When using the new water quality module on initialisations must be done in using the standard methods (ie, the same way you would initialise a hydrodynamic scalar such as temperature).
These can be dune using the DEFAULT values in run_aem3d.dat or using any of the initialisation file types.
In the Round Lake example this variable is initialised in the run_aem3d.dat file in the line
0.04 DEFAULT_POCL_SED