environment also slows the breakdown of organic matter that accumulates on the bottom, leading to the build up of vast quantities of bottom sludge, which is high in nutrients.
Turnover : Spring and Fall
Stratified water bodies are also susceptible to turnover in the Spring and Fall when water temperatures in the top and bottom layers equalize. This allows the low oxygen bottom layer to mix with the upper layer, bringing up large quantities of nutrients and causing the dissolved oxygen concentrations to plummet. In some situations this can lead to fish kills.
Aeration is a solution for this type of phenomenon. It continually keeps the water from becoming stagnant and stratified, and keeps oxygen levels high throughout the body of water.
