RESUMEN
Water flow through model porous media was studied in the presence of surface relaxation, internal magnetic field inhomogeneities and exchange with stagnant water pools with different relaxation behavior, demonstrating how the apparent flow parameters average velocity, volume flow and flow conducting area in these situations depend on the observation time. To investigate the water exchange process a two component biological model system consisting of water flowing through a biofilm reactor (column packed with methanogenic granular sludge beads) was used, before and after a heat treatment to introduce exchange. We show that correction of the stagnant fluid signal amplitude for relaxation at increasing observation time using the observed relaxation times reveals exchange between the two fractions in the system. Further it is demonstrated how this exchange can be quantified.