The monitoring of water soluble materials was carried out to clarify the dynamics of dissolved organic substances in the catchments covered by the boreal forests of Hokkaido, Japan. The results obtained were as follows :
1) A large amount of organic substances was included in throughfall, stem flow and leachate from the O horizon of the catchments investigated. Most of organic substances running into the catchments, however, was immidiately adsorbed in the surface of the soil, so that their concentration in the strem water were very low.
2) In japan, it is generally considered that clear water runs in the catchment covered by forests.
In case of serpentine rock catchment covered by coniferous forests (Picea glehnii), however, the value of E260 (the absorvance of 260nm), the index of humic substanses in stream water, was higher than the criterion of World Health Organization (WHO). This result indicates that the pretreatment wasnecessary to remove organics when such a stream water was used as a source of drinkable water.
3) In rain events, considerable amounts of dissolved organic substances was exported to the stream of the catchments. A thick O horizon consist of the litter from coniferous trees was the source of dissolved organic substances. Macro-molecular organic acids were dominant anion species of the leachate from the O horizon of forest catcments.
4) llydrograph separation based on total organic carbon (TOC) indicated that about 40% of runoff in a rain evet was a direct flow. As the concentration of TOC showed pronounced decrease in the leachate from B horizon, the direct flow was considered to run through O and A horizons and into the stream. The low permeability of the soil in the catchments seems to concern with the appearance of direct flow. These results suggest that the pollution of stream water by organic substances from forests depends on the condition of soil formation factors such as climate, surface geology, vegetation.