Interpretation of the fluorescence signature of marine, coastal and estuarine waters

    Parlanti E. (1), C. Belin (1), S. Patsayeva (3), M. Ewald (1) and M. Lamotte (1)

    (1) : Universite de Bordeaux I, LPPM, URA CNRS 348, F-33405 TALENCE, France
    (2) : Universite de Caen, Department de Geologie, F-14032 CAEN, France
    (3) : Moscow State University, Physics Department, MOSCOW 119899, Russia.

    Although humic substances in freshwater and sea water have dissimilar sources and differ chemically, reports of differences in their spectral properties in relation with their origins are still subject to controversy and have not yet lead to current application for distinguishing between continental and marine DOMS.

    In this paper we report on the investigation of the fluorescence spectra and intensity of water samples collected in the Seine, its estuary and in several stations in the bay of Seine and coastal vicinity. Comparison of water mass fluorometric properties was made on the basis of spectra and fluorescence intensities obtained with excitation at 270, 313 and 370 nm. The results are discussed in conjunction with data obtained on the same samples for chlorophyll and dissolved organic carbon (DOC) concentrations.

    The results show evidence for a continuous change of the water fluorescence properties in going from continental to marine waters. A linear variation of the fluorescence intensity versus salinity has been observed for excitation at 370 nm, a result which is in agreement with what is currently observed in estuaries and which is indicative of a conservative behaviour of continental DOM during mixing with marine waters.

    Excitation at 313 nm has revealed the presence in the DOM fluorescence spectra of two classes of characteristic fluorescent organic matter. The first one is responsible for the long wavelength part of the fluorescence emission has been assigned to humic substances (A component, lmax @ 380-440-450 nm) and is predominant in continental waters. The second one contributes to broaden the emission spectra in the short wavelength side (B component, lmax @ 380-400 nm) and is mainly observed in the marine samples. Comparison with the fluorescence of marine algae exsudats separated by HPLC lead to propose that the B component could be assigned to recently degraded marine algae exsudats.