* The source an sink terms link the mass balances of the n-transported component to the
* solid phases. The porosity \f$\phi\f$ is updated according to the reduction of the initial * (or solid-phase-free porous medium) porosity \f$\phi_0\f$ by the accumulated volume
* fractions of the solid phases:
* \f$ \phi = \phi_0 - \sum (\phi_\lambda)\f$
* Additionally, the permeability is updated depending on the current porosity.