Abstract
During June 1990-December 1991, water samples of the Nogawa River were monthly taken and analyzed for six heavy metallic elements. Concentration of the dissolved heavy metals in the upperstream of the Nogawa River were at the trace levels as: 0.2-8.8μg L-1 for Cu, O.8-17μg L-1 for Zn, 21-513ng L-1 for Pb, 0.2-25ng L-1 for Cd, 6-271 μg L-1 for Fe and 3-45μg L-1 for Mn. However, higher values, especially in the from of total metals (dissolved + particulate), were generally observed in downstream of the river. The removal of dissolved metals by particles during metal transportation in the river and subsequent deposition to the sediment, can explain the decrease in dis- solved metal concentration when the river flows on the gravel and sandy river bed. Significant correlations among flux of heavy metals, especially metals in particulate phase, water flux (Q) and flux of suspended solids (SS) were identified. It is considered that resuspended bottom sediments should predominantly contributed to the increase in flux of heavy metals at rising river stage in dry days.
