The investigation of the transition zone between subsurface sediments and the water column, in addition to an enhanced understanding of the underlying processes, becomes more and more important when dealing with ecological questions not only in coastal areas. Therefore, DiaTrans (diagenetic transport), a one-phase/multi-component model to simulate multi-dimensional fully coupled density-driven flow, transport and biogeochemical reaction processes in the subsurface underlying a seawater column, including bioturbation and bioirrigation, is presented. The components include water and an arbitrary number of dissolved constituents such as chloride, methane, sulphate or oxygen. The governing equations are discretized using a Finite-Volume-Method (FVM) on two-dimensional rectangular structured grids in an object-oriented framework. A fully-upwinding technique is employed for the advective fluxes. The sparse and non-symmetric system of highly non-linear equations is solved, utilizing the Newton- Raphson method with an inner linear preconditioned BiCGSTAB solver. This implicit fully-coupled formulation of physical and biogeochemical processes, which has certain advantages, is a new approach not only in near-shore sediments, as generally decoupled methods are employed. The model accounts for different domain sizes and grid resolutions, unsteady conditions to simulate tidal cycles and variable physical parameters such as permeabilities and porosities which are important to cope with lateral heterogeneities.weiterlesen