Article (Scientific journals)
Mathematics of the total alkalinity–pH equation – pathway to robust and universal solution algorithms: the SolveSAPHE package v1.0.1
Munhoven, Guy
2013In Geoscientific Model Development, 6, p. 1367-1388
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Keywords :
pH; Alkalinity; equation solving
Abstract :
[en] The total alkalinity–pH equation, which relates total alkalinity and pH for a given set of total concentrations of the acid–base systems that contribute to total alkalinity in a given water sample, is reviewed and its mathematical properties established. We prove that the equation function is strictly monotone and always has exactly one positive root. Different commonly used approximations are discussed and compared. An original method to derive appropriate initial values for the iterative solution of the cubic polynomial equation based upon carbonate-borate-alkalinity is presented. We then review different methods that have been used to solve the total alkalinity–pH equation, with a main focus on biogeochemical models. The shortcomings and limitations of these methods are made out and discussed. We then present two variants of a new, robust and universally convergent algorithm to solve the total alkalinity–pH equation. This algorithm does not require any a priori knowledge of the solution. SolveSAPHE (Solver Suite for Alkalinity-PH Equations) provides reference implementations of several variants of the new algorithm in Fortran 90, together with new implementations of other, previously published solvers. The new iterative procedure is shown to converge from any starting value to the physical solution. The extra computational cost for the convergence security is only 10–15% compared to the fastest algorithm in our test series.
Research center :
Laboratiore de Physique Atmosphérique et Planétaire
Disciplines :
Earth sciences & physical geography
Physical, chemical, mathematical & earth Sciences: Multidisciplinary, general & others
Author, co-author :
Munhoven, Guy ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP)
Language :
English
Title :
Mathematics of the total alkalinity–pH equation – pathway to robust and universal solution algorithms: the SolveSAPHE package v1.0.1
Publication date :
2013
Journal title :
Geoscientific Model Development
ISSN :
1991-959X
eISSN :
1991-9603
Publisher :
Copernicus GmbH
Volume :
6
Pages :
1367-1388
Peer reviewed :
Peer Reviewed verified by ORBi
Funders :
F.R.S.-FNRS - Fonds de la Recherche Scientifique [BE]
Commentary :
Revised versions of the SolveSAPHE Fortran library with bug fixes are available on Zenodo under https://www.zenodo.org/record/3752250 (DOI: 10.5281/zenodo.3752250).
Available on ORBi :
since 11 September 2013

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