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A THEORETICAL ANALYSIS OF THE CONTRIBUTION OF ALGAL CELLS TO THE ATTENUATION OF LIGHT WITHIN NATURAL WATERS
Author(s) -
KIRK J. T. O.
Publication year - 1976
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.1976.tb01524.x
Subject(s) - absorption (acoustics) , wavelength , spheroid , attenuation , prolate spheroid , particle (ecology) , volume (thermodynamics) , algae , oblate spheroid , physics , photosynthesis , phytoplankton , optics , chemistry , biology , botany , atomic physics , ecology , in vitro , biochemistry , classical mechanics , quantum mechanics , nutrient
SUMMARY A theoretical treatment of light attenuation within phytoplankton suspensions, developed in a previous paper, has now been extended to certain non‐spherical cells and colonies of diatoms, blue‐green and green algae. Procedures for calculating the mean absorption cross‐section for randomly oriented cells or colonies with the shape of cylinders, prolate spheroids or oblate spheroids, are described. The mean absorption cross‐sections at a series of wavelengths throughout the photosynthetic waveband are compared for model algae of various shapes, sizes and pigment compositions. The results clearly illustrate the principle that for a strongly absorbing algal cell/colony of a given volume, the more extended it is in space, the more effective it is as a light collector. The advantages of the more extended package are much less evident at wavelengths which are weakly absorbed. For algae of a compact, e.g. spherical, shape a large cell or colony captures much less light (of a wavelength which is strongly absorbed) than an equivalent volume of smaller cells. However, it is also true that a large particle of very extended shape, e.g. a long thin cylinder, can capture as much light as a greater number of smaller particles (of the same total volume) of more compact shape. This means that for purposes of light collection an alga is almost as well off when organized into long multicellular filaments as it would be if separated into a large number of single cells. Using the calculated values of mean absorption cross‐section the relationship between phytoplankton canopy structure and attenuation of photosynthetically active radiation (PAR) has been further investigated. Calculated values for the spectral distribution of light intensity, the total transmitted quantum flux, the vertical attenuation coefficients, and the increments in vertical attenuation coefficient per unit algal concentration, are presented for various model non‐scattering suspensions corresponding to common naturally‐occurring algae. The possible effects of turbidity on light attenuation in such systems are discussed.