Exchange of Nutrients and Oxygen between Sediments and Water Column: the Role of the Benthic Boundary Layer

The thesis focuses on the transport and transformation of nutrients and oxygen across the benthic boundary layer (BBL). The BBL denotes the water layer that is directly influenced by the interface between the sediment and the overlying water column and which is characterized by intense turbulent mixing, gradients in solutes and increased concentrations of suspended particulate matter. So far, the rates and regulation of nutrient exchange across and microbial activity within the BBL are poorly understood. The aim of this thesis is to characterize and quantify the vertical transport of nutrients and oxygen across the BBL as well as the microbial activity within the BBL. The vertical turbulent transport in the benthic boundary layer is subject of two Chapters of which one focuses on the measurement and interpretation of nutrient and oxygen concentration gradients in the BBL while the other focuses on the dynamics of turbulent flow in the BBL and its mixing efficiency. Microbial activity in the BBL is described for several different sites exhibiting oxic as well as suboxic bottom waters.