Characterization of dissolved organic matter in deep groundwater by simple analytical methods applicable for small sample volumes

Abstract

The characterization of humic substances in groundwater is usually performed using isolated humic substances from a large volume of groundwater. However, the isolation process requires extensive time and effort, and is not feasible for small-volume samples. In this study, characterization methods available for small-volume ( approximately 1 L ) samples were applied to groundwater and surface water in the Horonobe area, Hokkaido. The methods, 3D- fl uorescence analysis, gel permeation chromatography, and ion chromatography, were used to characterize dissolved organic matter ( DOM ) in the samples, including humic substances. The results indicated that the 3D- fl uorescence spectrum obtained from a small volume of groundwater was similar to that obtained from isolated humic substances and showed little variation with depth. However, the peak position in surface water was di ff erent from that in groundwater. Gel permeation chromatography showed that the DOM in groundwater mainly consisted of humic substances with a molecular weight of approximately 1200–2000 Da, and that the molecular weight decreased with depth. These results are consistent with the characteristics of isolated humic substances. Ion chromatography revealed that organic matter with low molecular weight was a minor component of DOM in the groundwater, which is consistent with gel permeation chromatography results. These results indicate that the methods applied in this study are useful for the characterization of DOM in groundwater using small sample volume.