Abstract
Field measurements of chlorophyll-a (Chl), phycoerythrin (PE), chromophoric dissolved organic matter (CDOM), and variable fluorescence (F(v)/F(m)) in diverse waters of the California Current, Mediterranean Sea and Gulf of Mexico using 375, 405, 510 and 532 nm laser excitation wavelengths (EW) are analyzed. EW = 375 and 405 nm were found more suitable for Chl assessment in high-Chl (> 10 μg/l) waters. Both EW = 532 and 510 nm can be used to efficiently stimulate PE fluorescence for structural characterization of phytoplankton communities. EW = 375 nm and 405 nm can provide best results for CDOM assessments in offshore oceanic waters; the green EWs can be also used for CDOM measurements in fresh and estuarine water types in conjunction with spectral discrimination between CDOM and PE fluorescence. Both EW = 405 and 510 are suitable for photo-physiological F(v)/F(m) assessments, though using EW = 405 nm may result in underestimation of PE-containing phytoplankton groups present in mixed phytoplankton assemblages.
Highlights
Actively-stimulated fluorescence of natural waters can provide rich information about aquatic fluorescence constituents, including phytoplankton, chromophoric dissolved organic matter (CDOM; see a table of abbreviations in the Appendix), oil and poly-aromatic hydrocarbons (PAHs)
Our analysis of chlorophyll a (Chl) fluorescence measurements with EW = 375, 405, 510, and 532 nm shows that each of these excitation wavelengths can be used for accurate assessment of Chl biomass in coastal and offshore oceanic waters
Our field measurements of Chl, phycoerythrin, CDOM, and variable fluorescence in diverse waters of the California Current, Mediterranean Sea and Gulf of Mexico using 375, 405, 510 and 532 nm laser excitation have shown that each of these excitation wavelengths can be used for accurate assessment of Chl concentration in coastal and offshore oceanic waters
Summary
Actively-stimulated fluorescence of natural waters can provide rich information about aquatic fluorescence constituents, including phytoplankton, chromophoric dissolved organic matter (CDOM; see a table of abbreviations in the Appendix), oil and poly-aromatic hydrocarbons (PAHs). The 510 nm excitation allows assessment of the key aquatic fluorescence characteristics, such as Chl and PBP pigments, as well as variable fluorescence [45] (the latter was not possible with 532 nm laser due to technological limitations [5]) The use of both 510 nm and 405 lasers in the ALF-T instrument provided new analytical capabilities, such as Fv/Fm measurements with alternate blue/green excitation for more representative photophysiological assessments of various phytoplankton groups. While both 375 and 510 nm lasers were successfully tested in the laboratory [45,46], it was important to evaluate the new excitation sources in the field conditions. Some results can be used for optimizing the design and measurement protocols of LED- and lamp-based fluorometers
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