Modelling protocols for derivation of Fe(III) NICA constants and calculations of ambient Fe speciation and apparent Fe(III) solubility in seawater

Calculations of iron (Fe) speciation using the NICA-Donnan model can be useful for development of an understanding of the physico-chemical parameters (e.g. temperature, pH) that can influence Fe speciation in seawater (Hiemstra and van Riemsdjik. 2006; Gledhill et al. 2015; Avendano et al. 2016). Here we archive a protocol that can be used to calculate Fe speciation in seawater and derive new NICA constants for Fe binding to marine DOM, in combination with appropriately designed titration experiments. Importantly, for derivation of NICA constants, a pH dimension of sufficient resolution and breadth must be included in the experimental design. The protocol combines the chemical software ORCHESTRA with parameter estimation program PEST and was first described by (Janot et al. 2017) to successfully derive NICA constants for Cd and Zn binding to standard Laurentian Fulvic acid.

1. The Java program must be installed on your computer.

2. Calculations via chemical speciation software ORCHESTRA can be performed on Windows, Linux and Apple OSX, but the combination of PEST-ORCHESTRA can only be performed using Windows. We have only applied the software in Windows and the manual we have written is thus relevant to Windows and may not be applicable to use on Apple OSX or Linux.

PEST-ORCHESTRA.zip