DETERMINATION OF ABSORPTION AND FLUORESCENCE
EXCITATION SPECTRA FOR PHYTOPLANKTON
B.G.MITCHELL and D.A. KIEFER
Department of Biological Sciences, University of Southern
California, Los Angeles, California 90089, USA.
I.
INTRODUCTION
Investigations of photosynthetic processes in both aquatic ecosystems and in the laboratory have sought to couple measurements of the
rates of production with quantitative assessment of the ambient light
field and the absorption capacity of the cells. Kiefer etal. (1979) and
Bricaud etal. (1983) have described techniques for determination of absorption coefficients for cultures. For field studies, however, where
the cell concentration is very dilute, direct measurement of absorption
is not possible. Most field studies have assumed a constant absorption
per chlorophyll, and have estimated the amount of absorbed light from
measurements of the chlorophyll concentration and the available light for
photosynthesis (Rhode,1965; Tyler,1975; Dubinsky and Berman,1976; Morel,
1978). We present here a technique for measuring the absorption coefficient (a ) for cultures or field samples. Yentsch (1957) first applied
p
the technique of direct measurement of absorption on filters for algal
cultures, and for qualitative analysis of suspended marine particulates
(1962). Faust and Norris (1982) have used derivative absorption spectroscopy of cultured phytoplankton on glass fiber filters in order to assess
pigment concentration. The problem with measurement on filters is that
the optical environment has been modified and corrections for the effects
this has on the measurement must be made if quantitative applications are
desired. Kiefer and SooHOo (1982) have described a correction which estimates the amplification effect due to scattering by glass fiber filters.
A more accurate technique for correcting this effect is described here.
In addition to making routine measurements of a in the field and
p
lab, we have also developed an inexpensive and simple spectrofluorometer
capable of rapidly measuring fluorescence excitation spectra of chlorophyll ~ contained in particles retained on filters.
Yentsch and Yentsch
(1979) used spectra which were uncorrected for the system response to
EXCITATION SPECTRA FOR PHYTOPLANKTON
B.G.MITCHELL and D.A. KIEFER
Department of Biological Sciences, University of Southern
California, Los Angeles, California 90089, USA.
I.
INTRODUCTION
Investigations of photosynthetic processes in both aquatic ecosystems and in the laboratory have sought to couple measurements of the
rates of production with quantitative assessment of the ambient light
field and the absorption capacity of the cells. Kiefer etal. (1979) and
Bricaud etal. (1983) have described techniques for determination of absorption coefficients for cultures. For field studies, however, where
the cell concentration is very dilute, direct measurement of absorption
is not possible. Most field studies have assumed a constant absorption
per chlorophyll, and have estimated the amount of absorbed light from
measurements of the chlorophyll concentration and the available light for
photosynthesis (Rhode,1965; Tyler,1975; Dubinsky and Berman,1976; Morel,
1978). We present here a technique for measuring the absorption coefficient (a ) for cultures or field samples. Yentsch (1957) first applied
p
the technique of direct measurement of absorption on filters for algal
cultures, and for qualitative analysis of suspended marine particulates
(1962). Faust and Norris (1982) have used derivative absorption spectroscopy of cultured phytoplankton on glass fiber filters in order to assess
pigment concentration. The problem with measurement on filters is that
the optical environment has been modified and corrections for the effects
this has on the measurement must be made if quantitative applications are
desired. Kiefer and SooHOo (1982) have described a correction which estimates the amplification effect due to scattering by glass fiber filters.
A more accurate technique for correcting this effect is described here.
In addition to making routine measurements of a in the field and
p
lab, we have also developed an inexpensive and simple spectrofluorometer
capable of rapidly measuring fluorescence excitation spectra of chlorophyll ~ contained in particles retained on filters.
Yentsch and Yentsch
(1979) used spectra which were uncorrected for the system response to