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

David McKee, Alex Cunningham, Ken Jones

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Abstract

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
JournalJ PLANKTON RES
Issue number4
DOIs
Publication statusPublished - 2002

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Keywords

  • DYNAMICS
  • ECOSYSTEM
  • WATER
  • BLOOMS
  • DEPTH
  • Marine & Freshwater Biology
  • STRIVEN
  • Oceanography
  • LOCHS
  • CLYDE SEA

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