Influence of waves and current speed on resuspension of fish farm waste: Case study in Funningsfjørður, Faroe Islands

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The Faroe Islands is an archipelago situated in the Northeast Atlantic Ocean. One of the major industries is farming of salmonids. The farms are mostly located in bays and fjords that are sheltered from strong currents. The small distance between the fjords and the open ocean implies that many Faroese fjords are periodically exposed to ocean swells, especially during winter. Ocean swells are generally long period waves with motion reaching deep into the water column. When the swells are large enough they can add to the cleaning of fish farming sites by resuspension of the bottom sediments. In the present study the influence of swells on the bottom sediment in Funningsfjørður is investigated. By means of wave- and current measurements, combined with turbidity and sedimentation trap measurements, we found that wave action induced major resuspension events. Events with significant wave height above 2 m and peak periods of around 13 sec caused sediment at bottom depths of 54 m to be in suspension at < 14 m depth in the watercolum. However, current speeds of 15-20 cm s-1 near the seabed did not induce noteworthy resuspension of fish farm wastes. Sediment inventory combined with mineralization measurements of organic carbon indicated, that the influence of waves contributed to the removal of fish farm wastes from the seabed below the fish farm