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#835124 - 07/23/08 08:35 PM Oxygen content
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10 Point


Registered: 09/28/03
Posts: 2638
Loc: Lebanon

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I posted a question on another fishing forum about O2 content, asking about the effects shallow water may have on it.

Several mentioned how the thermocline is more important to consider than the depth. But it seems like I remember someone on here writing about Priest not going through this change...or maybe it was during a different season.

Can anyone shed some light here? I can't catch numbers lately in shallow or deep water, day or night lately. It's about that time to hang up the polls and start shootin the bow more, but I'd still like to get a few more weeks in.

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#835376 - 07/24/08 12:49 AM Re: Oxygen content [Re: Back Home]
bowriter
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Registered: 08/31/02
Posts: 42220
Loc: Lebanon,TN USA

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All I know is Priest turns over just as any other lake does.
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#835496 - 07/24/08 06:05 AM Re: Oxygen content [Re: bowriter]
trealtree
16 Point


Registered: 09/29/04
Posts: 10824
Loc: Middle Tennessee

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I think rivers are the only thing that dont turn over.
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#836375 - 07/24/08 03:20 PM Re: Oxygen content [Re: trealtree]
B.D.
8 Point


Registered: 03/24/08
Posts: 1484
Loc: Hendersonville TN

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"Turnover" happens because of a weird physical property of water. Like most substances, water gets more dense as it gets colder. BUT water reaches maximum density at 39 deg. F, and then - unlike most other substances on the planet - it starts to become less dense again.

Thus, in warmer months, most big lakes without a lot of current will stratify, with warm water at the surface and cooler, denser water beneath. This happens on Priest, Center Hill, Dale Hollow, and most other reservoirs.

There is an exception: "run of the river" reservoirs like Old Hickory, Cordell Hull, Cheatham, etc. reservoirs don't experience a turnover because they have current. This mixes the water and prevents it from stratifying.

In the fall, temps drop, and the surface water gets cooler and cooler, until it gets into the low 40s. At that point, there's very little difference in density between the water at the surface and water down below, and it mixes. This is "fall turnover."

If the temps continue to drop, the water at the surface will get less dense, and the lake will re-stratify with water colder than 39 F at the surface and warmer water down below. When surface temps warm up to 39 or 40 in the spring, it re-mixes and "sprign turnover" occurs.

We only get a fall turnover in Middle Tennessee. Our lakes typically don't get cold enough for long enough in the winter to re-stratify so that a spring turnover can occur.

How does this tie in with oxygen? Well, water absorbs oxygen from the air. However, when a lake stratifies, the water down deep doesn't get contact with the air, so it can't get new oxygen. Over time, the oxygen in the water gets depleted. In a fertile lake, dissolved oxygen can get entirely depleted in the depths.

Many fish prefer cooler water in the very hot part of the summer. Normally, they'd go deep, below the thermocline into the stratified, cooler water. However, if that water has run out of oxygen, they may be forced to stay shallow. If the water at the surface gets too hot and the deep water doesn't have any oxygen, you can get a fish kill. This actually happened to the stripers on Cherokee from time to time before they installed oxygen infusors and created the "no fishing zone" in the summer above the dam.

bd

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#836823 - 07/24/08 09:03 PM Re: Oxygen content [Re: B.D.]
gil1
12 Point


Registered: 04/06/07
Posts: 6349
Loc: Nashville, TN

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Dayum son, I knew the very basics of all that, but I've never read it explained in an easier way. I think my little brain just wrapped right around that whole concept. Bless you, sir.
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#836827 - 07/24/08 09:06 PM Re: Oxygen content [Re: gil1]
MFBAB
10 Point


Registered: 01/08/08
Posts: 2997
Loc: Memphis, TN

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Good answer!
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#836993 - 07/25/08 05:05 AM Re: Oxygen content [Re: MFBAB]
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10 Point


Registered: 09/28/03
Posts: 2638
Loc: Lebanon

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Impressive! Now, if you can just make it that simple for me to catch more fish. Let me know when you have those answers. \:D
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#837394 - 07/25/08 09:28 AM Re: Oxygen content [Re: Back Home]
Jason Eldridge
10 Point


Registered: 05/31/04
Posts: 3422
Loc: South Carolina

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Interesting stuff
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#839022 - 07/26/08 02:35 PM Re: Oxygen content [Re: Jason Eldridge]
Crosshairy
10 Point


Registered: 08/22/06
Posts: 2695
Loc: Bartlett, TN

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One more piece of info for you - a lot of oxygen deficiency in hot months is driven by a thermodynamic principle called the "Kinetic Gas Law".

It's really simple - hot gases have more energy than cold gases. Pretty much everyone can figure that part out. The way it applies to whatever, however, involves the question of oxygen solubility.

The solubility of oxygen in water goes down as the temperature goes up - this is explained because the air dissolved in the water gets more energy, so it can't stay in solution. It's sort of like giving more and more caffeine to a bunch of kids and telling them "don't move!"

That's why colder rivers hold trout (more dissolved oxygen) than warmer ones do. All the rocks and boulders stirring things up helps too :).
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