How and Why Lakes Stratify and Turn Over: We explain the science behind the phenomena
- Spring to Summer: Lakes begin to stratify due to differences in temperature Thermal stratification occurs when the water in a lake forms distinct layers through heating from the sun. ...
- Summer to Fall, and Winter to Spring: The lakes turn over ...
- Around the World: Different lakes, different stratification and different turnovers ...
What causes stratification in water?
Stratification occurs as a result of a density differential between two water layers and can arise as a result of the differences in salinity, temperature, or a combination of both. Stratification is more likely when the mixing forces of wind and wave action are minimal and this occurs more often in the summer months.
Why does lake thermal stratification occur?
Such thermal stratification occurs because of the large differences in density (weight) between warm and cold waters. Density depends on temperature: water is most dense (heaviest) at about 39EF, and less dense (lighter) at temperatures warmer and colder than 39EF.
How and why lakes stratify and turn over?
How and when does lake turnover happen? Due to seasonal changes in sunlight intensity, surface water temperature begins to transition in the spring and fall. In the spring, the water surface warms. This causes the temperature of the top and bottom layers of the lake to equalize.
What does stratification mean in lakes?
Stratification is defined as the development of relatively stable light and warm layers above colder deeper layers within a body of water. Thermal stratification is related to water density and is effected by incoming heat, water depth, and the degree of water-column mixing.
How deep should a lake be to stratify?
If a lake is deep enough, typically a mean depth of 8 to 10 feet or greater, it can thermally stratify, which means the surface waters are a lot warmer than the deep waters.
How do lakes stratify with depth?
In lakes and ponds with sufficient depth, when surface waters warm and become more buoyant in the spring and over the course of the summer, vertical differences in water temperature can cause the water column to stratify, or separate into distinct layers (Fig.
What temperature do lakes turnover?
Water is at its heaviest at 39 degrees, so as the surface temperatures drops to around 50 degrees, that top layer of water becomes heavier and wants to sink. Lakes can take a few days to turn or it can happen over night. A cold front, cold rain, or a heavy wind can increase the turnover rate.
How do you tell if a lake has turned over?
When a lake turns over, what is happening is that the cooler water on the bottom of the lake will mix with the warmer water at the top of the lake for a brief time period. In most cases you will periodically see small bubbles coming from the bottom all the way to the surface.
What causes a lake to turnover?
When the temperatures drop, the top layer of water starts to get colder as well. It inevitably reaches a point in which it becomes denser than the water underneath, therefore causing it to sink. During this process, the bottom layer of water starts shifting to the top – hence the term turning over.
How do you control stratification?
The key to controlling stratification is to find a way to get the heated air at the upper levels of the space to drop down and mix with the cooler air at lower levels. There are two major ways to do this: axial fans and high-volume, low-speed fans.
Is Lake stratification good or bad?
Lake stratification is natural and necessary to lake health, though lack of DO at deeper depths can pose problems. Using nanobubbles to add DO back in the water and maintain thermal stratification is the best way to promote healthy lakes.
How stratification affects water quality?
Stratification of the lake's waters prevents more oxygen from reaching the bottom water. Even so, the oxygen supply in the Eastern Basin does not get used up dur- ing the summer, because the supply was very high at the begin- ning of the summer.
How thermal stratification affect the composition or quality of water in lake?
Thermal stratification occurs at a majority of deep reservoirs resulting from the surface warming. It stops mixing and prevents reaching oxygen to the bottom depths. These result water quality detritions in the bottom layers.
How stratification affects water quality?
Stratification of the lake's waters prevents more oxygen from reaching the bottom water. Even so, the oxygen supply in the Eastern Basin does not get used up dur- ing the summer, because the supply was very high at the begin- ning of the summer.
What causes lake turnover?
What causes lake turnover? Turnover is like a dog learning to roll over. Fall and spring turnover are natural phenomenon that cause the top layer of the lake (the epilimnion) and the bottom layer of the lake (the hypolimnion) to trade places. In the fall, this phenomenon happens when the temperature in the air drops.
What happens in lakes when eutrophication occurs?
Eutrophication is the process in which lakes receive nutrients (phosphorus and nitrogen) and sediment from the surrounding watershed and become more fertile and shallow. The additional nutrients are food for algae and fish, so the more eutrophic a lake is, the more living organisms it sustains.
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 stratify?
Spring to Summer: Lakes begin to stratify due to differences in temperature. Thermal stratification occurs when the water in a lake forms distinct layers through heating from the sun. When the ice has melted in the spring, solar radiation warms the water at the surface of the lake much faster than in deeper waters.
How many layers of stratification are there in a lake?
When a lake stratifies, three different layers typically form.
What causes the water in the epilimnion to mix deeper and deeper?
Throughout the summer, wind and waves cause the warming water in the epilimnion to mix deeper and deeper, slowly incorporating hypolimnetic water through the metalimnion. The ability of a lake to mix through wind turbulence is determined by the “stability” of thermal stratification.
Why is dissolved oxygen important for all aquatic organisms in a lake?
Though dissolved oxygen doesn’t play a direct role in lake stratification and turnover , it is important for all the aquatic organisms in a lake that require oxygen to survive. The deepest layer is the cold, dense water at the lake bottom, called the hypolimnion.
What are the different types of lakes?
Six common lake types are: 1 Amictic: covered in ice all year. This mixing pattern is typical of lakes in the Antarctic. 2 Cold monomictic: water never gets warmer than 4°C and turnover occurs once in summer. Lakes in the Arctic are often cold monomictic. 3 Dimictic: like at IISD-ELA, lakes are stratified in summer and winter, and mix once in spring and once in fall. 4 Warm monomictic: water cools to near 4°C in winter, when turnover may occur. Lakes are stratified during other times of the year and are not ice covered. Lakes in the tropics or low altitudes in northern temperate areas can be warm monomictic. 5 Oligomictic: water generally warm and stratified, occasionally cools to generate circulation at irregular intervals. This mixing type can occur in lower latitude regions where there is little variation in annual temperature. 6 Polymictic: frequent mixing throughout the year. This type of mixing can occur in lakes across the world and depends on characteristics like depth, size, and shape of a lake.
What to do when you are next swimming in a freshwater lake?
When you are next swimming in a freshwater lake, impress all your friends by dipping your toes from the epilimnion, through the metalimnion and into the depths of the hypolimnion!
Why is lake turnover important?
Lake turnover is extremely important in freshwater lakes, as it is the event that is responsible for replenishing dissolved oxygen levels in the deepest lake waters. When the lakes are a uniform temperature and density, it takes relatively little wind energy to mix water deep into the lake.
concentration of oxygen
In the warmer seasons, although surface waters may remain more or less saturated and even supersaturated, the concentrations are lower. Beneath the surface, oxygen consumption through biological decay may cause serious depletion. Oxygen depletion also occurs near the bottom because of processes at the mud-water interface, many of which are…
heat transfer
When a lake is stratified, the most important process for downward transfer of heat to the hypolimnion is through eddy conduction. The coefficient of eddy conductivity is determined empirically and varies substantially from lake to lake. Mixing processes are generally more active in coastal areas, so that…
