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Fluorescence of DOM nanoparticles in natural water

Non-living dissolved organic matter (DOM) is the largest organic carbon pool in natural waters and plays a central role in the biogeochemistry of a variety of elements. Colloidal matter makes up a significant portion of the bulk DOM in aquatic environments, but is still poorly characterized. Fluorescence emission spectra excited at 270, 310 and 355 nm and absorbance values were measured for the colloidal fraction CF with particles size ranging between 5 and 200 nm, for the fraction F5 with molecules smaller 5 nm, and for DOM filtered with the 0.2 μm pore size filter. For all DOM fractions the "blue shift" of fluorescence maximum position was observed with excitation at 310 nm compared to excitation at 270 or 355 nm. With river water samples it was found that DOM contains about 40% of organic matter in colloidal fraction; that emission maximum wavelength is 5...10 nm longer for CF than for F5; that fluorescence quantum yield is decreasing in 12% for CF and increasing in 30% for F5 compared to the original DOM samples. We confirmed that bigger DOM nanoparticles have red-shifted fluorescence emission and lower fluorescence quantum yield compared to DOM nanoparticles smaller 5 nm.