Advanced laser fluorometry of natural aquatic environments

Alexander Chekalyuk, Mark Hafez

Limnol. Oceanogr. Methods 6:591-609 (2008) | DOI: 10.4319/lom.2008.6.591

ABSTRACT: The Advanced Laser Fluorometer (ALF) provides spectral deconvolution (SDC) analysis of the laser-stimulated emission (LSE) excited at 405 or 532 nm for assessment of chlorophyll a, phycoerythrin, and chromophoric dissolved organic matter. Three spectral types of phycoerythrin are discriminated for characterization of cyanobacteria and cryptophytes in mixed phototrophic populations. The SDC analysis is integrated with measurements of variable fluorescence, Fv/Fm, corrected for the SDC-retrieved background fluorescence, BNC, for improved photophysiological assessments of phytoplankton. The ALF deployments in the Atlantic and Pacific Oceans, and Chesapeake, Delaware, and Monterey Bays revealed significant spectral complexity of LSE. Considerable variability in chlorophyll a fluorescence peak, 673-685 nm, was detected. High correlation (R2 = 0.93) was observed in diverse water types between chlorophyll a concentration and fluorescence normalized to water Raman scattering. Three unidentified red bands, peaking at 625, 644, and 662 nm, were detected in the LSE excited at 405 nm. Significant variability in the BNC/chlorophyll a ratio was observed in diverse waters. Examples of the ALF spectral correction of Fv/Fm, underway shipboard measurements of horizontal variability, and vertical distributions compiled from the discrete samples analyses are presented. The field deployments have demonstrated the utility of the ALF technique as an integrated tool for research and observations.