Here's a link to the original thread:
http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=12;t=000100;p=1#000014 ...and here's the text--cut and pasted.
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.
[ February 13, 2007, 12:43 PM: Message edited by: Bruce Condello ]
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Posts: 3006 | From: Denton, NE | Registered: Aug 2004 | IP: Logged |
Cary Martin
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posted February 13, 2007 06:59 AM
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Bruce! You just stole my thunder and my presentation for the meeting!!!
Now I have to rework the presentation
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Cary Martin / Vice President
Aeration Technologies, Inc.
599 East Main Street
Burnsville, NC 28714
www.aerationtechnologies.net 800-609-6385
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Posts: 265 | From: Burnsville, N.C. | Registered: Nov 2004 | IP: Logged |
Cary Martin
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posted February 13, 2007 07:14 AM
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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.
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Cary Martin / Vice President
Aeration Technologies, Inc.
599 East Main Street
Burnsville, NC 28714
www.aerationtechnologies.net 800-609-6385
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Posts: 265 | From: Burnsville, N.C. | Registered: Nov 2004 | IP: Logged |
Theo Gallus
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posted February 13, 2007 07:46 AM
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It's always good when the Winter session of Dr. Condello's School of Deep (Water) Thinking commences.
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Non carborundum illegitimatus!
(totus res in temperantia)
"I read Pond Boss magazine just for the articles!"
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Shorty
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posted February 13, 2007 08:14 AM
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Very good post Bruce!
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http://www.hamweather.net/local/us/ne/sponheinmer+reservoir/wxn470701.html --------------------------------------------------------------------------------
Posts: 675 | From: Lincoln, NE | Registered: Jul 2005 | IP: Logged |
Victor
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Rate Member posted February 13, 2007 09:53 AM
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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...
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What is man without the beasts? If all the beasts were gone, man would die from a great loneliness of the spirit. - Chief Seattle
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dave in el dorado ca
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posted February 13, 2007 12:00 PM
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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?
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D.I.E.D.
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Posts: 794 | From: el dorado ca | Registered: Apr 2006 | IP: Logged |
Bruce Condello
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posted February 13, 2007 12:20 PM
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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.
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Posts: 3006 | From: Denton, NE | Registered: Aug 2004 | IP: Logged |
Shorty
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posted February 13, 2007 12:33 PM
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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?
[ February 13, 2007, 02:24 PM: Message edited by: Shorty ]
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http://www.hamweather.net/local/us/ne/sponheinmer+reservoir/wxn470701.html --------------------------------------------------------------------------------
Posts: 675 | From: Lincoln, NE | Registered: Jul 2005 | IP: Logged |
ewest
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posted February 13, 2007 01:08 PM
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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.
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Ichthyusiasts read Pond Boss Magazine
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Posts: 3528 | From: Miss. | Registered: Mar 2005 | IP: Logged |
Shorty
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posted February 13, 2007 01:37 PM
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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.
[ February 14, 2007, 04:41 PM: Message edited by: Shorty ]
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http://www.hamweather.net/local/us/ne/sponheinmer+reservoir/wxn470701.html --------------------------------------------------------------------------------
Posts: 675 | From: Lincoln, NE | Registered: Jul 2005 | IP: Logged |
Bill Cody
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posted February 13, 2007 09:05 PM
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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.
[ February 13, 2007, 10:11 PM: Message edited by: Bill Cody ]
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Keep This Forum Viable, Read Pond Boss Magazine
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Posts: 2733 | From: Malinta OH | Registered: Apr 2002 | IP: Logged |
Shorty
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posted February 14, 2007 08:41 AM
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quote:
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The circulation pattern is sometimes affected by wind and waves.
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Absolutly, but it's several dead calm nights in the heat of the summer when the algea is blooming hard that I worry about. 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.
quote:
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Shorty mentioned "Notice the shaft is at a 45 degree angle creating current on the bottom." I ask, how deep is the bottom?
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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.
[ February 14, 2007, 04:43 PM: Message edited by: Shorty ]
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Posts: 675 | From: Lincoln, NE | Registered: Jul 2005 | IP: Logged |
Bruce Condello
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posted February 14, 2007 05:24 PM
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Is this worth archiving?
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Posts: 3006 | From: Denton, NE | Registered: Aug 2004 | IP: Logged |
Theo Gallus
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posted February 14, 2007 05:33 PM
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Yes
[ February 14, 2007, 06:33 PM: Message edited by: Theo Gallus ]
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Non carborundum illegitimatus!
(totus res in temperantia)
"I read Pond Boss magazine just for the articles!"
