Total luminescence spectra of IHSS standard and reference fulvic acids, humic acids and natural organic matter: comparison of aquatic and terrestrial source terms

Fulvic acids (6), humic acids (7) and natural organic matter (2) samples from the International Humic Substances Society Standards and Reference Collection were studied by total luminescence fluorescence spectroscopy (TLS). Two peaks generally characterize the spectra of all aquatic samples and the terrestrial fulvic acids, one with excitation wavelengths in the ultraviolet region of the spectrum (approx. 250 nm) and the other in the visible region of the spectrum with a broad range from 320 to 450 nm. However, terrestrial humic acid spectra contained one wavelength peak located at longer excitation-emission wavelength pairs (EEWP) relative to the aquatic samples and terrestrial fulvic acids, and other peaks that were not represented in the other samples. The relative fluorescence intensities (RFI) were significantly greater for fulvic acids than for humic acids. Relative fluorescence quantum efficiencies (RQE) were again significantly greater for the fulvic acids relative to humic acids, while the RQE of the natural organic matter (NOM) samples were intermediate between the fulvic and humic acids as was the case with the RFI data. Despite significant differences in climate and ecosystem types, no systematic differences were observed in the spectra of aquatic fulvic acids, aquatic humic acids or natural organic matter isolated from the southeastern US and Norway.