When using Transport of Diluted Species in Porous Media (tds), the general equation can be:
where 
is diffusion and 
is convection or advection.
Now I want a solid species that works in the sediment itself 
:
where 
is biodiffusion/ bioturbation and 
is sedimentation or burial.
Is it simply making another tds physics where the porosity there is ?
Any other suggestions?
Many thanks,
Yaniv