Abstract
Field observation on the supply of sediment and nutrients from Nagura river basin, Ishigaki island, was studied in this paper. They were estimated by measuring water velocity, depth, turbidity, concentrations of carbon, nitrogen and phosphrous, in which the former 3 items were measured continuously for 3 months and the concentrations of latter 3 materials were observed only for rainy days. The result has revealed that the sediment yield from the basin in these 3months is 134 tons, and the specific sediment yield in this basin is 8.3gr/m2 for the 3months. It was found that heavy rains yield nutrients mainly in particulate type. However, sugar cane field yields dissolved nutrients gradually after the rain. The timing of flood and tide is an important factor to control the discharge of sediment and nutrients to the tidal area such as lagoon and river mouth.
