BioGeoChemistry of Tidal Flats


K. W. Wirtz, J. Holstein, J. Staneva

Model hindcasts for an aquifer release of anaerobic chemical and microbial species into tidal waters

It is commonly believed that biogeochemical processes in deeper sediment layers evolve independently from the pelagic system, and vice versa. This view is here questioned using a two-stage approach where data are combined with a set of models. In the first stage, the Integrated Sediment Model (ISM) which resolves microbial, geochemical and physical benthic processes is employed and several hypothesis are tested insofar they can explain deep maxima in sulfate and ammonium concentrations observed in the Spiekeroog backbarrier reef. We show that the data can be best explained supposing a subterranean aquifer flow that imports sulfate and exports diagenesis products such as methane. With the ISM an outflux range for chemical and microbial species can be estimated. In the second stage of the analysis, the outflow is linked to a time series of methane taken at a distant pile station (Grunwald et al, submitted to SS48). A tracer model for hydrodynamical transport in tidal flats yields constraints for the outflow location, the aerobic methane oxidation rates, the temporal nature of the aquifer release and for the occurrence of anaerobic microbes.