Dynamics and trihalomethane formation potential of recalcitrant dissolved organic matter in lake water

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Dissolved organic matter (DOM) in water from eutrophic Lake Kasumigaura, its inflowing rivers, and several other DOM sources in the lake catchment area was fractionated using a long-term biodegradation test and resin adsorbents into ten classes: aquatic humic substances (AHS), hydrophobic neutrals (HoN), hydrophilic acids (HiA), bases (BaS), hydrophilic neutrals (HiN), and recalcitrant AHS, HoN, HiA, BaS, and HiN. The DOM-fraction distribution pattern, the trihalomethane formation potential (THMEP, μmol・mgC^<-1>) and molecular size distribution of the DOM, AHS and the hydrophilic fractions (HiF=HiA+BaS+HiN) were evaluated.DOM-fraction distribution patterns were significantly different depending on the origin of the sample. AHS and HiA ware found to be the dominant fractious in DOM in all samples studied. HiA prevailed over AHS in the lake water, whereas AHS were slightly more abundant than HiA in the river waters. AHS were in the great majority in forest streams and plowed-field percolates. R-DOM fraction distribution patterns clearly indicated that the dominant recalcitrant DOM fraction is HiA not AHS in the lake water, whereas AHS prevailed over HiA in the river-water R-DOM. The THMFP of HiF was found to be comparable to that of AHS in the lake water. The importance of HiF over AHS as a THM precursor became pronounced when THMFP was evaluated in terms of concentration (μmol・L^<-1>). Molecular size distributions all exhibited a narrow size range and relatively low molecular weights. The weight-averaged molecular weights of DOM, AHS and HiF were 780, 960 and 610 g-mole^<-1>, respectively.