Pond Boss Forums INTRO Questions & Observations What Temp Differencial Makes a Pond Turn Over?

I took temperature readings up and down, all around my 2 acre, 15' deep pond today. I got readings between 74* degrees and 77* degrees. I am aerating with my Gast pump and a soaker hose which seems to be doing the job, but my question is, what temperature differencial makes a pond turn over?

OK, Double-camp. You're gonna have to use your imagination a little bit here.

Picture yourself deep underwater. You're in your own pond and you're 14 feet down. It's summer time and there's a big ol' high pressure system that's been delivering 99 degrees temperatures, but the water is cool and heavy. Look around. You don't see any rooted plants. It's too dark for plants to grow. You don't see any live algae even. The light is too thin for even single-celled plants to grow. What you do see is crud. Lots of it. Dead algae from above is drifting down, dead leaves, chunks of dead fish. It's all falling down in a slow gentle rain around you. There is one organism that likes it where you are. It's bacteria. Nasty little critters too small for the eye to see. These bacteria feed on all the debris but they don't produce a speck of oxygen. The water is cold, heavy..dense and dark. Up on the surface it's windy out today. The wind is ramping off your south road at about 30 knots, but you can't feel it. Just the dark and the cold. And absolutely NO oxygen.

Now picture yourself about four feet under the surface. The water is really warm, like a bathtub. Maybe 18 degrees warmer than down on the bottom! But plants are all around. Algae everwhere. Rooted plants, too. All producing oxygen. That wind is creating whitecaps above you. Oxygen is king. The water isn't as heavy either. It's lighter and less dense. It dances on top of the deeper, colder layer like a hot air balloons drift above the land.

Now, as fall arrives and the nights start to cool, the surface temperature starts to creep down. The differential that was once 18 degrees is 16, then it's 13, and ten and eight. Suddenly the warm water isn't dancing anymore. It's nearly as heavy as the water below. It's like your eleven-year-old son who wants a piggy back ride. He might just collapse on top of you!

Then something happens. It's cool and windy out, or there's a cool rain falling and that differential drops to about nothing and WHOOSH!!! the pony ride is over. Top and bottom mix, maybe in just a couple of hours. All of the crud and anoxic water is suddenly everywhere. Oxygen plummets, clarity plummets, and shoreline plants sometimes even starve for light and die.

Anywayssssss........What I'm saying is that it's not so much the differential that makes it turn over, it's the reduction and elimination of the differential. Your three degree difference, if following a couple of months of larger differentials could make you about to "flip". Once it does there will be a period of time where the temperature differential will virtually cease to exist. Now if you've been aerating all summer, then you've likely never had this big differential and you may not turn over at all.

We've talked about this before.

Lay off the gas, Man! Just lay off the gas.

Amazing...good post, better read. Thanks Bruce !

Bruce,

Even East Texans can understand that explaination! Thanks.

BTW, I was starting to shiver...

Gator

Inspiring, Bruce.

In my next life, I want to be a bacterium.

Bruce :

I was with you until the last sentence . How about this : Now if you've been aerating all summer , then you've likely already eliminated this big differential by aerating as you have been turning over a little at a time every day.

After all both aerating and fall turnover are both forms of water mixing , the first in a controlled manner the second by natural and uncontrolled means. Both add o2 to deeper water and bring nutrients to the surface . ewest

Double - Two main forces interact in a natural pond turnover - termperature difference and wind action. The greater the temperature difference between the layers the more energy it takes to mix the two layers together. Natural mixing is not just dependant on temperature difference between the layers. Stronger wind(larger waves) action will overcome greater temperature differences.

Bruce,

All I can say is Excellent Man !!!

Thanks for taking the time to sum it up like that. Do you have a literature background? I agree with some of the others.....WOW

Yes, Bruce really explained it well. I learned something. I used to think the Turnover Fairies did it.

I have a folder that I keep of really good posts. I've printed this one and will keep it. It is a great explanation about why too much aeration up North results in fish kills.

It brings about a thought/question/theory. In lieu of aeration, could a submersible pump with the outlet pointed toward the surface also help eliminate the differential and assist with aeration? I expect it would depend on factors like pump pressure or HP, depth of pond and pump placement, pond location (Yankee Land or Redneck Country), and other factors. It seems like it would work. If so, a pump in the upper 4 ft. of water pushing warmer, oxygenated water to the bottom should also effectively mix everything for a certain area. Since the warmer water would always be rising and the colder water always trying to drop, continued thermal circulation should occur. The only differential would be the loss of the oxygen bubbles.

It also brings about another question. I know the planktons can't survive their fall to the bottom. Can the bottom dwelling bacteria (the real pond cleanup crew) survive their trip to the surface?

Bruce -- did you hear Daryl Bauer's explanation? "What happens when a pond turns over? All the water runs out."

Sorry, couldn't resist. Great job on that description!

Bruce painted a great word picture of a thermal turnover.
Dave D's question...any kind of mixing helps. Pumping air is cheaper and more efficient than pumping water. Solarbee units lift water from the depths and push it in a circle to mix. Water pumps can lift "dead" water from deep and mix it at the surface, and vice versa.
When anaerobic bacteria hit the air, they're done. When aerobic bacteria lose oxygen sources, they're done. Nature seeks a balance, all the time. So, when we aerate, nature adjusts, in a good way...different bacteria, different oxygen levels, etc. More water becomes healthy, although we may need strategies to go from "bad" water to "good" water.

Hmmmm... aeration benefits aside, I have trouble imagining that air bubbles can circulate water as efficiently as direct water pumping. (watt for watt, of course.) Am I wrong? Probably so!

I had no idea there was a commercial solar powered circulation pump on the market. I was planning to build my own. There is no end to the things I have learned here over the years.

Thanks Bruce! Think I'll play it safe and just continue to areate, as like I posted a while back- I started with coffee brown water, beginning to get that summer stink, and now it is green, just right on clarity, and the fish are VERY active again at feeding time. Awesome explaination. Tnx again.

There's a lot less energy lifting water with air as air naturally rises through the water column vs. forcing it up (which is what you do when pumping). However there is a limit as to how high you can lift water with air above the natural water level, but sinces it's not necessary with diffusers it's irrelavant.