Abstract
Detailed descriptions have been made of theunder-water light field based on continuousmeasurements of surface photon irradiance,calculations of losses by surface reflection andmeasurements of the vertical light attenuation. Thesemeasurements have been combined with measurements ofthe vertical distribution of phytoplankton chlorophylland the photosynthesis/irradiance curve to produce ameasurement of the daily integral of photosynthesis bynumerical integration using a PC spreadsheet; theaccuracy of the integrations is evaluated. The resultshave been compared with models that assume a uniformvertical distribution of phytoplankton. Suchassumptions produced underestimates of the dailyintegral of photosynthesis by 50–109% for apopulation of Aphanizomenon flos-aquae inthe Baltic Sea owing to the overestimate ofrespiratory losses. Buoyant cyanobacterial populationsfloat up during brief episodes of calm; this increasesthe insolation they receive and their resultantphotosynthetic activity may increase several times.These advantages of buoyancy, provided by gasvesicles, are a major factor in determining thesuccess of waterbloom-forming cyanobacteria. A modelis produced of the relationship between the mean depthof the Aphanizomenon phytoplankton populationand the daily integral of photosynthesis at differentinsolations; this may provide the basis forimprovement of models applicable to otherphytoplankton populations. The integration spreadsheetis available athttp://www.bio.bris.ac.uk/research/walsby/integral.htm.
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Walsby, A.E. Modelling the daily integral of photosynthesis by phytoplankton: its dependence on the mean depth of the population. Hydrobiologia 349, 65–74 (1997). https://doi.org/10.1023/A:1003045528581
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DOI: https://doi.org/10.1023/A:1003045528581