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Microalgal photosynthesis and spectral scalar irradiance in coastal marine sediments of Limfjorden, Denmark
Author(s) -
Lassen Carsten,
Ploug Helle,
Jorgensen Bo Barker
Publication year - 1992
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1992.37.4.0760
Subject(s) - irradiance , photic zone , photosynthesis , cyanobacteria , phycocyanin , bacteriochlorophyll , chlorophyll a , light intensity , oceanography , biology , geology , botany , phytoplankton , physics , ecology , optics , paleontology , nutrient , bacteria
Scalar irradiance and oxygenic photosynthesis were measured simultaneously at 100‐µm spatial resolution by a fiber‐optic scalar irradiance microsensor and an oxygen microelectrode spaced 120 µm apart. Marine microbial mats on sandy sediments along the coast of Limfjorden, Denmark, were dominated by cyanobacteria with a surface layer populated by pennate diatoms. In dim light Oscillatoria sp. migrated upward and a dense surface film of cyanobacteria developed. The spectral distribution of scalar irradiance showed absorption peaks at 430 and 675 nm (Chl a ), 630 (phycocyanin), and 800 and 860 nm (bacteriochlorophyll a ). Infrared scalar irradiance reached 200% of incident light intensity at 0.0–0.3‐mm depth and IR penetration was independent of the development of a cyanobacterial surface film. At high incident light intensity, 740 µ Einst m −2 s −1 , the photosynthetic efficiency at 1.0‐mm depth was 10‐fold higher than in the uppermost 0.0–0.6 mm of the sediment. The lower boundary of the euphotic zone (detectable gross photosynthesis) was at a mean light level of ≥7.5 µ Einst m −2 s −1 .