Fractionation of Dissolved Organic Carbon from the Waters of Lake Biwa and its Inflowing Rivers.

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Dissolved organic carbon (DOC) in Lake Biwa and its four inflowing rivers (forestal, industrial, agricultural and urban with catchment areas) was fractionated using three resin adsorbents into six classes : hydrophobic acids, bases and neutrals ; hydrophilic acids, bases and neutrals. Hydrophobic acids (aquatic humic substances, AHSs) and hydrophilic acids (HiAs) were found to dominate in both lake and rivers. In the lake water, HiAs prevailed over AHSs (AHSs : 25-27%, 0.37-0.41 mg Cl-1; HiAs : 40-48%, 0.58-0.78 mg Cl-1) ; in the river waters, the opposite was observed (AHSs : 37-73%, 0.32-0.71 mg Cl-1 ; HiAs : 23-35%, 0.11-0.45 mg Cl-1). Especially in the forestal area, the contribution of AHSs was greatest among the rivers. The UV absorbance over DOC ratio (UV: DOC) for the lake samples increased in the order of HiAs, lake-water DOC, and AHSs. The UV : DOC ratios of both the lake-water DOC and AHSs isolated from Lake Biwa were similar to those reported as algal-derived, suggesting that a significant portion of the DOC in L. Biwa may be aquagenic and algal-derived. The UV : DOC ratio of the river-water DOC was 60% greater than that of the lake-water DOC. The Pedogenic nature of the river-water DOC was implied. However, the UV : DOC ratio of the AHSs isolated from the rivers was low as compared with those reported. It is of interest that the UV : DOC ratio of the urban-river AHSs was slightly lower than that of the lake.
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