Sediments are characterized by heterogeneous distributions of nutrients and microorganisms which emerge as a result of the interaction between chemical and biological processes with physical transport. We study in a simplified model the dynamics of one population of microorganisms and its nutrient, taking into account that the considered bacteria possess an active as well as an inactive state, where activation is processed by signal molecules. Furthermore the nutrients are transported actively by bioirrigation. It is shown that under certain conditions Turing patterns can occur which yield heterogeneous spatial patterns of species. Furthermore this model exhibits several stable coexisting spatial patterns. This phenomenon of multistability can still be observed when spatial patterns are externally imposed by considering a depth-dependent bioirrigation. The influence of bioirrigation on Turing patterns leads to the emergence of \'\'hot spots``, i.e. localized regions of enhanced bacterial activity.