Usage of "alkalinity" definition in Solution block

[ANar]

Hi everyone,

Does anyone could explain how PHREEQC is treating the definition of carbon as "alkalinity" in the solution block?
I am working with saline water composition and sit.dat database, and have carbon concentration reported as HCO3- (g/litre). However the sit database do not contain HCO3 as the main master species. As not having a fresh water conditions the definition of carbon in system as "alkalinity" seems to me not reasonable vs. definition of somewhat increased "C" giving the subsequent HCO3- concentration in solution equal to measured one.

I would be very grateful for any comment on this issue.

[dlparkhurst]

When you define Alkalinity, PHREEQC adjusts the carbon (C(4)) concentration to generate a sum of alkalinity species equal to the specified alkalinity value. Note that borate, silica, OH-, and other species can contribute to the measured alkalinity.

I think that using Alkalinity in the input for SOLUTION does what you describe.

[ANar]

Thank you David, for clarification.
I started printing out total alkalinity calculated by PHREEQC and I see that PHREEQC does as you said - it adjust C concentration taking into consideration the input to alkalinity from other species (defined in the solution block).
The issue remains on what is actually measured and reported (hiding behind reported HCO3- value).

Thanks for quick response!