Whats the best way to determine DOC (dissolved organic compounds)?

[Dana Riddle]

Other than skimming, UV light and ozone also reduce the yellow-ness of water, but I wonder if the oxidation and UV only modify the structure of the organic molecules that absorb light, OR do they actually change the availability of dissolved organic material for organisms to consume.
In other words, do they make the water cleaner (lower in organic nutrients) or just clearer (less yellow)?

Bruce Carlson published a paper in the late 90's on various tanks at the Waikiki. The 'office' tank used ozone and it was 'clean' (my word, not his. I'll try to find that paper.

 

[taricha]

I wanted to circle back to this question...

UV light and ozone also reduce the yellow-ness of water, but I wonder if the oxidation and UV only modify the structure of the organic molecules that absorb light, OR do they actually change the availability of dissolved organic material for organisms to consume.
In other words, do they make the water cleaner (lower in organic nutrients) or just clearer (less yellow)?

Bruce Carlson published a paper in the late 90's on various tanks at the Waikiki. The 'office' tank used ozone and it was 'clean' (my word, not his.

I ran across this while thinking about something else, that seems to address it directly.
From Marine Photochemistry and its impact on Carbon cycling

To unpack this a little bit. DOM = dissolved organic matter. Elsewhere it clarifies that matter it's discussing here is specifically the yellowing substances in marine water, and that this can be photo-degraded by light in the UV/Violet/Blue. This photo-degradation happens in part due to reactive species like hydroxyl and other oxidizers that are formed when this light is absorbed by the DOM.
So it's quite possible that UV or oxidizers in our systems are turning yellow refractory (hard to use) oganics into labile (easily consumed) carbon sources.

 

[Dan_P]

I wanted to circle back to this question...



I ran across this while thinking about something else, that seems to address it directly.
From Marine Photochemistry and its impact on Carbon cycling

To unpack this a little bit. DOM = dissolved organic matter. Elsewhere it clarifies that matter it's discussing here is specifically the yellowing substances in marine water, and that this can be photo-degraded by light in the UV/Violet/Blue. This photo-degradation happens in part due to reactive species like hydroxyl and other oxidizers that are formed when this light is absorbed by the DOM.
So it's quite possible that UV or oxidizers in our systems are turning yellow refractory (hard to use) oganics into labile (easily consumed) carbon sources.

Nice find. I see you are using your free time wisely

Ozone also breaks up big molecules. At one time ozone in a skimmer was a “thing” because it was thought that these smaller molecules were more likely to be removed by the skimmer. I think @Randy Holmes-Farley will have this in his memory banks, might even be in one of his articles.

 

[taricha]

Nice find. I see you are using your free time wisely

Hah. I'm trying to catch up a bit on my reading list. Since the baby joined us in June, I've been doing night duty. Doing experiments works fine, but any time I would sit down to read something, I fall asleep in 5 minutes.

 

[Randy Holmes-Farley]

Ozone certainly can make refractory molecules more bioavailable (and certainly less light absorbing), but it does not necessarily reduce concentrations.

Here's a section from one of my ozone articles:

http://reefkeeping.com/issues/2006-03/rhf/index.php#10

In a marine mammal pool,18 for example, it was found that disinfection with 4 ppm ozone with a 30 minute contact time (a disinfection level much higher than is typically used in reef aquaria) did not reduce the pool's total organic carbon (TOC) (~13 ppm TOC), while the use of granular activated carbon (GAC) did reduce it by 37%. Interestingly, the combination of ozone and GAC was even more effective, removing 60-78% of the TOC, suggesting that the ozonation may have altered some of the molecules in a way that made them bind more strongly (or more rapidly) to GAC. An alternative explanation that cannot be ruled out involves biological transformations of the organic compounds taking place on the GAC surface as it became colonized with bacteria).

This is the reference cited:

18. Effects of tertiary methods on total organic carbon removal in saline, closed-system marine mammal pools. Adams G; Spotte S. American journal of veterinary research (1980), 41(9), 1470-4.