The dynamics of dissolved organic substances in forest catchments and the process of threr export in streams, Hokkaido, Japan.

为了解日本北海道北方森林覆盖的集水区中溶解性有机物质的动态变化，对水溶性物质进行了监测。结果表明：1)调查流域0层水层的通流、干流和渗滤液中含有大量的有机物。然而，大部分流入集水区的有机物质立即被土壤表面吸附，因此它们在溪流中的浓度很低。2)在日本，一般认为清澈的水在森林覆盖的集水区流动。而在针叶林覆盖的蛇形岩流域，水体腐殖质指标E260 （260nm吸收值）高于世界卫生组织（WHO）的标准。这一结果表明，当这种溪流作为饮用水来源时，预处理是必要的，以去除有机物。3)在降雨事件中，大量的溶解有机物被输出到集水区的溪流中。由针叶树凋落物组成的厚O层是溶解有机物的来源。大分子有机酸是森林流域渗滤液中主要的阴离子种类。4)基于总有机碳（TOC）的水文分离表明，一次降雨径流中约有40%为直接径流。由于B层渗滤液中TOC浓度明显降低，可以考虑直接流向O层和A层进入水体。集水区土壤的低渗透性似乎与直接流动的出现有关。这些结果表明，森林有机质对河流水体的污染取决于气候、地表地质、植被等土壤形成因素的条件。

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.