Effects of progressive oxygen depletion on sediment diagenesis and fluxes: A model for the lower St. Lawrence River Estuary

where Eq. A1.1a is for dissolved species, and Eq. A1.1b is for solid species. Here, t is time, and x is the depth coordinate below the sediment–water interface. U is the advection (burial) velocity. Rj values are the rates of chemical and biochemical reactions, and nij is the stoichiometric coefficient of species i in reaction j. Q is the sediment porosity. The factor j is equal to (1 2 Q)r, where r is the density of dry sediment in g cm23. The effective diffusion coefficients Di for solutes were calculated as sums of the bioturbation coefficient Db and the appropriate molecular diffusion coefficients, which were corrected for sediment porosity using an Archie’s law factor of Q1.14 (Boudreau 1997), for salinity as described in Burdige (2006), and for temperature of T 5 5uC using expressions in Boudreau (1997). The rate constants for the rates Rj of chemical and biochemical reactions (Tables A1.1–A1.3) were taken from dSED, a database for modeling sediment diagenesis (Katsev et al. 2004). The coefficient airr(x) describes bioirrigation, Ci is the dissolved substance concentration at the sediment–water interface, and Ci is the concentration of that substance in a bioirrigated burrow (see following). The boundary conditions at the sediment–water interface are imposed concentration (Dirichlet) for the dissolved species: