DYNAMICS OF COLLOIDAL PHOSPHORUS IN RIVER WATER

Dynamics of colloidal phosphorus (colloidal-P) in river water after the Tokai Heavy Rainfall was investigated in the Yahagi River. The highest concentration of colloidal-P was observed one week after the Tokai Heavy Rainfall in which colloidal-P accounted for almost 80% of dissolved total phosphorus (DTP). Only at this period, the colloidal-P concentration exceeded that of molybdate reactive phosphorus (MRP), and it means a significant amount of phosphorus in colloidal fraction was eroded from the soil. Colloidal-P concentration was 12.4% of DTP in average during the observation period (from Jun. 2000 to Jul. 2002). The yearly load of colloidal-P from Jun. 2000 to Jun. 2001 (including Tokai Heavy Rainfall) was 2.65 times greater than the next year. High concentration of colloidal-P was observed over many months after the Tokai Heavy Rainfall, due to the effects of its accompanied events such as landslides, restoration works and soil runoff.