One point to consider is that the data was collected from a system containing ~10 oz of fish (!) in 15 gallons of water. Does similar chemistry happen in more dilute systems like a reef aquarium?
May be a useful tool. BOD 3 for fast DOC and BOD7 for fast DOC+ POC
A second point to consider about the data from this system is the DOC accumulation is in the neighborhood of 10-30x amount accumulated in the reef aquarium water (NDOC data posted to this forum). At the higher concentration, would there be different chemistry occurring and different molecular weight distributions and digestibility?
Yep. My system generates fine particulates of calcium carbonate, and this seems evenly mixed with organic debris. You can sample this fine dust-like material and dissolve the large majority of it in acid, but some brown debris will remain after acid dissolution.
True. Is there a corollary to the mantra "the concentration makes the poison" that goes instead "the concentration makes the food"? Because that seems often relevant. Some things that nobody wants to eat in extremely small concentrations look more like a food if the concentration gets a lot higher.
Nice work and clear presentation. There is a publication in your future that ties your studies together.technique: Fluorescence of water
Within the total DOM, there is a subset of DOM that has some color (or UV absorbance) this is sometimes called chromophoric dissolved organic material (CDOM), and within that subset of chromophoric dissolved organic material - some of that material that absorbs light also fluoresces (FDOM) with part of that fluorescence happening in the visible.
This ends up being observable as a blue-green glow in tank water for most anyone who shines a 365nm UV flashlight into their tank.
Here's some examples from the forum:
https://www.reef2reef.com/threads/u...-in-shorter-wavelengths.1011643/post-11817521
https://www.reef2reef.com/threads/is-390nm-400nm-light-useless.1029598/post-12109358
https://www.reef2reef.com/threads/official-euphyllia-show-off-thread.29432/post-12642256
Here's an illustration of what a sample of tank water with a small amount of fish flake turns into with UV 365nm excitation...
(note that 365nm uv passes distilled water with no effect, but organic-laden sample - even after filtering - fluoresces brightly)
I've also used it to measure (filtered) aquarium water and bacterial samples after digesting some fish flakes. The fish flake water itself has nearly none. So it represents a breakdown product of organics.
These were the filtered sample waters after a few different bacterial products digested fish flake for a while. Generally more active samples had higher fluorescent emission - but my aquarium water was far higher than all the samples - indicating some amount of accumulation over time.
In order to quantify this, you need a spectrometer and a UV365nm source - I use a flashlight off of amazon I shine it vertically down into the cuvette (glass - plastic is too fluorescent on its own) and measure the fluorescent emission in the spectrometer.
So what is being measured here?
in papers on marine FDOM - they often use excitation-emission-matrixes to chart what is observed about the absorptions and emissions and then statistically decompose these into different components which they attempt to assign to chemical groups.
The red dashed line shows the portion of the EEM that using a 365nm light can fluoresce visibly.
Usually these regions of the EEM are assigned to "humic-like":
It's interesting that it usually is associated with terrestrial sources but can be found widely in the open ocean.
"Factor Analysis (PARAFAC) of fluorescence spectra revealed that coastal and oceanic dissolved organic matter (DOM) fluorescence could be separated into at least eight separate components: 4-5 humic-like and 3-5 protein-like signals. Two of the humic components were identified as representing terrestrial organic matter and their signals could be traced in the open ocean (Pacific and Atlantic) at levels of approximately 1.5% of riverine concentrations. An additional humic component, traditionally identified as the “marine” or “M” peak, was found to be both sourced from land and produced in the ocean."
Distinguishing between terrestrial and autochthonous organic matter sources
in marine environments using fluorescence spectroscopy
Although this is a subset of the "yellow" compounds, in some ways it's easier to measure than trying to quantify visible yellow-ness - because you can simply blast a 1cm cuvette of tank water with strong enough UV-365nm light to generate a small amount of measurable visible light emission in the 430nm region.
Is it important? probably not moreso than the general humic-like yellow stuff in our water. Some of it is a little digestible, but mostly it's a recalcitrant waste product. I view it mostly a more sensitive way to quantify yellow-ness in water.
I find the two I have marked with blue most interesting
Sincerely Lasse
Had to look up some stuff to understand the question (amino acids with the wrong handed-ness are much less digestible, and bacteria make those sometimes).
Agreed - this analysis works. It gives me fairly sensible results as well. Just don't leave notable airspace in the container or else the calculation of CO2 partitioned between airspace and water gets much harder.
Good Q.
Here’s another question
In my fuzzy chemistry way of thinking, some of the vinegar gets oxidized for energy. So the O2 combines with the Carbon from vinegar to change one weak acid (vinegar) into another (CO2). So maybe not that much of a pH change.
agreed, but without reliable measurement methods - what counts as "good husbandry" is mostly guesswork and anecdote.
Reefers didn’t have the data we have now, but they could communicate what “good husbandry” was/is.In my fuzzy chemistry way of thinking, some of the vinegar gets oxidized for energy. So the O2 combines with the Carbon from vinegar to change one weak acid (vinegar) into another (CO2). So maybe not that much of a pH change.
I'm aware this fuzziness skips too many steps to be a useful analysis of what will actually happen.
agreed, but without reliable measurement methods - what counts as "good husbandry" is mostly guesswork and anecdote.
Your list is a good one, but measurements can tell you which of those are more effective than others. From what I've seen 2,4,5 are pretty effective and 3 (and maybe 1) perhaps not so much.
For the pH measurement did you fill the cuvette entirely and add an extra drop of reagent? Or just accept the error of the little bit of air in the cuvette when using 10ml sample?
