Can Pond Aeration Help Reduce Phosphorus?   

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Written By Mark Washburn

Mark has 20 years of experience as a professional pond management consultant.

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Can pond aeration help reduce phosphorus?

The answer to that is yes.

Aeration, particularly at the bottom of the pond, can increase oxygen levels where it’s needed most.  As we’ll discuss in this article, higher oxygen concentrations can affect the level of phosphorus in a variety of ways.  From improving sequestration of the nutrient in the sediment, to supporting beneficial microbes that can actually consume both phosphorus and nitrogen.  Any reduction in these nutrients is helpful in limiting algae blooms.

Why Phosphorus Reduction Is Important

Phosphorus is a primary driver of algae blooms and when you are able to reduce it in a pond environment you can often limit or even eliminate blooms from happening. It’s important that you consider phosphorus and nitrogen as the two primary drivers of algae and why you have problematic blooms in the first place.

If a pond is struggling with ongoing algae problems, the focus for improvement and ultimately, prevention, should be directed at nutrient management.  And aeration has the potential to support the biological processes in the pond to such a degree, that we usually consider properly fit aerators as the first step in improving a pond’s condition.

What Kind Of Aeration Works Best For Algae Problems?

When we talk about aeration, there are different types of aerators used in ponds. There are surface based pond fountains and pond aerators, and there is a bottom based type of aeration system as pictured here.

When we’re trying to improve a pond environment, particularly with algae, it’s not to say that a fountain aerator would not have any effect, but if the pond has much depth to it, keep in mind that surface based aeration will only affect, say, 4 to 6 feet down in most cases.

If the pond is deeper than that, you may not increase oxygen that much using something from the surface. So, in most cases, we’ll look at diffused bottom based aeration. This is made up of a land based pump. It has some airline that connects to a diffuser that sits at the bottom of the pond. This diffuser will have a membrane on it where air is pushed through it, creating these very fine micro bubbles.

These bubbles rise to the surface. Break the water tension at the surface and allow oxygen to come in from the atmosphere. And then along with that, it also will force this oxygenated water down to the bottom of the pond. It circulates it and mixes it very well from top to bottom. So you increase oxygen levels from the top of the pond all the way to the very bottom and it’s very effective at maintaining good oxygen levels throughout the water body.

Higher Dissolved Oxygen Levels Support Healthy Pond Bacteria

This is important.  By increasing dissolved oxygen levels in a pond, aerobic conditions are promoted. This increase in dissolved oxygen, supports beneficial microbes that are primarily aerobic, and they thrive in these kind of oxygen rich conditions. These microbes are the pond cleaning mechanisms that nature uses to break down organic material.

They  help to consume phosphorus, nitrogen, and to out compete algae for such nutrients, and when those bacteria are thriving you tend to have a much cleaner, healthier ecosystem that stays cleaner longer over a number of years. These bacteria are naturally occurring, but they also may be supplemented in certain cases with commercial products that help support this work, much like a probiotic would be used by you and I.

Bottom Aeration Supports Better Phosphorus Sequestration

In well oxygenated water, iron and other minerals can also react to phosphorus, and it forms an insoluble compound, or encapsulates the phosphorus to precipitate it out of the water. This effectively removes phosphorus from the water column, and in doing that, it prevents algae from utilizing it as fuel.

In anaerobic conditions or an environment that’s lacking in oxygen, phosphorus can actually be released from the sediment at the bottom of the pond. And when oxygen levels are improved, then this release is minimized or slowed and in some cases even reversed to where you can actually start locking up the phosphorus at the bottom of the pond.

Phosphate Binders Can Be Useful Too

The other tool that may be used in some cases is called a phosphorus binder, or a phosphate binder. These are products which are produced that bind to the phosphorus molecule.  They encapsulate it or make it clump together and then, like many binders, it will basically create a compound again, where it gets so heavy that it’s pulled to the very bottom of the pond and in effect sequestered down there.

However you can get the phosphorus out of the water column, through aeration alone or in combination with some kind of binder, it may help manage algae issues just simply by doing that. It’s not necessarily a slam dunk in every case, but it’s moving the pond in a much better direction when you can do that.

Healthy Aquatic Ecosystems Depend On Good Dissolved Oxygen Levels

Higher oxygen levels supported by aeration can also promote the growth of beneficial plants. Things like diatoms, for example, which are generally highly preferable compared to something like a blue green algae, which could be toxic. There are many microorganisms in the pond that actually can utilize some of these nutrients for fuel and sustenance, and many rely on good oxygen levels to thrive.

These microorganisms are actually also utilized by fish. And they represent a very healthy environment, not only for… the balance of the pond, but for the inhabitants of the pond as well. Aeration typically supports all of that very well.

High Phosphorus Leads To Persistent Algae Blooms

Phosphorus, as I mentioned, is a key driver of most algae blooms. When you reduce phosphorus levels, algae will also often go down or be mitigated or even be prevented in some cases. The interesting thing is that when algae starts, when it blooms, and let’s say you have no aeration in the pond at all, it actually can pull oxygen from the water.

It can deplete oxygen, which is one of the reasons you often find fish kills in ponds during hot weather that have very large algae blooms. Algae or any plant, can actually increase oxygen during the day, but the same plant will pull oxygen at night, and in hot conditions, can oxygen crashes much more likely. What’s interesting is when algae does pull oxygen from the water, it can precipitate the release of phosphorus from the sediments, thereby sustaining its life cycle.

I find that very fascinating. It’s not such great news for a pond owner!

Why Mixing The Water Is Important

Effective aeration will obviously increase dissolved oxygen in the pond, but they will mix the water as well.   You want this to occur because it’s the only way to saturate the lower or deeper part of the pond with oxygen.  As I stated before, surface based aerators and fountains do mix a bit, but it’s very limited at the surface.

A bottom based diffused aerators like we profiled earlier will mix the entire water body from top to bottom. As you increase oxygen levels, especially down at the bottom, you can limit the release of nutrients from the sediment in the pond. And that’s just very, very helpful.  Improving the mitigation of phosphorus and nitrogen is the foundational key to limiting algae blooms.  Its as simple as that.

On a side note, this mixing aeration also allows fish to utilize the entire water body rather than just a very limited area of water with life sustaining DO (dissolved oxygen) levels.  In un-aerated ponds, this is usually very close to the surface, its a very limited area, and the hotter the weather gets, the more limited that oxygen availability becomes.  So aeration helps protect fish especially during very stressful times of high summer heat.

Aerobic Pond Bacteria Take Phosphorus To The Grave

Before we close this article out, here’s one more interesting fact about beneficial pond bacteria.  The increase of dissolved oxygen promotes the growth of these aerobic bacteria and they will pull or incorporate phosphorus into their cells. Now these bacteria, like all living things, will eventually die. But when they die, they take that phosphorus with them. And it is still not available for algae to utilize.  Over time, these bacteria will break down and be consumed by new or fresh microbes…along with other organic compounds in the pond.  So not only do you get a fairly quick assimilation or lessening of phosphorus and nitrogen levels in the pond, which can have a direct effect on an existing algae bloom, over time the microbes will help break down the decayed dead plant matter after the die off.

They truly are nature’s clean up crew!

So, in summary, we can come at this from a number of different angles, but increasing the dissolved oxygen levels in a pond helps with phosphorous reduction by promoting aerobic conditions that lead to chemical reactions that lock phosphorous in the sediment.  Improved oxygen levels encourage the biological uptake of phosphorous by microbes, preventing algae blooms through nutrient mitigation and improving overall water quality as well. The improved circulation from the aeration fights stagnation in the pond which is a great help to fish and the microorganisms that live in the pond.

This multifaceted approach to managing phosphorus levels makes proper aeration a very important tool in maintaining healthy pond ecosystems.

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