Water analysis 'not detected'

[simonh]

Hi Ron,

First let me thank you for all the work put into this study and enormous amount of time it must have taken compiling your first article.

On your analysis I noticed some of the elements measured were 'Not detected'. I presume this means that they were below the detection limits of the analysis.

Do you have the detection limits for those analyses? I was interested in Iron for example. On these is the detection limit below the NSW concentration (i.e. the 'true value' must therefore be below the NSW levels, so we could classify them as 'less than' relative NSW) or is the detection limit above the NSW levels (i.e we classify these element as 'not known' relative to NSW)?

Hope my question makes sense.

 

[Randy Holmes-Farley]

Simon:

The detection limits should absolutely be given. This is most critical for elements where the detection limit is actually HIGHER than surface NSW levels (like iron). For these ions, the tank levels may still be above NSW levels, but be below detectable limits.

 

[cvye]

another control group

another control group

Excellent study!
However, I would have added an additional control group (given that the majority of subjects used Instant Ocean as a salt mix):

IOSW - say a vat of Instant Ocean based seawater, perhaps aerated for 48 hrs and re-adjusted for salinity using RO/DI.

Be that as it may, the conclusion that our tanks are not even close to natural seawater is an old one, I believe, credited to Steve Spotte?

What will be much more interesting will by your future article(s) describing the tanks with "problems" and those without and which ones those were in the spectrum! Can't wait!

 

[rshimek]

Hi,

All of the detection limits will be given in the next article.

For iron the D. L. was 0.005 mg/l

My table lists NSW sea water as 0.02 to 0.002 mg/l

cvye,

The IO values in the study DO come from a sample of IO made up as described in the materials and methods.

 

[cvye]

oops, dopey me, I missed that which is so clear on re-reading.

 

[tatuvaaj]

Dr. Shimek,

First let me thank you for your great work! These types of study can really benefit hobbyists!

Comments:

Your data for NSW levels seem to be quite different from tables I have (for example see this excellent page with references: http://www.dnai.com/~patwilde/ocpertbl.html)

Was your data compiled from reef waters or was there any other reason to select that study as a reference?

The data from 1966 seems quite old. In the book "An introduction to the chemistry of the sea" by Michael E. Q. Pilson he states that no data published about trace elements before mid 70s should be trusted. The link I provided seems to have more recent data for example for Fe (4.50E-05 ppm).

Once again, thank you very much for the hard work you have done!

 

[Randy Holmes-Farley]

Surface water iron values (in the top 50 meters) are much lower than the water column overall due to sequestration by growing organisms. Values can be equal to 0.1 nM (0.000006 ppm).

 

[Randy Holmes-Farley]

Tatu:

Oops, I guess we posted the same thing at the same time.

 

[tatuvaaj]

Randy,



Do you agree with Pilson about trace metal measurements before say 80s being unreliable?

 

[rshimek]

Hi Guys,

[thanks]

Tatu,

I will be glad to use the link you provided to get more up-to-date data for the subseqent articles about these data.

The data I used simply came from a reference on hand, and were originally from Svedrup's oceanography text.

Randy,

If you have any other suggestions for obtaining up-to-date data online, I could certainly use them.

 

[tatuvaaj]

Even the data in that web page is old when compared to the Pilson's book I mentioned earlier - he has compiled data for trace elements from several studies mainly from the 90s. So if you happen to have access to that book it might be a good source.

I just compared the data in Pilson's book to the "An introduction to marine biochemistry" by Susan M. Liebes (as you can see, I'm at the "An introduction..." level ) and they seemed to be reasonable close to each other. Liebes' data comes from "Chemical Oceanography", vol. 8, K. W. Bruland 1983 pp. 172-173

 

[Randy Holmes-Farley]

Tatu:

Your comment about old studies could certainly be true. Both collection and analysis techniques are much better now.

One concern that I have about using any single number is that for many of these ions there is a profile that changes greatly with depth. Sometimes the difference is several orders of magnitude. I'm not sure how to deal with that in this context, except to try to compare to surface water values.

Ron:

Unfortunately, I don't know of any good online tables. Millero's book "Chemical Oceonography" (1996) is pretty good with tables and graphs of data.

 

[rshimek]

Hi Randy,

I was afraid you were going to say that.

Since my initial forays into chem-ocean classes thirty years ago, I have avoided purchasing new text... and I surely can't get my hands on a copy of one at the local University (know to one and all as, Moo -U (or mebbe moo-ewe).

I share your concerns with comparing to NSW, actually, and the thrust of this study is not that comparsion, but rather a comparison within reef tanks, and I hope to use natural data sparingly unless there are very great differences.

Additionally, surface mid-ocean waters are likely to be very different from reef waters, and reef data are damnably hard to come by.

 

[tatuvaaj]

I don't know the rules about posting scientific data so I hope they don't lock me in the jail...

Edited:
Oops, I guess you people are not using UNIX so the attachment isn't very clear
Here is the data:
<pre>
Mean Range Distribution
Li 25 umol - C
Be 20 pmol 4-30 N;Sc
N 30 umol 0.1-45 N
Al 10 nmol <0.1-40 Mm
Si 100 umol <1-200 N
P 2.3 umol <0.1-3.5 N
Sc 15 pmol 8-20 Sd
Ti 200 pmol 4-300 Sd
V 30 nmol 20-35 Sd
Cr 4 nmol 2-5 N
Mn 0.5 nmol 0.2-3 Dd
Fe 1 nmol 0.1-2.5 Sd;Dd
Co 20 pmol 10-100 Sd;Dd
Ni 8 nmol 2-12 N
Cu 4 nmol 0.5-6 N;Sc
Zn 6 nmol 0.05-9 N
Ga 20 pmol 2-50 Cx;Sc
Ge 70 pmol <7-115 N
As 23 nmol 15-25 N
Se 1.7 nmol 0.5-2.3 N
Rb 1.4 umol - C
Y 250 pmol 80-300 ?
Zr 200 pmol 12-300 N;Sc
Mo 100 nmol 92-105 C
Rh 0.8 pmol 0.3-1.0 Sc; N?
Pd 0.6 pmol 0.2-0.6 Sd
Ag 25 pmol 0.5-45 N; Cx
Cd 0.7 nmol 0.001-1.1 N
Sn 4 pmol 1-12 Dd?
Sb 1.2 nmol ? ?
Te 0.6 pmol 0.4-1.7 Sc
I 0.4 umol 0.2-0.5 N
Cs 2.2 nmol - C
Ba 100 nmol 32-150 N
La 30 pmol 8-57 Sd

Ce 20 pmol 16-26 Sd
Pr 5 pmol 1-8 Sd
Nd 25 pmol 5-40 Sd
Sm 4 pmol 1-6 Sd
Eu 1 pmol 0.3-1.7 Sd
Gd 6 pmol 2-9 Sd
Tb 1 pmol 0.2-1.5 Sd
Ho 2.5 pmol 0.5-3 Sd
Er 8 pmol 2-10 Sd
Tm 1 pmol 0.3-1.5 Sd
Yb 7 pmol 1.5-11 Sd
Lu 1 pmol 0.2-1.8 Sd
Hf 20 pmol ? Sd
W 56 pmol 45-67 C
Re 40 pmol - C
Pt 1 pmol 0.54-1.64 Sd
Au 50 fmol 20-200 variable
Hg 2 pmol 0.5-12 Cx;Sc
Tl 60 pmol - C
Pb 10 pmol 5-175 High in surface water
Bi 0.1 pmol <0.015-0.24 Dd
U 13.6 nmol +- 1.2% C

All values units per kg.
C = Conservative
N = Nutrient
Sd = Surface depletion
Dd = Depletion at depth
Mm = Mid-depth minima
Sc = Scavenged
Cx = Complex

From "An introduction to the chemistry of the sea", Michael E. Q. Pilson 1998
</pre>

 

[rshimek]

Hi Tatu,

<b><font color="deeppink">THANKS!!!</b></font>

I truly appreciate it. There is no problem posting any data as long as they are appropriately cited or referenced.

 

[Randy Holmes-Farley]

Tatu:

That table has almost exactly the same data as the table that I have.

 

[rshimek]

Hi Randy,

Okay - I will work with these data in the downstream comparisons with trace elements.

 

[simonh]

Thanks guys.

It was the last figure in your article which I found very useful for seeing which elements were higher / lower than NSW. It was just slightly confusing that the 'not detected' items were relabled as absent with small bars well below NSW. IMO it would have been nice to draw these bars from 0 upto the detection limit expressed relative to NSW. Maybe that was not done because these would be very high relative concentrations for some of the trace elements?

 

[rshimek]

Hi Simon,

I may try a graphic like you describe, but it is a bit dicey in construction - as detection limits vary over couple orders of magnitude; it maybe easier to do it with a table.

The main problem here is "pitching to the audience." While people like yourself, Randy and Tatu have no trouble working with a log-scaled graph, I think (based on the talks I have given) that a lot of folks do. If I could have figured out a way to present the data I did differently - and concisely - I would have.

And I should have use ND or some such abbreviation instead of "Absent" - but just didn't flash on it at the time.

 

[Mutagen]

Ron,

A short while back the possibility of posting specific research papers pertinent to the hobby was raised. At that time, you suggested there may be copyright infringement problems and/or costs associated with that idea. However, you indicate posting data is OK as long as it is appropriately cited or referenced. I'm not saying that both statements can't be true, but I am curious as to where one draws the line. What are your thoughts on this?

Thanks for your time, Tracy Gray