POND STRATIFICATION By: Josh Hehmeyer

In Ohio, ponds and lakes may go through a process called thermal stratification which means the body of water becomes layered with a substantial difference in the temperature of the top layer and the bottom layer.  There are many different factors in whether or not a body of water will stratify. 

During the early spring there is usually plenty of cool rain and cool weather to keep the water temperature consistent throughout the entire body of water.  There is also most likely enough wind to keep the body of water circulating.  How this works is, the wind blows the water across the surface and it piles up on the downwind side forcing it to move downwards and across the bottom and back to the upwind side causing circulation of the entire body of water.

As we move into the warmer spring and summer months, the wind slows down along with the amount of rainfall.  Now the top of the body of water begins to increase in temperature and there isn’t enough wind power to circulate, and the pond begins to stratify.  This happens most often in ponds and lakes with depths greater than 8 feet, and also in secluded areas that are restricted on any wind movement.  A body of water in a wide open field that is less the 8 feet deep will most likely never stratify.   A pond or lake located near lots of trees and wooded area, having depths at 8 feet or more will most likely stratify every year.

A large problem with stratification is that the lower layer of water has little to no way of gaining dissolved oxygen which means it can not sustain a whole lot of life.  Now the fish are forced to live in the top layer.  This can cause major stress on the aquatic animal life.  Also, in the event of a large storm, with enough wind and rain, it can cause the pond to turn over, which can result in a large summer fish kill.

When the late summer and fall months arrive, the top layer will begin to cool down and eventually will be at the same temperature as the lower layer, and the stratification will disappear.  As cold weather roles in, the top of water will become cold and less dense which will cause the body of water to stratify once again.   Most of the time, a strong wind will come through and break the stratification within a couple of days.  Sometimes though, the top of the water will freeze, which will eliminate all movement and the water will remain stratified throughout the winter.  Now with the water stratified, and with the ice and snow blocking any sunlight from penetrating, dissolved oxygen levels become very low which sometimes will result in a winter fish kill.

To prevent stratification, a proper bottom aeration system in the best solution.  When a body of water is properly aerated, there is enough movement to circulate the entire body of water all year round. It is possible to under aerate when there isn’t enough pressure from the bottom to move all of the water. The proper system for your body of water is important and extremely beneficial.