The water quality fluxes currently modelled in Source are the exchanges of water quality constituents between river reaches (i.e. links) and groundwater. The modelling approach allows for exchanges from the river to groundwater or from groundwater to the river. Details of the approach is available via Flux - SRG
For modelling storages the water mass balance equation includes a term for loss (seepage) to, or gain from, groundwater (see Storage node - SRG). When modelling water quality constituents, the constituent mass balance equation contains an equivalent term.