Eight and seventeen bands were clearly fractionated with substantial different spectroscopic properties for fulvic acid and its methylene chloride extract by preparative thin layer chromatography. The fluorescence quantum yield of the bands ranged from 2% to 9.4%, almost 10 times that of natural humic substances. UV-vis, fluorescence spectra and fluorescence quantum yields revealed that each band was still a mixture.

Wavelength dependent "hole-burning" effect was observed for SRFA water and alcoholic solutions during exposure to laser of 457.9 nm and 488 nm. Absorptivity of the samples decreased but fluorescence intensity increased with time. New smaller chemicals with higher fluorescence quantum yield might be photoproduced. Both the degradation in absorbance and increase in fluorescence of SRFA alcoholic solution were higher than that of SRFA aqueous solution. The photochemical activity of SRFA was higher with 457.9 nm laser than with the 488 nm beam, and no photochemical activity with the 514.5 nm beam.

A direct solar irradiation was conducted for Lake Superior and Sturgeon River waters in Lake Superior. Water samples in quartz tubes were suspended in the lake at 0, 6.5 and 24 m for 5 or 15.5 h exposure to sunlight. DIC was produced while long wavelength absorbance decreased with irradiation time for lake water. For both river and lake samples, fluorescence decreased systematically. New chromophores with peaks at short wavelengths might be photoformed in lake samples. DOC concentrations in surface samples were lower than those at depth. Significant changes were observed even during a single day exposure to sunlight. Consecutive multi-step first-order photoreaction were found with different rate constant in each step. Fluorophores loss rate > chromophores loss rates > [DOC] loss rates.

Photochemical efficiency of UVB photons was separated from that of PAR photons for Lake Superior water through enhanced UVB and mimic solar irradiation and theoretical calculation. UV photons were much more efficient than visible photons on degrading DOC molecules. Fluorophores, chromophores and other parts of DOC in two water samples were all photodegradable through stepwise first-order reactions with decreasing rates. Fluorophores and chromophores were photodegraded faster than other DOC parts.