Vrije Universiteit Brussel
1050 Brussels | Belgium
Study of biogeochemical processes in sediment microniches using novel in situ techniques
Most organic matter (OM) input to aquatic sediments is in the form of marine snow particles which settle down through the water column. In addition, there is direct input at the sediment/water interface of OM that results from degradation of dead benthic fauna. Because the OM input is aggregated, this engenders that the sedimentation of labile organic material is highly spatially heterogeneous at the sediment water interface (SWI). After microbial colonization, rapid rates of organic carbon mineralization have been observed within microniches ranging from 1 to 10 mm in diameter. Classic squeezing or centrifugation of pore water from sediment cores provides a spatially averaged picture of the pore water geochemistry (horizontal averaging ~10 cm, vertical averaging ~ 1 cm), which is far larger than the size of the microniches. Accordingly, the intrinsic spatial heterogeneity is averaged within the volume of each sediment slice, and hence, any steep concentration gradients within the sediment will be missed. The averaged sediment section often includes different redox regimes and mixing of the various pore water parcels can induce chemical reactions that alter the original, in situ concentrations of the redox reactive species. Up until present, there are only a few incubation studies that have focusing on the impact of microniches on the degradation of OM and the sedimentary oxygen consumption. Equally, there are also a few studies dealing with the simultaneous measurements of spatial distribution of sulphide and trace metals in microniches. This PhD project is to unravel and to better understand biogeochemical cycles of trace metals influenced by organic matter deposition and variations of pH and O2 concentrations in microniches in aquatic sediments.
Belgian Coastal Zone (North Sea, Belgium)
trace metals, laser ablation-ICP-MS, DGT, O2/pH optode, dissolved sulfide, microniches