Re: Aquatic Plants Digest V2 #832

["Roger S. Miller" <rgrmill at rt66_com>]

> >Date: Sun, 13 Jul 1997 18:12:23 -0400
> >To: aquatic-plants at actwin_com
> >From: Sanjay Joshi <sjoshi at psu_edu>
> >Subject: CO2-Kh-PH table: Reference Wanted
> >
> >I have seen the CO2-Kh-pH tables in several places. I am looking for
> >a published reference that explains the chemistry behind these
> >tables, and also provides the formulas and equations used to derive
> >the tables.
> >
> >Thanks,
> >
> >sanjay joshi

There are probably any number of references for the tables, as they are
based on rather basic aqueous chemistry.  My fav is

Skougstad, M. J. et al, 1979.  Methods for determination of inorganic
	substances in water and fluvial sediments.  Techniques of
	Water-Resources Investigations of the United States Geological
 	Survey, Chapter A1. U.S Government Printing Office, Washington,
	DC. 626pp.

I believe there is a newer version of the same reference.

The formula (on page 280) is rather simple:

	mg/L CO2 = 1.60 X 10^(6.0-pH) X mg/L HCO3-

Note that HCO3- in mg/L is alkalinity in German degrees kH * 21.8.

The formula is good for fresh water with less than 800 mg/l of solutes.
Sea water will depart significantly from this relationship because of
variations in activity coefficients and the importance of several
complexes (CaHCO+, and so on) that form in concentrated solutions.  It may
be possible to use programs like USGS' PHREEQC code to  produce a
similar, semi-empirical relationship for sea water.


Roger Miller

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