Can Aeration Change the Equilibrium of Gases in Water?

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Discussion Overview

The discussion revolves around the effects of aeration on the equilibrium of gases in water, particularly in the context of photosynthesis by live plants. Participants explore how the introduction of atmospheric air into water might influence the dissolved levels of oxygen (O2) and carbon dioxide (CO2) during the day when photosynthesis occurs.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant posits that adding live plants will skew the ratio of O2 to CO2 in the water towards O2 due to photosynthesis.
  • Another participant suggests that the final effect of aeration on gas ratios will depend on the kinetics of gas production and exchange.
  • A question is raised about whether increased aeration would push the gas ratio back towards equilibrium by enhancing the air/water interface.
  • It is proposed that once the speed of gas exchange is sufficiently high, the presence of plants or animals becomes irrelevant, and the composition of dissolved gases will align with atmospheric levels.
  • One participant agrees that once equilibrium is reached, further aeration will not alter that equilibrium.

Areas of Agreement / Disagreement

Participants express differing views on the impact of aeration on gas ratios, with some suggesting that aeration will increase CO2 levels while others argue that equilibrium will ultimately prevail regardless of aeration levels. The discussion remains unresolved regarding the exact dynamics of gas exchange in the presence of photosynthesis.

Contextual Notes

Limitations include assumptions about the rates of gas exchange and production, as well as the specific conditions under which equilibrium is defined. The discussion does not resolve how these factors interact in practice.

Subrosa
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Hi, first time poster. Here's the scenario. In a given vessel containing a given amount of water at a given temp, gases from the air will reach equilibrium with those dissolved in the water contained in the vessel. Now suppose live plants are added to the water. During the day, photosynthesis will occur, which will skew the relative ratio of O2 and CO2 in the water towards the O2. If while this is occurring, atmospheric air is diffused into the water via an airstone powered by an air pump, what will be the effect on the ratio of CO2 to O2? It seems obvious to me that under these circumstances that aerating the water will increase the level of CO2 dissolved in it, however marginally. Is this correct? Thanks!
 
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Yes, but the exact final effect will depends on kinetics - how fast gases are produced and how fast gases are exchanged.
 
Thanks for the quick reply!
 
Ok one more question. All else being equal, wouldn't increasing levels of aeration push the ratio more strongly back towards equilibrium (in this case higher CO2 levels)through increasing the surface area of the air/water interface?
 
Once the speed of exchange is high enough, presence of plants/animals stops to matter, and the composition of dissolved gases is always the same (and in a simple equilibrium with those present in the atmosphere).
 
My thoughts exactly sir. The water and air "want" to be at equilibrium with each other, and once equilibrium is reached no amount of air pumped through the water will change that equilibrium. Thank you again!
 

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