Ultraviolet-visible and fluorescence spectral evidence of natural organic matter (NOM) changes along an estuarine salinity gradient |
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| Authors: | Email author" target="_blank">James?J?AlbertsEmail author Monika?Takács John?Schalles |
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| Institution: | (1) Departamento de Ciências Exatas, Escola Superior de Agricultura  Luiz de Queiroz , University of São Paulo, ESALQ/USP, C.P. 09, 13418-900 Piracicaba (SP), Brazil;(2) Dipartimento di Biologia e Chimica Agroforestale ed Ambientale, University of Bari, Via G. Amendola, 165/A, 70126 Bari (BA), Italy; |
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| Abstract: | A transect of the St Marys River estuary from above the point of maximum salt wedge penetration to coastal salinities was
conducted in July 1999. None of the parameters examined—dissolved organic carbon (DOC) content, UV light absorbance at 254
nm, and Total Luminescence spectra—follow the rule of conservative mixing. The characteristics of the different molecular
size fractions of the St Marys River natural organic matter (NOM), as well as the results of a laboratory mixing experiment,
provided evidence that loss of larger molecular size compounds from riverine NOM may occur by coagulation at salinities up
to 10. An apparent gain of carbon in the lower estuary was attributed to exports from abundant coastal marshes in this area.
The Total Luminescence spectra of the riverine NOM can be described by two peaks, centered respectively around 340/445 nm,
and 230/430 nm Excitation/Emission Wavelength Pair (EEWP), which are characteristic of humic materials of aquatic origin.
The samples from the high salinity stations exhibit peaks at lower emission wavelength EEWP 320/424 nm, which can be considered
as marine humic-like material. The presence of amino acid-tryptophan like peaks were observed, with EEWP 300/350 nm in some
of the high salinity samples. This peak was of high relative fluorescence intensity. It is hypothesized that the intense biological
activity of the salt marsh and near coastal area is responsible for the carbon addition as well as the appearance of the highly
fluorescence amino acid-protein like material. |
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