Sub-surface aeration delivers oxygen to dams, lakes, and ponds, through underwater air-stations, promoting aerobic bacteria that break down nutrient-rich sludge. Using shore-based pumps and underwater air stations, sub-surface aerators circulate water without overly disturbing the surface. Efficient, low-power, and natural-looking, these aerators improve water quality, reduce odour, and support fish and aquatic life.
Summary
Sub-Surface Aeration 101—Underwater Air-Stations
Aeration is one of the best ways to solve many problems we see in dams and ponds, but there are a few different ways to go about it. If you don’t know the basics, it can be challenging to decide between the different types of aerators.
We’re going to run you through everything that matters: why we aerate, what aeration is and does, and the advantages and disadvantages of sub-surface aeration.
Why Aeration Matters
Aeration gets oxygen into your dam, lake, or pond. Why do we do that? We want to stimulate aerobic bacteria. In dams that aren’t aerated, you get a cold water layer about a metre deep, where it’s freezing cold past that point. And it’s not just temperature — it’s oxygen, too. Down at the bottom, you get little to no oxygen. We call this stratification.
That means you have anaerobic bacteria that live in these conditions — bacteria that don’t like or need oxygen. Over time, the dam gets a buildup of leaf litter, animal waste, and all sorts of organic muck that forms a nutrient-rich layer that acts like compost for weeds and algae. The anaerobic bacteria digest this very slowly, but also produce byproducts like methane and hydrogen that you don’t want in your dam.
When you have good aeration, this doesn’t happen.
Aeration: Treat the Cause, Not the Symptoms
Aeration isn’t just a symptom treatment: you get right down and treat the cause of the problem. When you get oxygen down to the dam bottom, you shift the populations of bacteria from anaerobic to aerobic, and the aerobic bacteria will break that waste down much faster.
So instead of it building up over time, it will decrease over time. Because the muck at the bottom is like a compost fertiliser for algae and weeds up above, you cut off the supply of nutrients, and you end up with fewer problems with weeds and algae.
Since anaerobic bacteria also produce hydrogen sulphide and methane, in non-aerated dams you can get foul odours — especially if you’re pumping it out and putting it onto your garden or irrigating with it. You can get that rotten egg smell. Aeration helps remove that smell quickly.
If you’ve ever noticed fish clustering at the top of your dam or pond and wondered how to fix it, aeration is the answer. It’s good for fish because the oxygen only being at the top of the water means that the fish can only live at the top of the water… and that makes them easy pickings for birds. You can’t change their behaviour without changing conditions, and the only way you can do that is with aeration.
Aeration treats the root causes of these problems by getting oxygen down to the bottom, and in deeper dams, that’s where sub-surface aeration systems are really valuable.
What is a Sub-surface Aeration System?
You can think of sub-surface aeration as like a big fish tank aerator. You have a shore-based air pump, and we normally use a self-weighted air hose that sinks down to the bottom of the dam, so there’s nothing floating around on the surface. At the end of the hose are air stations, which come in various configurations and sizes.
These discs release millions and millions of little bubbles from the bottom of the dam. They start very small, about half a millimetre, and as they come up to the surface, they get larger because the pressure reduces. You end up with a vertical column of rising air bubbles. There’s a bit of gas exchange here, but that’s not how aerators aerate.
Aeration happens because the vertical rising column drags all the water from the surrounding area from the bottom up to the top to meet the air — that’s when you get the gas exchange. Then the water goes around and eventually back down to the bottom, circulating the oxygen.
It works like this:
– Bubbles rise and expand
– The rising column pulls deep water to the surface
– At the surface, the water picks up oxygen and releases gases like methane and hydrogen
– Oxygenated water flows back downwards
If you’ve got deeper water, the bubbles will move more water. We recently worked on a dam for a client that was about seven metres deep and three and a half acres. In this scenario, you need about four or five air stations; we chose four.
But in a three and a half acre dam that was only a metre and a half deep, you’d need more air stations — eight, nine, even ten air stations — because you won’t get that same amount of water movement. The bubbles don’t get the chance to grow, so they don’t move the water as well.
Sub-surface Aeration: Pros & Cons
Any system has advantages and disadvantages. You won’t want to use sub-surface aeration in every single setup. So, here are some of the pros and cons of sub-surface aeration.
Pros
– Power consumption: sub-surface aeration uses less power than other types of aerators because you’re pumping air, not water
– No power in the water: no risk of electrocution in swimming dams
– Aesthetics: there’s no disturbance to the surface, so you keep the water body looking as natural as it can
– Remote set-ups: you can have sub-surface systems a couple of hundred metres away from a power supply — and it’s generally the cheapest type of system in this scenario
Cons
– Aesthetics: some people prefer the natural look, but if you do like the aesthetic fountain display, you won’t get that with a sub-surface aerator
– Performance: they generally don’t put as much oxygen in the water as quickly as a surface aerator
– Intensiveness: they’re less intensive than surface aerators, so in wastewater horticultural situations with a lot of runoff, it won’t produce as much oxygen as a surface aerator
The Big Picture
Sub-surface aerators are a great choice. They work well in deeper dams, they’re cost-effective, and they keep electricity away from your water. For some applications, such as agriculture or wastewater situations with high nutrient density, a surface aerator might be a better option.
But for a natural, traditional kind of dam, sub-surface aerators are a great aeration method that does the job and preserves the natural aesthetic of your dam.
Ready to Aerate? Contact Us
If you’re ready to aerate or just want to learn more, contact us. We’re happy to help — we can assess your site, advise, and help design a system that works for you and your water.
