  The paper is concerned with guaranteed a posteriori error estimates for a
class of evolutionary problems related to poroelastic media governed by the
quasi-static linear Biot equations. The system is decoupled employing the
fixed-stress split scheme, which leads to a semi-discrete system solved
iteratively. The error bounds are derived by combining a posteriori estimates
for contractive mappings with those of the functional type for elliptic partial
differential equations. The estimates are applicable for any approximation in
the admissible functional space and are independent of the discretization
method. They are fully computable, do not contain mesh dependent constants, and
provide reliable global estimates of the error measured in the energy norm.
Moreover, they suggest efficient error indicators for the distribution of local
errors, which can be used in adaptive procedures.
