Water stratification describes how a water body separates into layers with different temperatures. You might hear this called thermal stratification which is common in dams and shallow lakes. But if your dam or lake isn’t managed well, water stratification can cause certain issues.
What Is Water Stratification?
The term ‘water stratification’ is given to water in a dam or shallow lake that separates into distinct thermal layers. This commonly happens during warm weather as the water near the surface gets hotter than the deeper water. Each layer of water has a varied temperature and a density difference.
Stratification can also occur in ocean basins with the surface ocean attracting more warmth. But there is generally more movement in the ocean than in lakes and dams, which can sometimes become stagnant.
Here are the three layers of water that are present in water stratification:
Bottom Layer
The bottom layer of the water is called the Hypolimnion. It is found at the deepest part of the dam or lake and is often the coldest. This is because the sunlight can’t reach the bottom layer of cold water. The level of oxygen present in the bottom layer of water is also low.
Middle Layer
The middle layer of water is known as the Metalimnion. This middle layer is a barrier between the cold, bottom layer of water, and the top, warm water layer. So, the temperature in the middle layer is warmer than the bottom layer but colder than the top layer.
Top Layer
The upper layer of water is called the Epilimnion and is the surface layer of the dam or lake. This water is less dense and is much warmer as it’s closer to the sun so it is a warm layer. Dissolved oxygen is common in the Epilimnion layer.
How Does Thermal Stratification Occur?
Water stratification occurs when there’s a lack of aeration in the dam water. This is typical in stagnant water where the water has not moved for a long time. Limited circulation and aeration prevent oxygen from travelling through the water body, resulting in water stratification.
This is more common in deep dams and lakes as there’s a bigger temperature difference between the top and bottom layers. The heat from the sun warms up the top water layer but doesn’t reach the bottom sections of the dam.
What’s the Impact of Water Stratification?
Several problems can arise due to water stratification. The main reason for the issues that occur is due to the lack of oxygen in the water at the bottom layer.
Let’s take a look at the impact of dam and lake stratification:
Low Oxygen Levels
The bottom layer of the dam will have a low oxygen level when water stratification has occurred. This is harmful to fish and aquatic life which need oxygen to survive. Poor oxygen levels can also result in bad odours and cloudy water.
Algae Growth
Water stratification encourages algae to grow in the water where it is warm. More algae growing in the water lowers the quality of water and can make your dam unpleasant to swim in.
Nutrients Trapped
Water stratification causes nutrients to get trapped in the bottom layer of the dam. The fish and aquatic plants in the top layer of the dam have fewer nutrients available to them.
How Can I Prevent Water Stratification?
Aeration Solutions
The best way to prevent stratification in your dam water is to install an aeration solution. An aeration system mixes and circulates the water so it doesn’t become stagnant. It also adds oxygen to the water by pumping water or air into the waterbody.
You can opt to install a surface aerator or a sub-surface aerator. A surface aerator adds air to circulate the water at the surface. The top layer of water becomes oxygenated and cooler, and encourages circulation with bottom waters.
A sub-surface aerator, or bottom diffuser, injects air from the bottom of the dam. Air is released so the bubbles rise to the top layer of dam water and the water circulates. These bubbles break open the stratified layers. The bottom layer bubbles are also cooler so they lower the temperature of the top water layer.