Pond Boss Forums AERATION Should I aerate? Windmill Aeration

PART 2: Is Aeration Really That Beneficial?
In part 2, I am going to provide some quotes from an article that was in Pond Boss Mag. Sept/Oct 1995 written by Elmer Hedlund (deceased) who owned Hedlund Aquaculture in Wisconsin. Preface: When I mention oxygen in this note I mean oxygen from air or plants that is dissolved in the water. Elmer sold insurance for a living and loved fishing & raising fish. He built several large ponds or small lakes. One was 30 acres. He studied & talked to many experts around the country about aquaculture and raising fish. In one of his small lakes, on an island, he built a stream that had the flow powered by one of his aerators. In this stream he had walleyes spawn successfully!
According to Elmer, oxygen is the most misunderstood factor to many pond owners. Widespread opinion is that oxygen is usually only a problem during winter when there could be a fish kill. Note, fish kills are common in northern ponds/lakes that have extended snow cover. However in the south and north, fish kills can also be common in the summer. These fish kills are due to water without dissolved oxygen from the deepest pond areas getting rapidly yet naturally brought to the surface (turnover) where it degrades the top water enough to suffocate fish.

Elmer says "A healthy pond must have oxygen at all levels throughout the year. The lack of oxygen on the bottom of ponds & lakes is causing them to fill up with dead plant matter, and these bodies of water are slowly dying through a process called eutrophication". "This natural but destructive process can be prevented and reversed by providing an ever-present supply of oxygen to the botttom of the pond or lake". Elmer developed a innovative diffuser that he powered by different air compressors depending on pond depth. These diffusers pumped large volumes of water off the bottom to the surface.

Next he explains what the pond bottom is like when it has oxygen all the time.
"In most parts of North Amer. millions of insects lay eggs on each acre of water. These eggs go to the bottom and if the oxygen is present the eggs hatch. The larvae come with their mouths in gear. Most of the larvae will feed on the plant matter." Elmer means dead plant matter of all kinds. This includes plants that grow and die in the pond and dead plant materials that get blown or washed into the pond. However this also includes dead animals usu. invertebrates called zooplankton that grow and die in large quantities in the water column..
He goes on to say "Other insect larvae are carnivorous and eat one another. But they all provide food for the fish. At the same time they consume much of the dead plant matter - which serves to deepen the pond. If fish are present most of the insects are eaten off the bottom of the pond, others are eaten as they come to the surface. But enough insects survive to replentish the population."

Here is the most important part of his article in regard to benefits of keeping oxygen in the water at the bottom, "If the oxygen disappears for even one hour the eggs and larvae die, but a plentiful supply of oxygen will enable the lake to produce up to 1,000 pounds of fish food per acre per year. Aerobic bacteria, phytoplankton, zooplakton and other minute organisms provide an enormous supply of food for the fish in the pond." Without oxygen in the deep water and at the bottom of your pond none of these critters are present. In another article Elmer says that "when all the organisms die it takes a long time to re-establish the living ecosystem at the bottom of the pond". Scientists call the critters that live in & on the pond sediments PROCESSORS because as Elmer says they "eat" or breakdown the dead organic materials into the basic chemicals -earth to earth, dust to dust, kind of thing.
Elmer also fertilized his ponds/lakes. He put fertilizer water in the boil of his aerators and let the currents distribute the nutrients in the water.
You can find out fairly simply if your pond has lost its oxygen on the bottom.
Take your pond's temperature. Measure the water temp. at the surface. Then measure the temperature at or near the bottom. If the temperature is 10 degrees F cooler on the bottom than on the top your oxygen is probably absent. There are exceptions to this example but 9 out of ten times it will be accurate for small ponds esp. if your water visibility is less than 4 feet of depth. The only way to be really positive is to measure the dissolved oxygen in the bottom water. You can buy an oxygen test kit at a good aquarium/pet store. Collect some water near the pond's bottom with a weighted jug and stopper with string atached. Sink the jug, pull the string/stopper, bring the jug to the surface and test the water for oxygen. This will give you a rough idea of how much is in your water.

Basically all ponds lose the oxygen on the bottom soon after the pond stratifies into temperature layers in the spring. As oxygen is lost, harmful decompositional gasses start to increase. These harmful gasses also help to eliminate beneficial living organisms/critters in the deeper waters. In the north usually by Memorial Day oxygen is gone at the bottom from all non-aerated ponds. I've conducted oxygen tests on ponds where the air injection aerator is shut off after a complete mixing. The oxygen at the bottom declines each day until it is back to zero after seven days. It doesn't take long to lose the oxygen at the bottom of the pond during the summer. WITH OXYGEN GONE EVERYTHING DIES IN AND ON THE BOTTOM IN THE DEEP ZONE.
So to answer your question "Is aeration really that beneficial? YES, if you want to keep the bottom of your pond "alive" with critters who provide tremendous amounts of fish food and at the same time digest and quickly break down ALL the dead material that settles to the bottom.
This is especially true if you fertilize your pond because the "bloom" reduces the depth to which sunlight penetrates thus reducing how deep oxygen is produced in the water. The fertilization-bloom also produces LOTS of organic material that settles to the pond bottom each season.
Oxygen is only in the shallow, warmer, upper layer where light is penetrating and the water is mixing. A shallow depth of oxygen production reduces or eliminates the amount of oxygen in the deeper zone. This translates into a smaller "bank account" of dissolved oxygen in the overall pond. This puts the pond in a delicate oxygen balance which results in less room for error in situations where oxygen becomes critical. Fish kills can happen easily in these situations because of the low oxygen amounts in the deeper waters. Whenever the pond turns over quickly - fish die. Note: YOU DON'T SEE ALL THE MILLIONS OF BUGS THAT DIE WHEN OXYGEN IS LOST ON THE POND'S BOTTOM EVERY SUMMER! But you know it has happened when the sediments turn BLACK or see black muck on your boat anchor. For the most part, nothing lives in the deoxygenated, septic, black conditions. Oxygen loss at the bottom can be prevented by circulating fresh water from the top to the bottom by air injection at the bottom. This note was compiled by Bill Cody the Pond Doctor.