This is why the discharge for dams in the winter is warmer than the lake’s surface. The deeper we go the water temperatures will warm to as much as 39 degrees at the reservoir’s bottom. Working down through the ice, we will ultimately find liquid water, which at the ice’s edge will be approximately 32 degrees. At this point the lake will have a coat of ice that will be colder than 32 degrees Fahrenheit at the lake surface. Let’s start with a Colorado lake that is moderately deep, say 50 feet, just prior to spring thaw. Turnover is best understood by walking through the four seasons and looking at the water processes that are occurring. Consequently, in the spring and the fall around ice-off and ice-up there is a short period when the water temperature of a lake is 39 degrees throughout, allowing for water to mix or turnover if you will. Without this property, large bodies of water would be frozen solid anywhere it gets cold enough to freeze, as frozen water would sink to the bottom until only a skim of liquid water existed on the surface. Which means ice is less dense allowing it to float on its liquid counterpart. In order to understand turnover, one needs to understand that water is densest at approximately 39 degrees Fahrenheit. There’s little doubt in my mind that many use the term “turnover” to describe any change in water conditions, especially if those conditions are visual, smelly and/or associated with a fish kill, all symptoms of events other than turnover. I’m fairly sure most of these “turnover” reports are actually algae blooms. Often these are made during the summer or early fall. Sub surface aeration systems are the most helpful resource in maintaining healthy water consistency and quality as you prevent lake turnover.Every year I see several conditions report stating the lake is turning over. Healthy lakes maintain that balance of consistent temperatures and oxygen levels throughout the water. Mitigating the harmful effects of lake turnovers is important for the health of fish and plants in the lake. A floating fountain can also increase circulation, which increases oxygenation and gas release, but is only recommended for lakes less than 15 feet deep. A diffuser will release bubbles from the bottom of the lake, and as the bubbles float upwards, they will mix the water and help gases release. A sub surface aeration system will help keep the lake evenly oxygenated and consistent temperatures. Maintaining a consistent mix of water all year long helps maintain healthy levels of dissolved oxygen levels. The main danger of a turnover is the overall diffused oxygen levels falling when the water is mixed. Lake turnovers cannot be prevented as they are a natural occurrence, but proper aeration systems can help mitigate the harsh effects of a turnover. As the ice melts, the surface temperature will rise and eventually equal the warmer water at the bottom of the lake, which has been slowly depleting of oxygen and accumulating harmful gases. Ice is less dense than water ice floats to the top of the lake. During the wintertime, the warmest water is at the bottom, which is where all of the pond life will live during the winter. Spring turnovers occur as the weather warms up after winter, and the top layer warms up again. This is when a fish kill could occur due to poor oxygen levels. If there is more oxygen depleted than oxygenated water, the overall levels of oxygen in the lake can fall during the turnover. The seasons change and slowly the water at the surface cools down and eventually is the same temperature as the cold water at the bottom. The water at the bottom of the pond is the coldest, densest, and contains the least amount of oxygen. Once the top and bottom layers are the same temperature (and therefore density), wind and rain and cause the water to mix easily.ĭuring summer, in a poorly circulated lake, only the surface water is aerated and warmed by the sun. There are typically three layers, the epilimnion (top), thermocline (middle), and hypolimnion (bottom). The cold water sinks to the bottom while the warm water floats to the top. How Does a Turnover HappenĬold water water is more dense than warm water bodies of water like lakes become layered based on temperature. Learn how turnovers can happen and how to prevent their devastating effects. Anytime a turnover occurs, dissolved oxygen levels can be at stake. Turnover can have devastating effects on fish, plants, and amphibians that live in the lake. A turnover is the rapid mixing of lake water. Lake turnover is a natural phenomenon that can occur in any given lake during rapid changes in weather temperatures.
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