Characteristics of Organic Matter in Rivers Flowing into Lake Kojima, Japan

Water samples were collected from 24 monitoring points in three rivers, Sasagase, Kurashiki and Kamo Rivers, flowing into L. Kojima, Japan bimonthly, from February 2001 to December 2002. Chemical oxygen demand (COD sub(Mn)) was measured in each sample and/or filtrate. The COD sub(Mn) of the sample (t-COD) was used as an index of total organic matter and that of the filtrate (d-COD) was used as an index for dissolved organic matter (DOM). The difference (p- COD) between t-COD and d-COD was used for determining particulate organic matter. Approximately 80 % of t-COD was d-COD as an average of the entire monitoring point. Each d-COD was closely related to the intensity of the fluorescence peak that appeared at EX 300-350 nm/EM 400-450 nm in the fluorescence excitation matrix (EEM). Therefore, the main component of DOM seemed to be fulvic. However, it was suggested that the EEM spectra of the point affected by domestic wastewater was associated with fluorescence whitening agents. On the other hand, p-COD was related to the concentration of chlorophyll a, and was higher at the point having occasionally long residence time. Therefore, each monitoring point had its particular factor for an enhancing t-COD.