A method for the experimental determination of light absorption by aquatic heterotrophic bacteria

A method has been set up for the experimental determination of the volume coefficient for light absorption in vivo by aquatic heterotrophic bacteria. The application described here is the absorption measurement of the bacterial fraction that passes through the commonly used GF/F filter and remains unaccounted for. The experimental samples were prepared by successive water nitra- tions through GF/F and 0.22 urn Millipore membranes. Light-transmission and light-reflection measurements of the filter-retained samples were performed using a dual-beam spectrophotometer equipped with an integrating sphere attachment. Sample absorption was derived from the data by a procedure that corrects for the contamination of the results due to the high degree of light scattering by the bacteria. The bacterial absorption was discriminated from fine detritus absorption by bleaching the bacterial respiratory pigments using a K^Og solution. The absorption amplification caused by multiple scattering in the filter was corrected for by an expression that was obtained experimentally. A test of the method, including error analysis, was performed on samples collected in both marine and inland waters. The relative contributions to light absorption by heterotrophic bacteria and various types of paniculate matter were also measured for a typical situation. Combining the measured volume absorption coefficients with backscattering coefficients computed by Mie theory yields a set of input data to multicomponen t optical models that is needed to assess the contribution of these heterotrophic bacteria to the radiative transfer process.

[1]  A. Bricaud,et al.  Spectral absorption coefficients of living phytoplankton and nonalgal biogenous matter: A comparison between the Peru upwelling areaand the Sargasso Sea , 1990 .

[2]  R. Poole,et al.  10 The Analysis of Cytochromes , 1985 .

[3]  L. Prieur,et al.  An optical classification of coastal and oceanic waters based on the specific spectral absorption curves of phytoplankton pigments, dissolved organic matter, and other particulate materials1 , 1981 .

[4]  Stelvio Tassan,et al.  An alternative approach to absorption measurements of aquatic particles retained on filters , 1995 .

[5]  H. Claustre,et al.  Prochlorococcus and Synechococcus: A comparative study of their optical properties in relation to their size and pigmentation , 1993 .

[6]  A. Weidemann,et al.  Quantifying absorption by aquatic particles: A multiple scattering correction for glass-fiber filters , 1993 .

[7]  Motoaki Kishino,et al.  Estimation of the spectral absorption coefficients of phytoplankton in the sea , 1985 .

[8]  F. Azam,et al.  Biogeochemical significance of bacterial biomass in the ocean's euphotic zone , 1990 .

[9]  T. Platt,et al.  Light scattering by marine heterotrophic bacteria , 1992 .

[10]  Y. Ahn,et al.  Optical efficiency factors of free-living marine bacteria: Influence of bacterioplankton upon the optical properties and particulate organic carbon in oceanic waters , 1990 .

[11]  Dale A. Kiefer,et al.  Optical properties of marine bacteria , 1990, Defense, Security, and Sensing.

[12]  H. Gordon,et al.  Remote Assessment of Ocean Color for Interpretation of Satellite Visible Imagery: A Review , 1983 .

[13]  Dale A. Kiefer,et al.  Chlorophyll α specific absorption and fluorescence excitation spectra for light-limited phytoplankton , 1988 .

[14]  Dale A. Kiefer,et al.  Light scattering by microorganisms in the open ocean , 1991 .

[15]  S. Tassan,et al.  Use of the 0.22 μm Millipore membrane for light-transmission measurements of aquatic particles , 1996 .

[16]  M. Doudoroff,et al.  The Microbial World , 1977 .

[17]  L. Prieur,et al.  A three-component model of ocean colour and its application to remote sensing of phytoplankton pigments in coastal waters , 1989 .