Abstract
The background value of phosphorus in the Kako river watershed was estimated by using both the percentage of different types of strata occuring in the watershed and the average concentrations of phosphorus in rocks from the strata. The background value is 227μg·g-1. The phosphorus concentration of sandy bottom sediment in Kako river corresponded with the mean value of rocks from strata distributed around the sampling stations. The mean value of the phosphorus concentration in sandy bottom sediment (228μg·g-1) also agrees with the background value of phosphorus.
The phosphorus concentration in sandy bottom sediment doesn't seemingly change, even though an artificial phosphorus load flows into the river. On the other hand, the phosphorus concentration of muddy bottom sediment is higher than the background value for phosphorus. This indicates that there is an accumulation of phosphorus in the bottom sediment.
Most of phosphorus in rocks and bottom sediment is I-P(inorganic phosphorus). I-P fractionation was also carried out using a modification of the method of Williams et. al. HCI-P is a major component of I-P in the rocks, and CDB-P is a major form of I-P in the bottom sediment. The results suggest that phosphorus changes its form through a weathering and sedimentation process.
