Comparison between humic-like peaks in excitation-emission matrix spectra and resin-fractionated humic substances in aquatic environments

The intensity of the 340/430-nm peak in the three-dimensional excitation-emission matrix spectra of water samples has been used as an index of the concentration of aquatic humic substance (AHS). However, whether this peak corresponds uniquely to AHS has not been definitively verified. Therefore, in this study, our objectives were: (1) to determine whether the 340/430-nm peak in the spectra of lake and river water samples does, in fact, correspond uniquely to AHS; (2) to determine what type of dissolved organic matter (DOM), in terms of hydrophobicity, accounts for the peak; and (3) to determine the advisability of using excitation-emission matrix spectroscopy to rapidly estimate AHS concentrations. We found that the 340/430-nm peak originates not only from the AHS fraction of DOM but also from a portion of the hydrophilic fraction. By analyzing the quantitative relationship between AHS concentration and 340/430-nm peak intensity for DOM samples, we found the intensity can be used to estimate AHS concentration in lake water when the concentration is strongly affected by influent river water or when the ratio of ultraviolet (UV) absorbance to dissolved organic carbon concentration is relatively high.