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#50723 - 12/09/04 10:07 AM Aeration "Supercooling"
Bruce Condello Offline
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Registered: 08/01/04
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I was talking with a fisheries biologist the other day who stated the following:

"In northern climates I don't recommend winter aeration. The reason for this is that solar energy is absorbed by the dark colored bottom of the pond. Combined with plant and bacterial activity this creates a band of warmer, denser,heavier water on the bottom which is between 36-39 degrees. If you are aerating when the air temperature is less than zero degrees F. you can "supercool" the water that's been brought to the surface to slightly below freezing. This water is then returned to the pond by circulation and you can end up losing this band of warm water that fish such as bluegills and bass like to inhabit. Since cold water in the presence of a healthy plant and algae population is likely to be already high in oxygen why would you bother to use the electricity necessary to aerate a pond in the winter"?

I thought this was an interesting viewpoint, which is probably only applicable to smaller ponds in the northern part of the U.S. and Canada. Does anyone have any comments on this or do you think it's much ado about nothing? I do realize that thick ice covered with several inches of snow can be a contributor to winterkill situations. That notwithstanding the biologist seemed to have a valid argument.
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#50724 - 12/09/04 03:45 PM Re: Aeration "Supercooling"
Pottsy Offline
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Registered: 04/21/02
Posts: 494
Loc: Ottawa, Canada
I think the key is not to put your air stones in the deepest water... thus avoiding much disruption of any potential 'warmer' water.

Without an open air hole to allow gases to escape there is always a risk of them reaching toxic levels during the winter.

I don't recall the last time I saw ice that was clear enough to allow significant amounts of light penetration... at least not enough to replace the oxygen created by 'anchored' plant life with oxygen created by the various free-floating algae.

I know for sure that without aeration I would have zero game fish left at the end of the winter... the longer the winter the more likely of a big kill from lack of oxygen or poor water quality. With rooted plant decay and very little light penetration I can pretty much guarantee my fish would die without aeration. They benefit not only from the oxygen added to the water by the 'bubbles', but by the open area that then allows light penetration and gas escape.

I don't recall the last time I saw ice that was clear enough to allow significant amounts of light penetration... at least not enough to replace the oxygen created by 'anchored' plant life with oxygen created by the various free-floating algae. I can clear some areas of snow but that still leaves at least 18-24 inches of 'patch-work' ice that doesn't pass light worth a darn.
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#50725 - 12/09/04 03:59 PM Re: Aeration "Supercooling"
Bruce Condello Offline
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I like the way you think, Pottsy.

I'm sure that our friendly Texan pondmeisters are having a good laugh at our expense right about now. \:D

Are you suggesting that I could get the best of both worlds by setting up my stones maybe two or three feet off of the bottom?
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#50726 - 12/09/04 04:01 PM Re: Aeration "Supercooling"
PaPond Offline
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Registered: 08/29/04
Posts: 177
Loc: Northern Wayne County, Pennsyl...
Small northern ponds also benefit from the warming effect of the ground, that's why heat pumps work with buried coils, they take advantage of the latent heat in the ground. I would agree with Pottsy that the best of both worlds is to raise the aeration up to the shallower depths to keep open a clear window for photosynthesis, but if airflow is reduced so the mixing is not excessive with deeper bottom diffusion membranes, the water will gain heat from the ground and not stay at the supercooled temperatures. The trick is to strike a balance between natural warming at depth and circulating too much supercooled water. My vote is to keep the oxygen saturated at depth and that means aeration.
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#50727 - 12/09/04 05:07 PM Re: Aeration "Supercooling"
Bruce Condello Offline
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PaPond, I've been reading your posts and I really enjoy the way you present your ideas. Do you have a background in limnology? It sure seems like it.

I'm casting you my highest rating! I hope you're around for a long time because this forum really benefits from viewpoints like yours.

Bruce
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#50728 - 12/09/04 05:08 PM Re: Aeration "Supercooling"
Gainesjs Offline
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Registered: 06/06/03
Posts: 107
Loc: Pacific, Missouri
I would like to hear more opinions. I turn off my aerator for the winter months. The only fish kill stories that I have ever heard occurred during the hotter months - (or possibly a lake turnover in the spring or fall). I figure that if oxygen was a problem in the winter months, then there would be a lot dead fish in the 10,000 Natural lakes in Minnesota. Any other Pondbosses have an oxygen related fishkill occur during the winter? Is this rare or common?
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#50729 - 12/09/04 07:04 PM Re: Aeration "Supercooling"
PaPond Offline
Member

Registered: 08/29/04
Posts: 177
Loc: Northern Wayne County, Pennsyl...
Bruce, why thank you, I don't believe I've ever been rated before, been berated often but never rated. I do have a background in oceanography, my masters is in chemical oceanography and I specialized in marsh nutrient systems. This sweetwater stuff is all new to me. When I finished grad school back in '74 jobs in oceanography were few and far between, now I'm reading Pond Boss and I hear about all these guys who went the fresh water route, from Texas no less! Very encouraging.
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#50730 - 12/09/04 09:42 PM Re: Aeration "Supercooling"
Wood Offline
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Registered: 12/01/02
Posts: 355
Loc: Edmonton Alberta
Interesting topic, and one of the few that I actually have "some" experience with. I think one of the major factors involved here is the fish density of your pond and also the pond's age and amount of nutrient present. The larger the b.o.d. (biological oxygen demand) then the greater chance of some winterkill.As an advantage, colder water holds more oxygen than warm water.
I only have experience with trout, where a warm water refuge is not really an issue for survival so I cannot comment on the pros, cons of that.
Last winter I had 196 days of ice on my pond. Maximum ice thickness was over 30". I did not aerate and had no winterkill at all. This is a newer pond and fairly low density. I did remove most snow cover quickly and routinely.
The one thing I found that did suprise me was the amount of light penetration through very thick ice. Dropping the underwater camera down even with only 6" of snow cover showed almost complete darkness, yet where I kept the snow off was very well illuminated all the way to bottom even with near 3 foot ice thickness. For my purposes, snow removal is key to over wintering trout and not aeration.
Oh, and for you Texans, air temps this morning here were -37c. Tonight when I got home we were at -4c. Gotta like the Rocky Mountains.
Wood

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#50731 - 12/09/04 10:05 PM Re: Aeration "Supercooling"
Brian Loberger Offline
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Registered: 10/29/02
Posts: 208
The worst experience ever with my pond was right after the first winter. We stocked it the first summer with yellow perch, LMB, and hybrid bluegills. By fall we had bass that here 10-12". We left the aerator in the deepest spot on the advice of the pro that sold us the fish and the equipment. All winter we couldn't wait to see the fish in the spring. When the ice receded there were dead fish everywhere. The bass died first and were badly decomposed. The bluegills were completely gone. The yellow perch survived for the most part but were badly stressed. Some of them you could grab out with your hand but they were still alive.

That summer we were blessed with a swarm of baby bullheads and no predators to control them. (they don't show up till mid summer when it is too hot to stock bass). We had algae like you wouldn't beleive from all the nutrients. The water smelled terrible.

We restocked the bass the following spring and caught 362 bulheads by hook and line and trapping. I am starting to regain the balance after 2 years.

Ever since then I have place my airstone in about 3 feet of water. I tie it to a post on my dock. I did not lose any fish last year and hope not to lose any this year. Plus the open water lets me keep my dock in all winter. The song birds like having the open water by the dock also.

To end a long story, do not deep water aerate through the winter in cold climates. I move mine in the fall when the water gets down into the low 50's (around Haloween) and will put it in the deep area once the surface gets over 50 and still I am careful to check the temps every day.

Be careful.
Brian

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#50732 - 12/10/04 10:06 AM Re: Aeration "Supercooling"
Dave Willis Offline

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Registered: 09/09/02
Posts: 2587
Loc: South Dakota State University
Great topic, and one on which I am NOT an expert. However, I am quickly learning by hard experience. I had a few comments that I thought might add to this discussion.

First, I want to ensure that winter aeration is given credit for being a useful technique. When you get sufficiently long winters with sufficiently productive water bodies, there is no way to sustain a fish community without aeration. So, this does NOT apply everywhere, but certainly does in the northern plains states (eastern SD is a good example). There is no way that a 3-acre pond, even 15 feet deep, would sustain a pond fish community through the winter in my locale without some assistance.

Before I continue, I must admit to knowing way too little about winter aeration. I was always taught and passed on the old idea that you put the aerator discharge into the deepest part of a water body. Heck, it made sense! The warmest water is at the bottom of the pond during the winter because water is heaviest at 39 F (4 C). [Without this very unique characteristic, ponds would freeze from the bottom up rather than the top down, and we’d really be in trouble! :-)] So, it made sense to me that you put the air bubbles into the warmest water, and then lifted that water to melt a hole in the ice above. This little factoid obviously was not correct! I also was always taught that direct transfer of oxygen from the air bubbles to the water was minimal. The open hole in the ice allows some photosynthesis and oxygen production, even from the reduced algal/plant community in winter. This little factoid apparently is correct, although I recently learned that direct transfer of oxygen also occurs from the atmosphere to the open-water surface.

The concept that winter aerators should be placed in shallow water has been a great example of how I have learned much from this forum. Let me pass on my “mistake” story.

We had two ponds, one 3 acres and one 7 acres. Both were in grassed watersheds, both were relatively deep (18 ft and 23 ft, respectively), and both were moderately productive, but not overly so. They were far from electricity, so Koender’s windmills were installed, and we put the airstones on the bottom in the deepest part of the pond. The winter of 2000/2001 was a tough one that started early, and ran late. We had snow and ice in October, and so much snow that the ice did not blow clear. Ice-out did not occur until the start of April. What a sad day that was. I walked the shorelines of both ponds, and it was hard to see all those dead 12 inch black crappies that we had developed in the largemouth bass pond. It was similarly hard to look at all those 18 inch smallmouth bass dead on the shoreline of the smallmouth-only pond. The aerators had worked well all winter. During calm periods, the open hole in the ice would freeze over, but as long as there was wind, the holes would open. By the way, a 22-acre pond with 3 windmills survived that bad winter in great shape.

I was sorely disappointed in these winterkills because the ponds were built as well as possible, in as good a watershed as they could be, and the aerators were installed. Based on good input from this Forum, I learned that during a long winter period of circulation, the aeration may result in cooling of the entire water body (under the ice). Too long at too cold temps may stress the fish too much. I also learned that too much aeration may circulate too much water, and allow too much of this cooling to occur. So this lesson is simple: don’t use more aeration than necessary for the size of your water body. There are people on this website far more qualified than I to provide information on appropriate air volume capabilities for various sizes of ponds.

So, what did we do at those two ponds? Well, I suggested to the landowner that he move the aerators up into shallow water, just as has been suggested here.

One of the Pond Boss Forum regulars passed on a publication to me. Theron G. Miller and W. C. Mackay, 2003, Optimizing artificial aeration for lake winterkill prevention, Lake and Reservoir Management, Volume 19, number 4, pages 355-363. I learned a lot from this article, and it certainly fits with the concepts expressed so far on this topic. In this study in Alberta, they found that dissolved oxygen levels actually were better in waters with surface aerators (kept a hole open in the ice) than from aeration units in which the airstone was on the lake bottom. The key was keeping that hole open in the ice. Circulating from the bottom up apparently must have moved some organic material, because dissolved oxygen was always lower in waters with those circulation systems. Finally, this paper actually had some recommendations on optimal sizes of aeration units, based on kW per unit of surface area for the water body.

This may sound funny, but I think we need some more field assessment of aeration and winterkill potential. This winter, I was hoping to get dissolved oxygen profiles from several of the area ponds we manage (ponds with windmill aerators, and some gravel/sand pits that don’t have and don’t need aeration). However, it’s already Dec 10, and there is only a skim of ice on the ponds due to this warm fall we are having. So, it will be a short winter this year! I’m not sure how much we will learn. Good old Mother Nature and her variability!

Dave
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#50733 - 12/10/04 10:40 AM Re: Aeration "Supercooling"
Dave Willis Offline

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Registered: 09/09/02
Posts: 2587
Loc: South Dakota State University
Bruce -- who was the biologist to whom you were talking? This person apparently knows the subject matter, and I'd like to talk with him/her.

Thanks,
Dave
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#50734 - 12/10/04 01:28 PM Re: Aeration "Supercooling"
Ted Lea FOREVERGREEN Offline
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Registered: 01/08/04
Posts: 969
Loc: NA
Dave Willis, very interesting reading. Concerning your post on the fish kill in the 2 ponds I was curious if you did an DO reading anytime that winter. Was wondering if the kill was more DO deprived than water te related. He is the reasoning.If you had ice/snow cover for 6 months that is a long time for DO to be sustained at any favorable level. The Koender with a 7-8 inch round airstone even in 20 ft of water at a full 1.5 CFM (I belive 1CFM is closer) and figuring 1000 GPM turnover would mean that the 7 acre pond using an average depth of only 15 ft would need 24 days to tunover 1 time. This turnover rate would have no effect on water temp to speak of.

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#50735 - 12/10/04 01:53 PM Re: Aeration "Supercooling"
Ted Lea FOREVERGREEN Offline
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Registered: 01/08/04
Posts: 969
Loc: NA
Part 2, (Sorry about the dual posts)My experience in NW Ohio has been that winter aeration with ice cover is needed very little.I monitor my DO level with a YSI DO meter all winter long, Last year for example the ice was clear most of the time and I think this is the key. I had 14 inches of ice most of the winter and never had less than 103% of saturation and a lot of 110% or 12-14 PPM DO 38-42F and would be content with 5-7 ppm .However I will open up my winter diffuser which is a Koender Airstone with 1 cfm of air for the 2-3 days that it takes to punch a hole in the ice if I have a lot of snow cover. I always reccommend a placement of this stone in 3 ft of water.One of my personal ponds is only 2 years old and was filled with well water 1.1 acre (pic at www.cleanponds.com)my smaller pond is 4/10 acre and has 38 acres of ag watershed and is 40 plus years old.(pond on the the right in pic)This pond has a Koender windmill and the standard stone in it for winter aeration and had the same DO levels all winter. The airstone in this pond was left at the 8 ft level last year but probably only turns 300-400 GPM at that level.It did not keep open water much and had water temps in the bottom (8 ft) of about 37-38 F, so not much temp decrease due to over circulation.All ponds seem to winter differently. If DO levels are checked you can access the need to aerate or not.Letting some light in still seems to be the safest way to boost DO levels for those of us in the North.I have more concern about a aeration system that can turn the entire water column over 1-2 times per day than windmill that circulate far less than that.If you monitor your DO levels in the ponds with the airstones either electric or winpowered and they are not acceptable considering doing some research on diffuser selection. Ted

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#50736 - 12/10/04 02:00 PM Re: Aeration "Supercooling"
Bruce Condello Offline
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Dave,

The biologist's name is Aaron Klusmire who is the head fisheries biologist for Natural Habitats Unlimited. He says he was taught by a possible acquaintance of yours named Chris Guy at Kansas State University. If you wish to speak with him his phone number is 402-672-6191. Aaron's help has been invaluable to me over the last several years (and he's a pretty good guy, too). He has been involved in some pretty amazing trout habitat undertakings in Wyoming.
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#50737 - 12/10/04 02:30 PM Re: Aeration "Supercooling"
Dave Willis Offline

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Registered: 09/09/02
Posts: 2587
Loc: South Dakota State University
Ted: Very good points. Thank you!! That is good advice. To answer your question, no, we did not have d.o. measurements. As I mentioned earlier, I need to know more about this topic, and we are planning some monitoring this winter. When the 3-acre pond killed, there was a distinct hydrogen sulfide smell that is typical of the winterkills around here. I know from visiting with an Ohio DNR biologist in Findlay that you folks have one heck of a lot milder winters than we do. Thus, it sure sounds like a person should think twice before undertaking winter aeration. Honestly, though, we’ve got waters that would never sustain a fish community without some open water. Winterkill is a fact of life here, in both public waters and small private waters. Bottom line: we’ll monitor d.o. this winter, and then maybe we can at least ask the right questions! As you indicated, we don’t even know the root cause of the problem right now.

Bruce: Thanks for the biologist update. I appreciate it. Yes, Chris Guy was actually my first PhD student. He’s a gem. However, Aaron learned about aeration systems somewhere/somehow that did not involve me!! :-)

Dave
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#50738 - 12/10/04 03:21 PM Re: Aeration "Supercooling"
Cecil Baird1 Offline
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Registered: 08/08/02
Posts: 20043
Loc: Northeastern Indiana
I've learned about winter aeration from the school of hard knocks too. Some bad advice out there and sometimes people sell you stuff but don't tell you anything. I too aerated in the deepest water with not one but two diffusers my first winter! More is better right? \:o I didn't have a fish kill probably because the pond was so new, but my bass were definintely stressed come spring and some of the biggest ones succumbed to some kind of pathogen, I'm assuming, because their immune system was compromised by the stress. After I stopped that stupidity my fish have come into spring just fine ever since.

I have found here in northern Indiana if you can keep the snow off for the most part you don't need any aeration. However I set up a diffuser in shallow water with a small compressor just in case we get lots of snow before the ice gets very thick. If your ice isn't very thick yet, and you get lots of snow you're screwed if you want to get the snow off the ice. And the gas release thing causes me to crank it up when air temps are above freezing to open up a hole now and then. I do have a really high density of feed trained bass so I may run the shallow diffuer all winter to be on the safe side. I do run a small one in shallow water on the trout pond all winter.

I use a snow blower on my .62 acre pond and believe me the pond looks really big when you have to blow the snow off. However I believe if you take it off in strips you're O.K.

For the one from Missouri --how much ice do you get in Missouri? I know you get an occasional snowstorm, but I would think if your ice doesn't last more than a month you shoudn't have to aerate if you can keep the snow off.

So far a mild winter here too. Had skim ice a couple times on the small trout pond and only once on the bigger warmwater fish pond. But we usually dont' get good ice until around Christmas.
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#50739 - 12/10/04 03:50 PM Re: Aeration "Supercooling"
Shawn Banks Offline
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Registered: 08/20/03
Posts: 288
Loc: Northwest MO
Cecil,

You're assumption about Missouri is correct. I live in NW Missouri and we rarely have ice for extended periods of time. Last year we had about a three week time period with 6" of ice. Overall, I would say that the ice period is highly variable even for us up in the colder parts of the state. Four years ago we had 18" of ice for nearly 1 month. Three years ago we didn't have enough ice to get out and fish. It's just not that predictable here. The longest I have ever seen the lakes locked up is 9 weeks.

We are, however, subject to winter-related fish kills. Trust me. My phone rings off the hook after ice out. Most of these ponds are highly fertile, shallow, and overstocked as you would figure. I give the same advice as others have already posted, keep windows open by removing snow. Our bigger, state managed lakes will occassionally have mild kills.....mostly shad. This is my favorite time to fish for channel cats using shad sides and shad guts:)
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#50740 - 12/10/04 04:26 PM Re: Aeration "Supercooling"
Gainesjs Offline
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Registered: 06/06/03
Posts: 107
Loc: Pacific, Missouri
Pondbosses - Thanks for all the replies regarding winter pond aeration. Very interesting subject. I would gladly pay for winter aeration costs, if I knew it was required. (I wish the O2 analyzers were not so expensive.)
Sounds like more fish are killed by deep water aeration mistakes than if there was no aeration at all.
I do not think anyone has yet posted that they actually measured low dissolved oxygen levels in the winter. Several people have reported winter fishkills, low O2 was assumed, but was it proven by actual measurement??
I would be very interested in winter O2 data reports, especially in the worst case conditions, high fish density, frozen lake with snow, no aeration.
Many Thanks!
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#50741 - 12/10/04 04:35 PM Re: Aeration "Supercooling"
Ted Lea FOREVERGREEN Offline
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Registered: 01/08/04
Posts: 969
Loc: NA
These are really some great posts, I belive some fish will survive the winter because of it !!Yes I agree the DO meters are costly but such a great tool.Perhaps we can get Bill Cody to wade in on this subject some more as Bill has commented on it before (see prior posts)I think everyone agrees that the least one can do is try to get some snow off in strips if on the ice for more than a month.But as Cecil commented if you get an inch of ice and 4 inches of snow you have a problem !!

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#50742 - 12/10/04 07:50 PM Re: Aeration "Supercooling"
Bruce Condello Offline
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Caution!!: Non-scientific comment to follow!

It seems intuitively correct that organisms that are made up of almost all water would favor a little temperature gap from freezing. A fish has a hard enough time fighting off everything else without fighting crystalization of it's slime layer. (Sure, I'm exaggerating, but 39 F. sounds a lot more comfortable than 34 F.) Very, very interesting the previous comment from Brian Loberger about losing his Centrarchidae but having his yellow perch survive. Perch are a true cool water fish, especially compared to bluegill and largemouth which are a little more warm water/fringe fish from an evolutionary standpoint. Could it be that perch, walleye and trout could withstand "supercooling" just a little better?

Again, no data to support this...just a little theoretical guessing. \:\)
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#50743 - 12/10/04 10:02 PM Re: Aeration "Supercooling"
Cecil Baird1 Offline
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Registered: 08/08/02
Posts: 20043
Loc: Northeastern Indiana
Bruce,

I know the trout can as I have run an aerator in deep water in the trout pond with no problems. Could be the the walleye and perch are more tolerant, but it could also be they can handle lower D.O. or a little of both. Trout cannot handle low D.O. very well in most circumstances.

Believe it or not aquaculturists and academics around here are referring to largemouth now as "coolwater" fish. It was not so when I studied fisheries. If you think about it they are a coolwater fish ih contrast to catfish and talapia which have higher optimum temps. I see the AFS now considers the Florida largemouth a different species than the northern largemouth due to DNA analyisis.
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#50744 - 12/11/04 08:56 PM Re: Aeration "Supercooling"
PaPond Offline
Member

Registered: 08/29/04
Posts: 177
Loc: Northern Wayne County, Pennsyl...
If fish can be stressed by the supercooling of the deeper water by aeration, then how do cage culture fish fare when they are essentially trapped in a pen close (within 5 feet) to the surface, where theoretically the water is the coldest. Are there different guidelines for aeration if you're floating a cage of trout or HSB in a northern pond? Since water starts its natural migration to the surface at 39 degrees, and reaches the surface when it is at or very close to 32, the surface waters must be pretty nippy for the caged fish. Are they stressed similarly to the fish supercooled by bottom aeration over the winter?
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#50745 - 12/12/04 08:02 AM Re: Aeration "Supercooling"
Dave Davidson Offline
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Registered: 04/22/02
Posts: 1892
Loc: Hurst & Bowie Texas
PaPond, Bruce, Wood, Pottsy Cecil and others; Please educate me. I'm in Texas and, around here, ice is something that is usually manufactured and water doesn't often get down to 39 degrees except on the edge of a body of water. Your post says that water rises at 39 degrees and real obviously freezes in your part of the world when it gets to the surface. By itself, that makes sense.

However, my ignorance is why the cooler water doesn't sink. I am assuming (dangerous, I know) that water, like air, rises when warmed and falls when cooled. That is why the bottom of my pond is cooler than the top and,to some degree, why we have thermoclines. Now, there is something real basic here that I don't understand. If that rule were always true, ice would be on the bottom of the pond. I realize that statement is an exaggeration and assume that air trapped in freezing water keeps it more buoyant. It seems that 33 degree water would flee from the surface to always be replaced by warmer water. I guess it also begs the question of why water "layers" as in a thermocline. Surface water temp is obviously influenced by air temp. It appears that water should constantly be mixing and a thermocline shouldn't exist. Thanks in advance for answers that most Texans have never had a reason to ponder.

Hey Wood, we have a cold front or what we call a Norther coming in tonight. The temp will plummet about 25 degrees to the 50'sF during the day and will get down to freezing during the early morning. Sure hope it doesn't last long.

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#50746 - 12/12/04 09:24 AM Re: Aeration "Supercooling"
Theo Gallus Offline
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Registered: 05/14/04
Posts: 12400
Loc: Central Ohio
Water is the densest at 39 deg F (4 deg C). It's been a long time since college Physics & Chemistry, but I will try to remember enough to give a better explanation than "Just because."
Liquid water is just that, a liquid. There is no structure between any of the water molecules and their spacing, while much tighter than in the gaseous state (steam), is controlled by how much energy they have and therefore how fast they are moving. The energy is the temperature; the warmer the water, the more energy the molecules have, the faster they move, the farther apart they are. Warmer water means less dense (lighter in weight).
Colder water means less energy, slower molecules, tighter spacing, more dense (heavier in weight). So normally the colder (heavy) water sinks and the warmer (lighter) water rises, which causes the normal Summer temperature gradient that may be seen all year round down South where "Ice" comes out of the freezer.
But when water gets cold enough, it freezes. Ice is a solid, which means the water molecules in it are rigidly locked into position. They have to be lined up in those 60 & 120 degree angle formations that make the characteristic 6 sided figures we know as snowflakes.
Now comes the tricky part. Liquid water doesn't freeze into a solid until it's temperature drops to 32 deg F. But when the water temperature gets below 39 deg F, the molecules start to form up into the 60 degree angle formations. They don't actually get all the way there until 32 deg F, but they start to line up, kind like being tied together with bungee cord as opposed to being rigidly glued together like they will be once they're ice. This semi-structure forces the water molecules farther apart than they were just above 39 deg F, overpowering the closing-up effect that lowering temperature was having on molecule energy and spacing.
So from high temperatures down to 39 deg F, cooling water packs it's molecules tighter and makes it denser. Below 39 deg F, (partial) molecule structure overcomes the energy loss packing, and the molecules grow farther part, making the water less dense. At 32 deg F ice forms, which is less dense (lighter) than water, so it floats. This gives the (northern) winter temperature gradient with the densest, warmest (39 deg F) water on the bottom, the lighter, colder (32-39 deg F) water above that, and the lightest stuff (ice) on top.
If this weird condition didn't occur and ice sank, not only would your pond freeze from the bottom (as pointed out above), the oceans would, too. Studies have shown that they would also stay frozen except for a meltwater layer on top, tying up most of the planet's water and making life on Earth very different, if not impossible.
If there's a real (or just better) physics guy on the forum, you can straighten this out, but that's how I remember it.
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#50747 - 12/12/04 09:26 AM Re: Aeration "Supercooling"
PaPond Offline
Member

Registered: 08/29/04
Posts: 177
Loc: Northern Wayne County, Pennsyl...
Dave, The one thing we all have in common in our ponds is the water, and water acts in a very unique way. Generally water sinks the cooler it gets, and thats true up north as well, the catch is that at 39 or 40 degrees the density of water begins to change, the molecules begin to line up for the formation of ice and in the process become less dense. The closer to freezing it gets the closer they are aligned into what will become the chrystalline structure we all call ice. The alignment process is (or was when I was in college) called the 'pseudo chrystalline state' But think about it, if water didn't behave that way, life as we know it might not be here. Ponds would freeze from the bottom up and a lowly pond is where the whole thing probably started. The fact that water behaves this way, allows the ponds to get a stir, mix the nutrient soup up a bit, and bring the life back in the spring. But then again maybe life began in Texas where the ponds don't freeze and that's why you guys get such big ponds!
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