Note that the concentration for dissolved oxygen necessary for fish is only 5-10 mg/L. So a methane concentration of 26 to 32 mg/L is quite high enough to be “significantly biologically effective”.
Let’s say you’re right:
(1) fish need 5 PPM of dissolved O2 (in round numbers) to live in relatively warm waters. Agreed. That does coincidently equate to your figure of about 5 mg/L. Deep ocean species need less, warm water fishes might need more. But we can go with the 5 mg/L figure. Apples and oranges. What’s your point? You have merely pointed out that methane CAN be a solute at higher concentrations than the minimum O2 levels required to support aquatic life. Relevance?
BUT...
(2) Methane is NOT toxic, nor is it suffocating as a solute in water. The mere presence of dissolved methane is NOT a problem. Please cite a reference for how methane directly harms fish. I don’t even know what “quite high enough” or “significantly biologically effective” means or why it is in quotes in your post. Again, demonstrate in fact that ANY concentration of dissolved methane (up to amounts encountered in the Gulf) is a PROBLEM. Being smug— (on my part) the concentration of H2O is highest of all! ... and that’s not a problem.
What is it you want me to agree to that I have not yet acceded to?
Again, my point on this post/thread is twofold—
(1) Methane, according to my sources is, expressed in moles per litre, among the least soluble atmospheric and/or aquatic/marine natural gases. and (2) I have yet to see how the mere presence of higher-than-normal levels of dissolved methane is a PROBLEM in the marine ecosystem because it is NON-toxic.
As an aside, you’ll note I prefer to employ a solubility number expressed in moles (micro moles actually) per litre, because comparing solubility by mass (mg) can be misleading due to the difference in molecular weight of 02 versus CH4.
Now I’ll move to your next post.