The slope of phosphorus concentration against discharge of river reversed at the flux of 105,000m3/ day in Kurose River. On the contrary, such a tendency was not found in Minaga River. Under discharge of river of 105,000m3/day the slope of DIP against the discharge was negative. In the cold season (October to April), its negative slope increased, while it decreased in the hot season (May to September). On the other hand, the correlation coefficient of POP with discharge of river was high in the

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... cold season, while it remarkedly decreased in the hot season. As a reason, it is considered that the mechanisms of sedimentation, formation of particles and so on are complicatedly entangled in the river. Upon discharge of river of 105,000m3/day which corresponds to the rainy season, POP and its slope against discharge of river were high in comparison with DIP and DOP, suggesting the important role of particle for the phosphorus transport. POP increased with an increase in discharge of river during the rainy season. However, the content of phosphorus in particle was highest at the first flush of rain and rather than decreased with discharge of river .