Sediment-Water Column Coupling and the Fate of the Spring Phytoplankton Bloom in Loch Linnhe, a Scottish Fjordic Sea-loch. Sediment Processes and Sediment-Water Fluxes

Sediment-water fluxes of oxygen and nutrients before and after the impact of the spring phytoplankton bloom were measured by core incubation experiments. Less than 10 days after the bloom had settled, chlorophyll was found down to a depth of 2 cm in the sediment. This rapid burial was probably due to mixing during resuspension events. There was some increase in oxygen uptake by the sediment after settlement of the bloom and a concomitant increase in the apparent oxygen diffusion coefficient; this latter increase may indicate a stimulation of bio-irrigation. There was a nitrate influx after settlement of the bloom, but no measurable efflux of ammonium or phosphate from the sediment. There was no increase of sulphate reduction activity after the impact of the bloom nor was solid-phase extractable manganese used as an alternative terminal electron acceptor for oxidation of carbon. We conclude that much of the readily biodegradable organic components of the bloom was mineralized in the water column during sediment resuspension events.