Dr Masakazu Aoyama1
1Hirosaki University, Hirosaki, Japan
Dissolved organic matter (DOM) is a major form of organic matter in the hydrosphere and plays an important role in the transport of trace metals such as iron. A significant portion of the hydrosphere DOM is considered to be leached from the soil. The purpose of this study was to clarify what kind of DOM constituent is leached from soil to hydrosphere by comparing the constituents of soil and lake water DOM samples. Lake DOM samples were prepared from the upstream and downstream lakes of the Iwaki River in the northern part of the Honshu island, Japan, and soil DOM samples were from representative soils of the river basin. For HPLC analysis, the hydrophobic fractions of DOM prepared by adsorption of acidified samples onto DAX‐8 resin were used. For comparison, DAX-8 adsorbed fulvic acids were obtained by alkali extraction from the same soils. The constituents of DAX-8 adsorbed DOM fractions and fulvic acids were analyzed by two-dimensional HPLC using hydrophilic interaction chromatography (HILIC) followed by reverse phase chromatography (RP-HPLC). For the DAX-8 adsorbed fractions of soil and lake water DOM, the proportion of the constituents eluting in the most hydrophobic region upon HILIC was smaller than for soil fulvic acids. Upon RP-HPLC, sharp peaks exhibiting only UV absorption and broad peaks exhibiting featureless spectra with the absorbance decreasing gradually from the UV region to the visible region were eluted for the soil DOM and fulvic acids. In contrast, the lake water DOM mainly had broad peaks, and the number of sharp peaks was smaller than the soil DOM and fulvic acids. It was concluded that the main constituents of the DOM that leached from soil to the hydrosphere were dark-colored organic substances having absorption in the UV and visible regions and were more hydrophobic than soil fulvic acids.
Dr. Masakazu Aoyama is a Professor of Soil Science at the Fuculty of Agriculture and Life Science, Hirosaki University. His current research interest is the molecular compositions of DOM and humic substances in soil and aquatic environments. He has been developing chromatographic methods for the analysis of DOM and humic substances.