DOC, absorption and fluorescence properties of estuarine and coastal waters of the Northern Tyrrhenian Sea

Estuarine and coastal waters of a selected area of the Tyrrhenian Sea were analysed for dissolved organic carbon (DOC), absorption and fluorescence properties. Coastal DOC values ranged from 0.88 to 1.37 mg L−1 with an average of 1.1 mg L−1. Absorption coefficients measured at 280 nm (a280) and 355 nm (a355) were in the range 0.95–2.3 m−1 (average 1.52 m−1) and 0.14-0.57 m−1 (average 0.27 m−1), respectively. The slope of the log-linearized absorption spectra, S, ranged from 0.012 to 0.029 nm−1 with a mean value of 0.019 nm−1. Normalized fluorescence, excited at the same wavelengths of the absorption measurements, Fn(280) and Fn(355), exhibited mean values of 0.07 and 0.77 N.Fl.U., and the quantum yields, Ф280 and Ф355, had mean values of 0.0014 and 0.0065, respectively. The chromatographic behavior of a riverine and a coastal sample, compared with that of a solution of commercial humic acid, used as standard, shows a variation in the chromatographic signature to which corresponds a decrease in the apparent molecular weight (Mr). Also taking into account the solar radiation regime of the sample collection period, these data show the occurrence of a CDOM (chromophoric dissolved organic matter) fluorescence photobleaching just in the first few miles off the coast.