| Summary: | Continental shelves are characterised by an active benthic system which is closely coupled to the pelagic: hence, the distinction between new and recycled production is not clear since the short and long-term processes are effectively coincident in space. In shelf ecosystems up to 40% of phytoplankton production can settle to the seabed and a large proportion of organic matter remineralisation occurs in the benthic compartment. However the benthic response of phytoplankton sedimentation is not unique and the receiving sediment type is a key factor determining the organic matter remineralisation rates. The aim of this project was to determine the relative importance of benthic regeneration processes at the Stonehaven monitoring site, Scotland, UK. Single and multi-beam acoustic and ground truthing surveys were carried out in the study area and the seabed landscape was described by sediment classes ranging from muddy sand to boulders and rock. General additive models were developed to link full coverage acoustic properties with sediment chemical concentrations developing full coverage maps of organic matter sources identifying the factors that can influence them. Direct measurements of sediment-water fluxes were carried out at monthly intervals throughout the year at a selected number of sampling stations identified by the acoustic analysis. The results revealed that water temperature, turbidity, sediment chlorophyll-a content and permeability were the main drivers of sediment biogeochemistry. Sediment nutrient regeneration rates contributed to the water annual budget of 25% and 89% for nitrogen and silicate respectively. Contrarily the sediment was a net sink for phosphate suggesting the importance of external supplying sources for this element. Finally, using a combined statistical modelling, we up-scaled results from a limited number of stations developing full coverage biogeochemical maps in the study area identifying 'hot spot' of sediment activity in a depositional area characterised by fine-grained sediment.
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