Controlled artificial upwelling in a fjord to stimulate non-toxic algae

摘要: Abstract During the summer, primary production in surface layers of some fjords depletes nutrients to degree that species toxic algae can dominate. We describe field experiments employing a bubble curtain and submerged freshwater outlet lift significant amounts nutrient-rich seawater light zone provide an environment which non-toxic bloom. The motivation for experiment is local region with stimulated growth phytoplankton thereby creating possibility mussels be cleansed from effects algae. In first experiment, 100-m long curtain, using three perforated pipes 40 m depth, was operated Arnafjord, side arm Sognefjorden western Norway. An air supply 44 Nm 3 each minute lifted 65 m /s deeper upper layer intense mixing during period weeks. mixed water flowed at depths 5 15 m. Within few days, mixture covered most inner portion Arnafjord. second deep, 26 m discharge Jostedal hydropower plant Gaupnefjord, another Sognefjorden, manipulated enhance upwelling by diffuser plate. increased entrainment buoyant plume led intrusion into compensation current 5–10 m depth longer residence time fjord arm. showed 117 m rising compared 140 m obtained small-scale laboratory simulation, implying sub-optimal placement plate over plume. This, however, still more energy-efficient than curtain. both (bubbles discharge) nutrient inputs resulted relative reduction