Atmospheric Pressure Effects on Oxygen Levels

[StringJunky]

Why does low atmospheric pressure cause the oxygen leels in a body of water, like a lake, to rise....or so I am lead to believe?

 

I am an avid angler and it is a commonly held belief that, during low pressure, the oxygen levels rise and push the thermocline down causing fish to seek the bottom of the lake.

 

Does anybody understand the physics or chemistry of this phenomenon.

 

My instinct says that oxygen levels should rise with rising pressure since the atmosphere is 'pushing' more on the water's surface,.but apparently not

[Mokele]

Dissolved oxygen is higher at low altitudes because of higher atmospheric pressure, so you're right.

 

However, rising oxygen levels would allow fish to explore more of the lake, including areas like the bottom which are nutrient rich but usually lower oxygen than the surface.

[insane_alien]

if the pressure is low then that likely means the weather is a bit stormy, or at least windy.

 

this disturbance can cause mixing through the thermocline allowing for oxygenation of the bottom layers.

[StringJunky]

Thanks for your response IA

 

So you don't think it's down to a shift (somehow) in the concentration difference between the o2 in the atmosphere and that o2 already dissolved in the water when the pressure changes...I suppose like a concentration gradient.?

 

Your answer does make sense...I didn't think of it being a purely mechanical process, the wind and rain acting as a mixer!!

 

Going fishing now for two days ...will pick up on any more responses when I get back.

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Consecutive posts merged

Dissolved oxygen is higher at low altitudes because of higher atmospheric pressure, so you're right.

 

However, rising oxygen levels would allow fish to explore more of the lake, including areas like the bottom which are nutrient rich but usually lower oxygen than the surface.

 

Nearly missed sight of your post Mokele! Thanks

 

Will chew on it when I get back.

 

Cheers

[Theophrastus]

In terms of oxygen levels, there is a contrary tendency, in that oxygen solubility, in water, increases, with declining temperature, and as such, you could alternatively expect, more dissolved oxygen in cooler, possibly deeper waters, depending on the conditions, and factors at hand.

[insane_alien]

you don't tend to get oxygenation in deeper waters due to biological activity and limits of diffusion of oxygen through the thermocline.

[StringJunky]

have read tIhat article you linked to Mokele, thanks...It does support my hunch and explains a few other things like accounting for low oxygen levels at depth due to decomposition.

 

IA: The depth of my lake averages 12ft and, apparently, thermoclines do not occur at this depth or less: surface water temperatures generally don't go over 21oC in summer- measured at night.

 

http://www.lakeforktexas.com/Pages/therm.html

 

Is the depth of my lake shallow enough for atmospheric oxygen diffusion to occur down to the bottom of the lake without mechanical agitation from wind and rain?

 

In periods of low pressure, even during calm weather, fishing and fish (carp) activity on the bottom is usually brisk. Oxygen levels, on average ( I suspect), should be lower and penetrate less to the depths during these periods than those of high pressure and brisk weather activity, water temperature staying the same. The presence of aquatic weed is low in the lake.

 

Any thoughts or links that might explain this apparent anomaly would be appreciated.

 

Sometimes, I find it difficult to think of the right keywords to Google to answer my own questions!

Edited August 7, 2009 by StringJunky
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