Another effect of lake turnover is known as “stratification.” Stratification occurs when the different layers of water in the lake do not mix completely. This can happen if the water at the bottom of the lake is much colder than the water at the surface.
Why do shallow lakes never stratify?
Shallow ponds and lakes may never stratify and turnover because winds keep the waters circulating throughout the year. Deeper lakes will appear clear during late summer, early fall, and early spring. As water temperatures change and turnover occurs, the waterbody will appear murky or dirty.
Why does stratification occur in winter?
During the winter months, stratification similar to that of the summer months will occur, but not to as great an extent. Because of the smaller temperature difference in the water column when spring approaches, the melting of the ice layer, winds, and storms are able to create spring turnover with little difficulty.
What is lake turnover?
Simply put, lake turnover is the seasonal mixing of the entire water column. For many lakes deeper than about 20 feet, distinct, thermally stratified layers of water form during the summer. These layers prevent the lake from mixing and aerating.
How and when does lake turnover happen?
This causes the temperature of the top and bottom layers of the lake to equalize. With the help of strong winds, this new equilibrium breaks the thermal stratification, and the lake is able to mix. Oxygen from the surface mixes with the bottom, while nutrients trapped near the bottom are free to mix throughout the lake. This is why, sometimes, in the spring and fall the lake can smell unpleasant. Decomposing organic materials are churned up from the bottom of the lake, bringing a signature sign of lake turnover.
What does this mean for oxygen levels and lake health?
Oxygen is most commonly depleted at the bottom of the lake by oxygen-hungry bacteria. These bacteria consume dead algae that sinks to lake floor.
What does it mean when a lake sinks to the bottom?
Meaning, water from the bottom of the lake rises to the top, and water from the top of the lake sinks to the bottom. The process allows for oxygen to be replenished and nutrients to be distributed throughout the lake. Did you know that deep lakes like Mendota and Monona are “dimictic,” meaning they undergo turnover twice during the year? ...
Why does water mix with the bottom of a lake?
Warmer and less dense water floats on the top of cooler, denser water at the bottom. Temperature layering begins to weaken when outside temperatures cool. This allows the lake to mix when temperatures equalize throughout the water column. Meaning, water from the bottom of the lake rises to the top, and water from the top of the lake sinks to the bottom. The process allows for oxygen to be replenished and nutrients to be distributed throughout the lake.
What is seasonal lake mixing?
Seasonal lake mixing. Twice a year, unseen forces churn water from the depths of our deeper lakes and deliver oxygen and nutrients essential to aquatic life. This temperature-driven process of lake “turnover” allows aquatic life to inhabit the entirety of the lake as oxygen becomes more available.
Why does a lake smell?
This is why, sometimes, in the spring and fall the lake can smell unpleasant. Decomposing organic materials are churned up from the bottom of the lake, bringing a signature sign of lake turnover.
What is stratification in lakes?
Lake stratification is the tendency of lakes to form separate and distinct thermal layers during warm weather. Typically stratified lakes show three distinct layers, the Epilimnion comprising the top warm layer, the thermocline (or Metalimnion ): the middle layer, which may change depth throughout the day, and the colder Hypolimnion extending ...
What are the three sections of lake stratification?
Lakes are stratified into three separate sections: I. The Epilimnion. II. The Metalimnion. III. The Hypolimnion. The scales are used to associate each section of the stratification to their corresponding depths and temperatures.
What is thermal stratification?
The thermal stratification of lakes refers to a change in the temperature at different depths in the lake, and is due to the change in water's density with temperature. Cold water is denser than warm water and the epilimnion generally consists of water that is not as dense as the water in the hypolimnion.
How does human land use affect lake stratification?
There are a number of ways in which human land use change influences lake stratification and subsequently water conditions. Urban expansion has led to the construction of roads and houses in close proximity to previously isolated lakes, a factor that has ultimately resulted in increased runoff and pollution.
How does human influence affect lake morphometry?
However, human influences in the form of land use change, warming temperatures, and changes to weather patterns have been shown to alter the timing and intensity of stratification in lakes around the globe.
How does thermal stratification affect water quality?
With severe thermal stratification in a lake, the quality of drinking water also can be adversely affected. For fisheries managers, the spatial distribution of fish within a lake is often adversely affected by thermal stratification and in some cases may indirectly cause large die-offs of recreationally important fish.
How does aeration affect lakes?
Many types of aeration equipment have been used to thermally de-stratify lakes, particularly lakes subject to low oxygen or undesirable algal blooms. In fact, natural resource and environmental managers are often challenged by problems caused by lake and pond thermal stratification. Fish die-offs have been directly associated with thermal gradients, stagnation, and ice cover. Excessive growth of plankton may limit the recreational use of lakes and the commercial use of lake water. With severe thermal stratification in a lake, the quality of drinking water also can be adversely affected. For fisheries managers, the spatial distribution of fish within a lake is often adversely affected by thermal stratification and in some cases may indirectly cause large die-offs of recreationally important fish. One commonly used tool to reduce the severity of these lake management problems is to eliminate or lessen thermal stratification through aeration. Aeration has met with some success, although it has rarely proved to be a panacea.
What is lake turnover?
Lake turnover is a natural phenomenon that can occur in any given lake during rapid changes in weather temperatures. A turnover is the rapid mixing of lake water. Turnover can have devastating effects on fish, plants, and amphibians that live in the lake.
How to prevent lake turnover?
Lake turnovers cannot be prevented as they are a natural occurrence, but proper aeration systems can help mitigate the harsh effects of a turnover. The main danger of a turnover is the overall diffused oxygen levels falling when the water is mixed. Maintaining a consistent mix of water all year long helps maintain healthy levels of dissolved oxygen levels. A sub surface aeration system will help keep the lake evenly oxygenated and consistent temperatures. 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 floating fountain can also increase circulation, which increases oxygenation and gas release, but is only recommended for lakes less than 15 feet deep.
Why is it important to prevent lake turnover?
Healthy lakes maintain that balance of consistent temperatures and oxygen levels throughout the water. Sub surface aeration systems are the most helpful resource in maintaining healthy water consistency and quality as you prevent lake turnover.
How deep should a lake be for a diffuser?
A floating fountain can also increase circulation, which increases oxygenation and gas release, but is only recommended for lakes less than 15 feet deep.
Why does water mix in a pond?
Once the top and bottom layers are the same temperature (and therefore density), wind and rain and cause the water to mix easily. During summer, in a poorly circulated lake, only the surface water is aerated and warmed by the sun. The water at the bottom of the pond is the coldest, densest, and contains the least amount of oxygen.
What is stratification in lakes?
Lake stratification is the tendency of lakes to form separate and distinct thermal layers during warm weather. Typically stratified lakes show three distinct layers, the Epilimnion (I) comprising the top warm layer, the thermocline (or Metalimnion): the middle layer (II), which may change depth throughout the day, and the colder Hypolimnion (III) extending to the floor of the lake.
Why is lake turnover important?
Lake turnover is extremely important in freshwater lakes as it is responsible for replenishing dissolved oxygen levels throughout the lake. When the lake is stratified in the summer months, the colder deep water (the Hypolimnion) is very low in oxygen. Once turnover occurs and the lake Is uniform in temperature and density, it takes very little wind energy to circulate the water. Wind moves the surface water, which is highly oxygenated, to the lake bottom, forcing low oxygen water from the lake bottom up to the surface, where it becomes saturated with oxygen.
What happens when water reaches 50 degrees Fahrenheit?
When surface water reaches about 50 degrees Fahrenheit in the fall, it becomes as dense as deeper water and sinks. The downward movement of surface water forces deeper water upward. The water begins to circulate, and this is called fall turnover.
What is the process of stratification of a lake?
When it comes to lake stratification, there are three different categories or layers. When the surface of a lake is warmed by the sun, water density begins to change, and thus the process of stratification begins. WInd then plays a significant part in mixing the upper layer of water, creating motion for the warm water and cool water to shift. Water that is cooler is denser, and so it circulates to the bottom of the lake, while the warmer water remains closer to the surface.
What are the factors that determine the classification of a lake?
From thermal classification to stratification, and the lake zone categories, all of these systems of categorizing lakes rely on the influence of external factors such as the sun, the lake’s density and composition, and the climate in which the lake sits . The continued study of lakes and the systematic classification of those lakes allows for clearer scientific research into everything from climate change to habitat conservation, weather patterns and aquatic compositions. This research furthers human’s understanding of a variety of topics, not just the specific lake being studied.
What is the profundal zone of a lake?
The profundal zone is the section that follows the Limnetic once the sunlight cannot penetrate the lake’s surface any further. The temperature in these waters is also significantly colder, as the warmth from the sun is unable to reach these depths. The water clarity and composition has a significant effect on how deep the sunlight is able to reach, and therefore the size and depth of the profundal layer will vary from lake to lake. There is also a decreased amount of oxygen in this region of the lake, so the amount of fish in this area are also significantly less.
What is the season of dimictic lakes?
Dimictic lakes experience seasons. This means they have both a winter stratification below ice and a summer stratification. Circulation only occurs in these lakes during the fall and spring months.
What is the term used to describe the way lakes separate into layers based on temperature?
Lake stratification is the term used to describe the way lakes separate into layers based on temperature. Though related to the lake zones, this classification is strictly thermal. The change in temperature is due in part to the amount of light which can penetrate that lake’s waters. Because of this, lake density plays a key role in the temperature of the layers, and stratification more generally.
What is the limnetic zone?
The next layer is called the limnetic zone and is the surface or open water section of the lake. The limnetic zone is classified by the amount of light that penetrates the body of water. This upper water layer is also referred to as the euphotic zone, and is the part of the lake that is warmest and receives the most sunlight. Once the sunlight can no longer penetrate the lake, the zone ends. Like the Littoral zone, aquatic plants thrive in this region, due to the presence of sunlight. Oxygen levels are also higher in this section of the lake, meaning the majority of fish also live in this zone.
How does wind affect stratification?
Stratification is affected by the size, shape and depth of the lake. Larger and deeper lakes tend to have greater stratification. With small or shallow lakes, wind can affect much more of the water within the lake, thereby causing the entire lake to mix and move with the wind currents.
Why do lakes have a turnover?
The turnover in a lake happens in the Fall and the Spring and is caused by the seasonal changes that come with them.
When does thermal stratification occur in lakes?
Because of the wide range of temperatures in lake water, Thermal Stratification is a typical natural occurrence. that happens in late Spring and Summer. The lake will have 3 different layers of temperature. The sun warms the uppermost layer and cooler water separates into 2 more layers.
Why is spring turnover important?
Once thermal stratification sets up, the deeper Hypolimnion level does not get mixed to the surface and whatever dissolved oxygen exists in the Epilimnion level of the lake is all that is available until lake turnover in the fall.
What contributes to the low dissolved oxygen content in a lake?
The decomposing organic matter at the lake bottom contributes to the low dissolved oxygen content. The coolest water at this level is the densest and weighs the most while the warmer water in the Epilimnion is less dense. The deeper the lake the larger the gradients become in the Thermal Stratification.
What happens when the lake turns over?
When the Fall Turnover happens, prevailing winds over the surface start to get colder and slowly cool down the top layer which makes the surface water with the help of these cold winds, heavier and causes them to sink. This will cause the cause Turnover and makes the whole lake mix the water column of the entire lake called the Fall Turnover. Water at lower temperatures and denser can mix much easier.
Which layer of the lake is characterized by a steep gradient in temperature?
Metalimnion level – is the middle level that is characterized by a steep gradient in temperature and is the barrier that prevents mixture and the heat exchange between the Epilimnion level and the Hypolimnion levels in the lake. This layer is also called the Thermocline because of its rapid decrease in temperature and O2 concentration levels.
How long does a spring turnover last?
It may last several weeks if the weather is cool and windy, or a matter of days if the weather suddenly turns hot and calm.
Overview
Lake stratification is the tendency of lakes to form separate and distinct thermal layers during warm weather. Typically stratified lakes show three distinct layers, the Epilimnion comprising the top warm layer, the thermocline (or Metalimnion): the middle layer, which may change depth throughout the day, and the colder Hypolimnion extending to the floor of the lake.
Definition
The thermal stratification of lakes refers to a change in the temperature at different depths in the lake, and is due to the density of water varying with temperature. Cold water is denser than warm water and the epilimnion generally consists of water that is not as dense as the water in the hypolimnion. However, the temperature of maximum density for freshwater is 4 °C. In temperate regions where lake water warms up and cools through the seasons, a cyclical pattern of overtur…
De-stratification
In temperate latitudes, many lakes that become stratified during the summer months de-stratify during cooler windier weather with surface mixing by wind being a significant driver in this process. This is often referred to as "autumn turn-over". The mixing of the hypolimnium into the mixed water body of the lake recirculates nutrients, particularly phosphorus compounds, trapped in the hypolimnion during the warm weather. It also poses a risk of oxygen sag as a long establi…
Anthropogenic influences
Every lake has a set mixing regime that is influenced by lake morphometry and environmental conditions. However, changes to human influences in the form of land use change, increases in temperatures, and changes to weather patterns have been shown to alter the timing and intensity of stratification in lakes around the globe. These changes can further alter the fish, zooplankton, and phytoplankton community composition, in addition to creating gradients that alter the availa…
See also
• Aquatic Science
• Stratification (water)
• Hypoxia
• Freshwater ecosystems
• Water column