How to increase surface pH with algal growth in AEM3D Water Quality Module

Question

The simulation of pH in CAEDYM was pretty easy and straight-forward.  The trend of surface pH simply follows algal growth.  During the algal growth season, surface pH goes up. After the algal growth season, surface pH goes down.  Bottom pH mostly stays relatively constant.  As I remember, we usually didn't need to do much about pH, at most adjusting intial conditions.  However, in the new water quality module of AEM3D, the simulation of DIC and pH seems more complicated.  I tried quite a few things in the model, but couldn't change pH results, which basically stayed constant on both surface and bottom even though there was algal growth at surface (up to 10 ug/L each year). Can someone please point out what settings that I need to change for pH to increase with algal growth?  Thanks!

Answer 1

HI,

I've recently added some functionality to the pH/DIC routines.  I've added the ability to use an iterative solution similar to the CQUAL model.  This treats TOTAL_ALKALINITY as a conservative state variable that needs to be initialised and have BC values.  It seams to be working better for the cases we've tried.

To use this version add

CQUAL_BRENT ph_iteration_method

 to your carbon file.