Pond Boss Forums AERATION Should I aerate? Aeration simplified

Let's talk a little about what aeration really is.

There has historically been a misunderstanding about what it means to aerate a pond. When I strike up a conversation with a pond neophyte they will commonly talk about aeration being a priority for their new pond.

The most common comments are that a pond needs aeration so the fish can breathe, and that the best ways to do this are with a fountain or a diffuser. Bubbles equal oxygen, right?

Not so fast...

Let's start with some simple water physics.

Things diffuse into and dissolve into water. Water is the universal solvent. Air dissolves into water.

The percentage of oxygen in air is 20.9476 %

Oxygen will move across the "air/water interface" (remember this term ) until it reaches saturation.

Saturation is the measure of how much oxygen water will hold at a certain temperature before it starts to spit oxygen back out into the atmosphere.

Salinity also affects how much oxygen it takes to saturate water. Higher salinity means water holds less oxygen.

If water is less than saturated it wants to take up oxygen out of the atmosphere and this is, in turn, good for fish.

When you put a diffuser on the bottom of your pond and bubbles start to come out of it, the fish really aren't interested in gulping the bubbles. What they really want is the pure oxygen that's diffusing out of the bubble across the "air/water interface".

In high school physics class we learned that lots of smaller bubbles have a lot greater surface area than a few big bubbles. That's why a good diffuser makes the bubbles as tiny as possible. Lots more little bubbles means more surface area, which means more "air/water interface", which means more oxygen diffused into the water for the fishies to use.

Make sure to get a good diffuser. This helps. But what a bottom diffuser aerator system really does is brings a big column of water up from the bottom so that the unoxygenated bottom water gets a chance to gulp some oxygen from the gigantic "air/water interface" at the surface of the pond. This produces a lot more usable oxygen than the bubbles themselves.

How else can we increase this "air/water interface"?

Waves are a good way. I'm sure it is intuitively correct to all of you that a wavy surface has a lot more surface area than a flat surface. Big ponds and lakes usually have more wave action. This means they are not as susceptible to universally low oxygen levels as a pond. That's why we rarely need to oxygenate a 200 acre body of water. There are lots of 200 acre water bodies that would benefit from aeration--just not as many critical oxygen crashes as there would be with a one acre system.

Waves are good.

What's another way of increasing the "air/water interface"?

How about circulation? If you stir water by using, for example, a circulator, the oxygen is constantly jumping into the water from the atmosphere to saturation, then that surface layer is pulled down and replaced by another layer of less than saturated water, which then becomes saturated, again and again and again.

This brings up an important point.

If you have a pond that is completely devoid of oxygen because of an algae crash or some other such disaster, the water at the very, very, very surface is actually saturated with oxygen. That's why fish pipe at the surface to try to survive. The problem is that the saturated layer is only about one molecule thick. Trust me on this one. I found this out from a college instructor who told me that this isn't enough for a fish to survive. Everything below this is robbed of oxygen so the fish probably won't make it. That fish either needs plants to be producing oxygen from below, or enough oxygen mixing from above to adequately support their life processes.

That water either needs mixed from the big vortex formed by a nice bottom diffuser system, or a circulator or a thriving plant community.

What I'm really hoping to do is stimulate a little discussion from some of the aeration experts who know lots more than me. Just hopin' to start a little something.

Bruce! You just stole my thunder and my presentation for the meeting!!!

Now I have to rework the presentation

As I tell all of our clients, aeration is NOT a cure all item or tool in the proverbial aquatic tool box.

It is a very STRONG air tool (lets say equal to an air impact wrench to a mechanic) but other things play into the mix (punn intended) when aerating a waterbody.

Infact, the water/air interface is where all the magic is happening. The O2 transfer is less than 5% from the actual bubble.

I just visited a site that we installed 15 diffusers on (45 acre lake). The lake manager stated that there was a trend of increasing visibility over the past 3-years. From 12" to now 3+ feet using the secci disc.

This has translated into positive beneficial plant growth, increased freshwater mussel populations and a benthic layer alive with organisms found in mesotrophic lakes and ponds.

This lake uses an integrated approach using selective herbicides, triploid grass carp, physical removals, bottom aeration and horizontal circulators for dead end canals.

They have also pushed the city to install collectors or leaf traps in the stormwater outlets prior to discharging into the lake.

All of these equal a healthy lake.

As for the physics, what you posted Bruce is excactly happens. We use the bubbles as a lifting apparatus opposed to actually transferring oxygen. There are cases where the bubble transfer for example the TVA (Tennessee Valley Athority) pumps pure oxygen down to a series of diffusers at the bottom of a dam to increase the oxygen levels at a depth of 100 foot plus but that is not the standard.

Circulation, light penetration, a healthy plant population, a healthy bacteria population and removal of excessive nutrients are all the key to a good healthy lake or pond.

It's always good when the Winter session of Dr. Condello's School of Deep (Water) Thinking commences.

Very good post Bruce!

Great 3000th post Dr. Bruce! I am curious about the efficiency of circulation versus bottom diffusers and aeration as it relates to DO throughout the entire water column. I read your previous post about DO throughout the entire column after just circulating and it caused me to consider circulation over aeration. Does circulation use more energy than aeration? Is it more effective even though it consumes more energy? Is one better for different types of fish than another? Does one effect temperature at depths more than another?

So many questions...

dittos from el dorado, bruce, nice post for #3,000...

victor, i think yer question might highlight the biggest difference between bottom diffusers and circulators like the ones bruce, dwight, and shorty use. circulators dont affect the thermocline as radically as bottom up diffusers do.

so here's my weak attempt at a comparitive analysis, posted for the experts to shoot down.....(actually wondering if we can make a list of generalizations):

circulator - disturbs water surface more and thus fights FA growth better than bottom diffuser,
-doesnt mix water column as efficiently and leaves O2 dead spots in deepest areas of pond,
-not as effective at breaking down muck accumulation
-protects thermocline better which is most important in winter (i.e. does not completely destratify pond)
-contributes to greater evaporation rate in summer months
-on average, uses more electricity?

bottom diffuser - provides more oxygen faster to the deepest areas of pond because the mixing of the enitre water column is achieved faster,
-does not disturb water surface as much, so doesnt fight FA as well
-fights muck accumulation better
-destroys thermocline, and completely destratifies pond
-can potentially harm fish by cycling the anoxic muck up through water column and rapidly raising temps
-contributes some to evaporation during summer months, but not as much as circulator
-on average uses less electricity?

There's only one thing about Dave's post, and it's probably just a matter of semantics. I would say that a bottom diffuser doesn't neccesarily provide oxygen faster than a circulator if you're thinking about initial effect right after setup. If I remember some of Cary, Ted and Sue's great posts correctly there is a lag period after setup of the bottom diffuser where oxygen temporarily decreases as the anoxic bottom water and all of the bad gasses get lifted into the water column.

I'm also paraphrasing the experts here, but it is my understanding that you get a lot more water movement per dollar spent with a bottom diffuser because you are using the lightness of air to lift the water. Once you've paid for the energy to drive the air below the surface of the water, physics takes effect and air has to go up. That is essentially free energy.

On the other hand, if you set up a circulator at the edge of a pond, and it's properly positioned, it can spin the water around the pond and effectively use the momentum of the water coming from behind the circulator.

My uneducated instinct says that the cost per unit of water moved each unit of distance is significantly cheaper with a bottom diffuser.

One comment, bottom diffusers typically just aerate around the area the of the bubble column, the deeper the diffuser is set the larger the surface area is aerated. With a horizontal circulator you are continually moving the water sidways in one direction and should be able to aerate much larger surface areas but not aerate as deep into the water column, does this sound right?

This should be a great exercise in learning. Cary makes an important point that has application to many pond management functions in addition to aeration ( feeding , fertilization , liming , pond turbidity fixes , stocking methods , pond assessment methods, weed management and more ) EACH IS A TOOL IN THE POND MANAGEMENT TOOLBOX TO BE USED PROPERLY. The point --- A chain saw is not the tool to use to fix a faulty power outlet.

A couple of thoughts to ponder.

1. Effect of bottom diffused air aeration on plankton blooms and the food chain during warm water and cold water periods.

2. The many types of aeration (not just circulators and diffusers) and their purpose (pond bottom clean up or avoiding the dreaded 15 min. of low O2}.

3. How the physics of pond size and shape (including bottom configuration) effect your efforts.

4. How carrying capacity and or feeding effects the need for aeration.

5. The right time, place, method and manner of aeration.

Here is one method used in commercial pond management systems.

Here is ours:



The specifications claim that these add 2.5 lbs of dissolved oxygen per hour per aerator. Notice the the shaft is at a 45 degree angle creating current on the bottom.

Comments about some comments. Shorty stated - "bottom diffusers typically just aerate around the area the of the bubble column". Not completely true. Technical discussions about bottom aerators typically mention - turnover or turnover rate which means how often the entire water body will go through one complete circulation - bottom to top. The circulation pattern is sometimes affected by wind and waves. Sometimes the circulation does not involve the complete water column/volume but varying widths of the pond surface and basin. Testing verifies complete circulation. A complete circulation usually involves mixing and distribution of the available dissolved oxygen which can be increasing or decreasing depending on prevailing conditions such as size and number of bubbles, depth of the water column, amount of incident light, temperature, amount of plant biomass i.e. photosynthetic rate, etc.

Shorty mentioned "Notice the shaft is at a 45 degree angle creating current on the bottom." I ask, how deep is the bottom? I assume that all the downward force that the circulator is able to produce has a limit as to how deep it can penetrate? This limit is probably due to several physical factors, one of the main ones is probably horsepower. Additional ones are probably water mass (density) and inertia.

Absolutly, but it's several dead calm nights in the heat of the summer when the algea is blooming hard that I worry about, it's that 15 minutes of no DO that worries me. In a scenario where there is no wind and waves present a bottom diffuser is much more limited to the immediate area surrounding the bubble column that it is aerating. In smaller 2-3 acre ponds they are very capable of turning over most of the water in the pond, in a much larger pond like ours a single diffuser can only create a realtivley small refuge area. The DO crashes we have expierenced have almost always involved dead calm conditions for several days in a row before the crash occured. The one crash that did't involve calm conditions was copper sulfate induced. The last DO crash we had was localized to just the shallow weedy area of the pond after a stong cold front came through and a sudden algea die off occured.

In that picture, 7-8ft, minimum operating depth of this type of aerator is 4ft, otherwise it digs holes on the bottom and suspends sediment in the water. There is a boat prop on the end of the shaft that spins at 1750 RPM's per minute, a 2-1/2" hole at the top of the tubing allows air to be sucked in and spun out through the center of the prop. It does create a deep circular current along the deep weed lines around our 9.9 acre pond. In the picure I posted those aerators are on the north side facing west, 150 yards straight south of the aerators the deep water weeds are consistantly being laid over and are pointing in the opposite direction to the east in 8-9 ft of water. Now if I could turn over most of the water column in our 9.9 acre pond with one or two bottom diffusers I would, at the moment horizontal aeration seems to be the best answer for us. So, the size of one's pond does matter when looking at aeration options. I did check their website and this type of aerator is suited for ponds up to 15ft deep. Keep in mind that the company that makes these is is primarily in the the business of manufacturing aerators for waste treatment plants, their pond aerators are just a scaled down version of the commercial units they make for WTP's and are not their primary line of business.

Is this worth archiving?

Yes

Just to add to this interesting topic, we make a unique aeration tubing that is used for shallow application, it is called Bubble Tubing.

Imagine a soft keeled kink free PVC tubing (ballast)fused to another soft PVC tubing with fine holes on both sides. The size of bubbles is similar to the Vertex disc. Every twenty feet section is worth about one disc with 1000 holes. We designed and developed this product to create aeration (which is more like circulation and turn-over)for shallow application where regular methods are not optimal.

Where creative layout and good design is used, it does create movement of water in dead zones. Works with low pressure pumps like linear for small ponds, but is designed to work up to 50 psi for deeper application. We found that aeration works best when each individual lenghts are not exceeding 200'.

Another comment about Dave, I have yet to observe that this method or the Vertex CoActive airbases cycle sediments. In fact, sediment disturbances are observed during installation sometimes for up to 20 minutes. The term "destroys" thermocline is a bit negative, because in many cases, the thermocline is the reason anoxic condition appears in near bottom. Destratification, when used appropriatly is an excellent, inexpensive method of preventing phosphorous to be released from sediments... huge topic! Keep it up, I love it!

Bruce we very much need an aeration thread archived. Once you do I will find some good threads to link to the aeration topics you and Bill think best . For example winter aeration , the dreaded 15 min rule topic , aeration start up and one of Ted's on his experience measuring DOs in small ice covered ponds , and I am sure others.

OK, well I've gone ahead and did my best to put it in the archives.

Let's start linkin' the heck out of it.

Welcome, Mario! We're interesting in any aeration information you'd ever like to add. Have you seen the magazine yet? It's a great place to advertise products.

M.Paris,

If a single disc from Vertex has 6600 .5mm cuts, how is your 20' section equal to one disc? Who has tested this product? Do you have any test done yourself? What is the turnover rate at depth? How much cfm per foot is required and what size are the holes where the bubble is released?

There are also cases where you want to keep the thermocline when cold water species of fish are desirable and we do not want to increase the temperature from top to bottom.

Hi Bruce! Thanks, I have been advertising in the magazine for a few issues already under Canadianpond I believe we were not in the latest issue but we have been from mid summer till winter last year. Our ad was on the page of the Pond Boss Resource Guide.

Cary, I appreciate your questions, I have a Vertex disc on my desk and counted a total of 2900 holes, they may have changed them since you worked there? We have designed and developed this product over the last 3 years and do not have all the answers yet, what we know is that we have the same size bubbles (.5mm cuts x 48 per foot). So if I recalculate we release the same amount of bubbles than one Vertex disc per 60 foot length of Bubble Tubing.

For rates, we have calculated that the optimal range for CFM/ft is 0,02 to 0,045. When we calculate turnover rate, in deeper water (8' or more), we use Vertex' Air lift technology. Like I said, this tubing is not for every application, but mostly allows for a distribution of aeration and circulation over a larger area in shallow application. In fact, up here we sell a lot of this product for deicing docks, traditionally in shallow water.

About thermocline destratification, where you are located you are at the southern range of trout habitat, temperature being a major limiting factor. Up here, most ponds are trout habitat, breaking thermocline in those may mean being able to keep your fish alive, and prevent anoxic conditions and related side effects. But that is too general because each lake and pond are unique and aeration should be carefully evaluated. We even observed anoxic condition under the ice in sediment rich lakes, which prevent trout to survive winter as well. I have experience with winter kill and summer kill and they are not always predictable, mostly preventable with proper aeration techniques. Actually AquaKler seems to be a good fit for sediment aeration bellow thermocline or under ice conditions if circulation of water is not the objective.

Thank you for the clearification Mario. They must have changed things, heck it has been three years since I have worked there.

I would like to do more work with your product line in the future...Maybe this spring.

I agree with you on the thermocline issues especially in your zone where the surface temperature is not such a drastic difference from the bottom.

We will be working with the AquaKler product this season on our trout ponds too.

Im going to have to read this whole thread again.Its too much info too fast(maybe because Im drinking coffee instead of beer!).But I think bottom diffussers are much better...cause THATS what I spent my money on!!!!Just kidding..great thread and info

I have combined Canadian Pond's Bubble Tubing with our systems in cases where you want aeration or water movement on a shelf or narrow/shallow area of a pond as well as the deeper portions of the pond. For instance a system with 3 air lines, two leading to diffuser disks and one line connecting to bubble tubing.

Sue,

What was the scenerio? Did it reslove the weed/oxyen/algae problems that were occuring?
How long was the bubble tubing? How much psi and cfm did you have to feed to it? Did you use XL or standard AirPods on the other two diffuser locations?

Just trying to get a grasp on the results that can be expected from the bubble tubing.

I think it would be a great tool in those areas of a lake, pond or canal, but just have not heard from anyone using it.

Cary,
Tell me if I'm wrong, but I thought you recomened bubble tubing on this forum last May. You had it on your website, too, under a different name - "AnchorLine SH" - it looked exactly like Mario's tubing - no?