Organics in Ron's Tank Water Study

[Randy Holmes-Farley]

Some comments about Ron's tank water study results pertaining to organics:

Here's his results:

http://reefkeeping.com/issues/2002-02/rs/feature/index.htm

1. He doesn't test for organics explicitly, but perhaps we can infer something from some of his data. He does report TKN (Total Kjeldhal Nitrogen). That type of nitrogen is nitrogen in organics plus ammonia. Since he measured ammonia and it was low, TKN is essentially organic nitrogen.

In typical plankton, the Redfield ratio is about 1:16:106:138 (P:N:C:O; mole ratio). So nitrogen is about

16x14/(31 + 16 x 14 + 106 x 12 + 138 x 16) = 6% of the total

I'm ignoring other things, like hydrogen, which will change the values only slightly)

So the average TKN he reports (0.6 ppm) correesponds to about 10 ppm organics. The range is especially large, from about 0.5 ppm to about 22 ppm. Too bad there was no correlation between the samples and whether people used skimmers.

2. If the above calculation is roughly right, then the organic phosphorus values ought to be calculable too. P is about 1% of the total, or about 0.1 ppm organic phosphorus. Ron gets 0.3 ppm phosphorus (a very high value, IMO) and this 0.1 ppm could certainly be part of it.

 

[tatuvaaj]

So that we can get some idea about natural levels, here's what Sorokin gives for N and P:
N = NH4-N + Org. N
P = Org. P

Randy, please check my umol->mg/l conversion since I really don't know if I did it right. Those levels seem almost too low...

Is this the right way:
xE-6 * Atomic Weight * 1000 = x mg/l

Normal lagoon reef:
N 2.1-7.3 umol/l (0.029 - 0.102 mg/l)
P 0.15-0.25 umol/l (0.005 - 0.008 mg/l)

Lagoon of polluted reefs:
N 3.8-9.9 umol/l (0.053 - 0.139 mg/l)
P 0.37 umol/l (0.011 mg/l)

High latitude reefs
N 3.1-33.9 umol/l (0.043 - 0.475 mg/l)
P 0.14-1.6 umol/l (0.004 - 0.05 mg/l)

"Coral reef ecology", Y.I. Sorokin 1995

 

[SteveN]

I can't speak for any others, but I can say I was the sample in the red dot, which the way I understand the graphs from a quick reading last night is that I have the "mean" tank. I have readings of 0.037 mg/l NH4-N, 0.46 mg/l Total nitrogen (TKN), and 0,034 mg/l NO3 + NO2 nitrogen. I hope those numbers help. It seemed to me that they were "in line" with NSW values. If they are on the high side it is probably because I killed several new corals with temp about a week before the sample. I think he asked if tanks were skimmed or not. It probably will come into play in part 2-3. FWIW, my tank is unskimmed.

 

[Randy Holmes-Farley]

Tatu:

Randy, please check my umol->mg/l conversion since I really don't know if I did it right. Those levels seem almost too low

Your conversions look fine. What numbers seem low?

 

[Randy Holmes-Farley]

Steve:

and 0,034 mg/l NO3 + NO2 nitrogen.

Wow, not much nitrate in your tank (.

I wonder if the fact that the samples sat around for weeks in closed bottles has skewed the nitrogen and other nutrient numbers.

 

[tatuvaaj]

Your conversions look fine. What numbers seem low?

It was so late at night (here in Finland) that I couldn't think (or type) very clearly

What I meant was that there is quite a lot TKN in tanks tested compared to even polluted reefs (0.6 mg/l vs. 0.139 mg/l). I would have thought that average reef tank would have had much less organics, maybe around 2x NSW levels. Now it seems that the levels are more like 5x for N and 15x for organic P!

BTW, do you know if the samples were filtered in anyway? If not, wouldn't POM contribute to these values?

 

[Randy Holmes-Farley]

Tatu:

What I meant was that there is quite a lot TKN in tanks tested compared to even polluted reefs (0.6 mg/l vs. 0.139 mg/l).

I agree that they are high. It doesn't surprise me that much considering how many organisms we have in a small water volume.

BTW, do you know if the samples were filtered in anyway? If not, wouldn't POM contribute to these values?

I don't know if they were filtered, and yes it would contribute. Do you know if the Sorokin numbers reflect filtration?

 

[tatuvaaj]

I don't know if they were filtered, and yes it would contribute. Do you know if the Sorokin numbers reflect filtration?

No I don't. The table that contains that data is labeled as "Level of ambient concentrations of dissolved organic and inorganic nutrients in..." Since he specifies dissolved, wouldn't that mean that samples should have been filtered by a filter with a nominal pore size of about 0.5 um? (This is the definition I have for DOC).

 

[Randy Holmes-Farley]

Tatu:

I agree that those were probably filtered. I posted a question to Ron in the magazine forum to find out if his were.

 

[Randy Holmes-Farley]

Tatu:

As you've probably seen, Ron is asking if the water was filtered.

 

[tatuvaaj]

Yes, I saw your thread, thanks!

The thread can be found here: http://www.reefcentral.com/vbulletin/showthread.php?s=&threadid=62000 if anyone else is interested.

 

[Randy Holmes-Farley]

For anyone who has not seen Ron's answer, he said they did not filter the water. Consequently, it contains particulate organic matter (POM) as well as dissolved organic matter (DOM).

 

[SteveN]

It seems to me that this is a more accurate result of the Nitrogen that is actually in the tank. Or is the concern that there was some that was stirred up and others that didn't have the POM thus skewing the results?

 

[Randy Holmes-Farley]

You are right that it is a better measure of the total nitrogen around. I doubt anyone stirred suff up before taking a sample, but I don't really know.

OTOH, if one is comparing seawater to tank water, we'd need to have equivalent tests, and the one that was described above for seawater eliminated the POM. The POM seems to vary a lot from place to place as board members that dive say it is sometimes cloudy with plankton, and sometimes very clear.

It would be nice to compare tanks to seawater for both POM and DOM, but I guess we can't expect to stretch Ron's test results too far.

 

[NanoCube-boy]

intersesting.