Humic substances (HS) derived from terristrial area play important roles to supply essential minerals for the growth of aquatic organisms in estuaries. Therefore, the watershed management focusing on the transportation of essential minerals from terrestrial area to estuaries is needed for the conservation of estuarine ecosystem. Although it is said that a part of HS coagulates in estuaries with the increase of salinity, its mechanism has not been well-known. In this study, the coagulation model

more »

... for humic substances in estuaries was developed on the basis of DLVO theory and hydrophobolic interaction which caused a strong attractive force between HS. This attractive force was estimated with hydrophobic index (E254/TOC) of HS and its molecular weight detected by gel chromatography analysis with 254nm spectrophotometer. The developed model could explainthe coagulation mechanism of humic acid according to the decrease of surface potential in estuarine condition. The result of simulation using this model showed that humic acid with intermediate molecular weight around 20kDa easily coagulated at the high salt concentration in estuaries.