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Piper plot alkalinity confusion


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I'm stuck on how to use Bicarbonate in GSS and making a Piper plot. My lab data comes in the typical form of:

 

Bicarbonate (as CaCO3) mg/L

Carbonate (as CaCO3) mg/L

 

But there are no instructions on how to use the lab data in GSS. Firstly, there is no analyte called "Bicarbonate" so I assume I add it as a User define analyte, choosing mg/L as CaCO3 in the units column? Does this mean GSS/Gtplot will automatically calculate it as HCO3 (eg. divide by 50.04 (mg/meq))?

 

Carbonate is more straight forward as it populates as Carbonate Alkalinity mg/L as CaCO3. Easy copy/paste from lab data into GSS. But does it also undergo a conversion to CO3?

 

It would be really handy to see a GSS screenshot of the analytes/parameters list needed for a Piper plot. The video tutorial is not helpful in this regard as the complete list is not shown :(

 

Thanks,

Marie

 

 

 

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Hi Marie,

 

There are two ways to do this. The first is to simply set a value for the HCO3- basis entry. The HCO3- entry will already be included when you open a new GSS spreadsheet, but if you delete it, just click the "+ analyte" button at the bottom of GSS, then choose Basis species -> HCO3-. Then you set the bulk concentration of the HCO3- component. In other words, it is the sum of CO2, HCO3-, CO3--, NaHCO3, etc, not just the free HCO3- species. This is the same way you typically define the majority of basis entries in a calculation. What you enter for HPO4--, as another example, is a bulk constraint equal to the sum of H2PO4-, HPO4--, PO4---, etc. species. You can choose from a variety of units to suit your analyses.

 

The HCO3- basis entry is a special case in that you can alternatively set the carbonate alkalinity. The carbonate alkalinity refers to the sum of the concentrations in solution of the free HCO3- and CO3-- species. To specify this value, click "+ analyte" -> Chemical parameters -> Carbonate alkalinity. If your lab results list the bicarbonate and carbonate contributions to carbonate alkalinity separately, and both of them are mg/l as CaCO3, just add them together and enter that total for the carbonate alkalinity. You cannot, of course, simply add the concentrations of free species in mg/l units because each species has a different mole weight.

 

Hope this helps,

 

Brian Farrell

Aqueous Solutions LLC

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