Behavior of Humic Substances and Algal Dissolved Organic Matter as Precursors of Trihalomethane in Lake Biwa

Dissolved organic matter (DOM) in a water sample from Lake Biwa was fractionated with a nonionic resin (DAX-8) into hydrophilic DOM (Hi), hydrophobic acids (HoA) and hydrophobic neutral DOM (HoN). The vertical distribution and seasonal changes of DOM and its fractions were evaluated. The concentrations of DOM, HoA and Hi in surface water samples from Lake Biwa tended to be high in the summer and low in the winter. In the summer, the concentrations of DOM, HoA and Hi varied greatly in the lake thermocline (depth 10∼20 m). The increase in the concentrations of DOM, HoA and Hi in Lake Biwa during the warm season may be attributed to algal DOM. The trihalomethane (THM) formation potential of water samples collected from Lake Biwa was high at a depth of 10 m and 35∼40 μg L−1 at depths lower than 20 m. The THM formation potential per organic carbon unit of algal DOM was larger than that of soil humic substances, and its order was as follows : Microcystis aeruginosa>Cryptomonas ovata>Staurastrum dorcidentiferum.