Well, Craig, as it is a topic very relevant to many ponders across the world, it is probably well worth examining the 'options' that ponders are faced each Winter, I have to remind myself to be ready for the worst.
Sub zero weather, weeks on end. Maybe -10°f to 20°f typical here, weather systems straight from the Arctic via Ohio, though slightly less time exposed to them. Quite possibly power failures for days at a time...
The 'professor' at Ohio seem to have failed to mention, a simple hole in the ice is reliable. Sub zero air does not transmit through ice (don't ask me why, it does not, some scientist will probably explain, ice can get no colder than 32°f)
So, if you drop the water level half an inch or so below the ice, when ice is strong over a pond, the water surface stays more or less ice free, toxic gases can aerate with just one or two intsy wintsy vents.
Voila, no toxic build up. Water surface is ice free, no oxygen depletion. Plants photosynthesise fine, less ice depth, plant freeze damage minimised. Apropriate for ornamental planted ponds where spans of ice can be stable, not lakes.
When you peer through the vent, you can see the fish, peeking back up at you... With fish requirements of oxygen in Winter being 8% (so fish keepers quote, Roark?) of Summer requirements, and inverted water capable of holding more oxygen than in Summer, oxygen depletion is not much of a factor. Well, it wasn't to the 30 fish under that ice on a 120 sq ft pond two feet deep. They came through two weeks plus sub zero in fine fettle, when the majority of other ponds were being wiped out.
Now, when you have your thick strong layer of ice, you can have another blanket of thermal insulation on top of that, snow, to further insulate sub zero air from the insulated, ice free water below the ice
You can sweep say a 20% area of the snow if the freeze is likely to last weeks, not always important as quite often there are 'bald' areas of ice where the snow does not settle which lets light through to keep the plants doing their little bit of photosynthesise (instead of dying en masse in a black out with some air bubble working in an insignificant corner doing very little but thicken the ice and squirt bubbles in a small insignificant area)
You can test how thick the snow can be kept, by physically measuring how much snow it takes to block out light, over four inches or so (no special equipment needed, just hold a clear plastic bag of snow held to the light)
So, the vent:
1) Stops the ice thickening at a desirable thickness to become an ice shield over the ice free surface
2) Snow can be used to further insulate most of the pond
3) snow can be partially cleared to provide light, to ensure plants do not fail
4) The ice stopped at 4" thick? does not continue to cause further freeze damage to aquatic plants further reducing pollution if ice depth had gone on to be much thicker, without the air cavity
(A similar effect to ice double glazing is achieved by putting a structure over the pond, to catch the sun's rays, it can eliminate ice in the covered area)
>>Yet you imply these people you have selected as your experts substantiate your claims...something I failed to discern in my readings of the site.
There are folk there who can clearly calculate the risks and apply aeration to best advantage, they have significant experience, my claim is they appear to be competent and have professional track records. Yups, if you ferret through the search feature, you will find statements discussing the need to calculate the risk from oxygen depletion and toxic sources, to gauge the depth of the body of water as to whether aeration will be effective or not
I do notice folk there valuing the inversion layer, using it to advantage, and being cagey about cooling deeper water, which is something I've noticed. For years. Especially when I keep finding turtles hibernating a few inches below the hypercline. Sometimes they are dinky little turtles, other times they are huge snapping turtles, peering up through ice, waiting for Summer...
I do not know how effective a bubbler is in shallow water, so I don't comment, other than knowing bubblers can and do fail from ice crystals forming within the pipe, power failures etc. I can only estimate that the turbulence will mix sub zero air to increase super cooling in the surface water, likely to spread under the ice and thicken it. I don't plan on doing anything likely to fail, or drive cold water deeper...
>>Just how cold is it in the example you offer that some water will freeze to 18" in a week, but stop at 3" in the pond in the diagram?
Ice freezes at about the rate of an inch a day, after a couple of weeks of freezing... do I want ice 14" thick, maybe more in two weeks time on a two foot deep pond
Or do I stop it at four inches thick by creating an air cavity below the ice... Bear in mind there are big heavy tubs of plants at the water level taking the weight of the ice on the ponds here, so there are no spans of ice more than 10'
>>And the "fifty something water" you claimed to have encountered in a pond with an iced over surface in your first posts...that too seems now to have disappeared from your "observations". Can you explain that to me?
I've noticed ice on the pond half and inch thick. The air is 15°f, two foot down the thermometer is 52°f. Late Summer ground warmth, the effect of ground springs, maybe added to by the warmth from decaying mulm...
Also, late Spring freezes in a warm Spring, not likely to be significant other than to the few frogs that were killed, water too warm to hibernate, no air for them to breathe. Not a predictable problem, big differentiation between air and water, to be observed occasionally with the change in season
Factors which make 'theories' not always predictable...
>>So surely you can see that while observations can be useful, they can also be deceiving and unsupportable
Sure, I get to observe other folk having a lot of casualties, year after year. The novelty of other folk having wipe outs by the pondfull, after depending on pumps and junk wore off a long time ago.
When it comes to using aerators in ponds, I'd listen to experienced folk on pondboss.com, who appear to be reliable, trustworthy and have extensive experience on the subject. But that, is only an opinion of course, of someone who has noticed the difference....
Of course my position changes, when relevant information or data becomes apparent comprehending different scenarios, different ponds. The effect of ground warmth and ground springs is something I'd be curious to know better. The impact of massive die off of algae under ice etc...
It did not occur to me that Roddy Conrad was not familiar with natural ponds, he is certainly familiar with matters significant to fish ponds, the risk of cooling deep water and covering a pond, which is more reliable, and cost effective than the 'Professor's' opinion...
Joyce, I strongly recommend your 'clients' read message boards such as pondboss.com, if only to find out what the real calibre of professional, competence is like among folk in the landscape and lake management industry
Regards, andy
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