Reactions occur during drainage stage only (gas phase)

The HP1 code incorporates modules simulating
(1) transient water flow in variably-saturated media,
(2) transport of multiple components, and
(3) mixed equilibrium/kinetic geochemical reactions.
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tuviat
Posts: 3
Joined: Tue Jan 19, 2021 6:59 am
Location: Israel

Reactions occur during drainage stage only (gas phase)

Post by tuviat » Sun Feb 26, 2023 3:54 pm

Dear All,
I run water, heat, solute and gaseous oxygen transport models using HP1 for MAR conditions.
After I finished to calibrate the physical properties of my site, I started to run nitrification reactions as well. However, the nitrification processes occur only when no water are ponding on top of the soil surface (the drainage stage).
I'm not sure if there is a definition in phreeqc where the liquid and the gas phases should be pre-defined (I didn't find something specific).
I will be happy to hear your suggestions.
Cheers,
Tuvia

diederik
Posts: 71
Joined: Fri Mar 10, 2006 7:57 am
Location: Belgium

Re: Reactions occur during drainage stage only (gas phase)

Post by diederik » Mon Feb 27, 2023 7:51 am

what do you exactly mean with predefnied?

tuviat
Posts: 3
Joined: Tue Jan 19, 2021 6:59 am
Location: Israel

Re: Reactions occur during drainage stage only (gas phase)

Post by tuviat » Mon Feb 27, 2023 8:59 am

Hi
I think that there is a problem of how I define dissolved oxygen and the gaseous oxygen. However, I'm not sure where to correct this issue.
Under flooding conditions, there is zero gaseous oxygen in the soil, and the dissolved oxygen in the flowing solution would be the only source. Following the drainage (the drying stage), the gaseous oxygen is intrude to the soil and the dissolved oxygen is a function of Henry's law.
I find it difficult to define these to processes in one run, that includes flooding and drainage.
Do you have a suggestion?
Cheers,
Tuvia

diederik
Posts: 71
Joined: Fri Mar 10, 2006 7:57 am
Location: Belgium

Re: Reactions occur during drainage stage only (gas phase)

Post by diederik » Mon Feb 27, 2023 1:23 pm

Hi,

In the geochemical model for the soil, you need to define both a solution and a gas phase (if there is no gas phase, you will have only O2 diffusion in solution phase).
In the upper boundary condition, you will have to define also a gas phase (with a boundary_layer) (and if you have an incoming solution, the concentration there should be defined via Henry's law).

In the HP1 / HPx help file you find how to simulate diffusion in the gas phase (How To ..., Gas diffusion)

diederik

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