Follow the below steps for the greatest chance of stopping stratification in your dam, lake or (deep) pond
What is stratification in water bodies?
Stratification refers to layers forming in a water body at different depths in the absence of mixing. The layers are divided based on density—the denser colder water remains below the lighter warmer water.
Beyond temperature, stratification also affects the exchange of oxygen and nutrients in a water body. For instance, cold bottom layers will be more likely to have more nutrients and less oxygen than the warmer layer that sits above it.
Stratified lakes, dams and deep ponds often display three distinct layers: (i) the epilimnion, which is the top, warm layer, (ii) the thermocline, which is the middle layer and often changes depth during the course of the day, and (iii) the hypolimnion layer, which is the coldest layer extending to the floor of the water body.
How does stratification occur?
Stratification can occur in deep water bodies when there is inadequate mixing of water through the water column. A water body that doesn’t see much wind action and waves on the surface, at least from time to time, is susceptible to stratification. Without adequate mixing, layers begin to form as colder, denser water heads down and warmer, lighter water heads up.
Over time, the layers can become more distinctly separated as each system applies more pressure on the other, e.g. as the pressure builds, the cold water pushes away the warm water more which itself increases the pressure. So, the colder layer only gets colder and the warmer layer only gets warmer.
What is the problem with stratification?
The biggest problem that can occur from stratification is a turnover event. This is when a large force on the water, like severe winds, rain or a large discharge from a river, breaks the layers and triggers them to mix all at once. This is when mass fish kills typically happen. The fish are all living at the surface where it's warm and there is plenty of oxygen, then a turnover event occurs, and all that warm water and oxygen is diluted to such a point, the fish can no longer breathe and they all die.
How to reduce stratification
Mixing the water in your entire water column is the key to removing stratification. In the absence of a lot of wind action–how Mother Nature does it–, your best method is aeration. For deep water bodies, more than 5m, look at sub-surface aerators. If your water is less than 5m, you could choose a surface or sub-surface aerator.
Sub-surface aerators
Sub-surface aerators have one on-land motor pumping air out to air-stations that are sitting on the floor of your water body. These air-stations release bubbles that rise up, getting larger and larger as they go. These bubbles break open layers that may already exist in the water body and ensure no layering can form going forward.
Surface aerators
Surface aerators mimic Mother Nature’s wind action. The moving water agitates the surface of the water creating ripple (or wave) action that naturally mixes the water. A benefit of surface aerators is they add oxygen to water faster than sub-surface aerators, making them ideal in emergency situations, e.g. trying to get oxygen to dying fish asap.
surface
Surface aeration
Surface aerators sit on the surface of the water and use a propeller to pump water up into the air. This allows for gas exchange between the water and the air where oxygen enters the water before it returns to the waterbody. Agitating the surface of the water also creates a ripple effect which increases the surface area of the waterbody. More surface area means more gas exchange, resulting in greater aeration.
sub-surface
Sub-Surface aeration
Sub-surface aerators involve using air-stations (often multiple) set up on the floor of your dam. These systems pump out air which becomes bubbles. These bubbles rise to the surface, getting larger and larger as they climb. This drags less-oxygenated bottom-waters to the surface where oxygen can enter the water. The constant "bottom up" circulation provided by the rising bubbles moves more highly oxygenated water to the bottom where it's needed most.
3-Month Trial: Aeration Stops Stratification in 6 Acre Lake
