Optical and hydrographic consequences of freshwater run-off during spring phytoplankton growth in a Scottish fjord

David Mckee, Alex Cunningham, Ken J. Jones

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A combination of in situ measurements and radiative transfer modelling were used to study optical conditions in the inner basin of Loch Etive, a Scottish fjord, in March and April 2000. The basin was strongly stratified with three layers separated by marked pycnoclines. The surface layer averaged 5 m in depth and was heavily stained with coloured dissolved organic matter (CDOM) which reduced the euphotic depth to between 7 and 10 m. Approximately 20% of the photosynthetically available radiation (PAR) in the water column was absorbed by phytoplankton, 44% by CDOM and 36% by sea water. Detectable concentrations of the major inorganic nutrients (nitrate, phosphate and silicate) occurred at all depths, but significant phytoplankton populations (averaging 6 mg chlorophyll a m-3) were found only in the reduced-salinity surface layer. The freshwater input therefore acted both as a source of buoyancy which promoted phytoplankton growth near the surface and as an attenuator of visible light which inhibited growth deeper in the water column.

Original languageEnglish
Pages (from-to)1163-1171
Number of pages9
JournalJournal of Plankton Research
Issue number11
Publication statusPublished - 1 Nov 2002


  • Loch Etive
  • Scottish fjord
  • pycnoclines
  • phytoplankton population-dynamics

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