Abstract
Paddy fields are frequently expected to act as sediment ponds that will counteract the red soil runoff. We observed the suspended sediment budget of paddy fields in six rainfall-runoff events on Ishigaki Island in southwestern Japan. The following facts were noted. 1) Suspended sediment runoff from the paddy fields continued for 6 hours or more after rainfall; 2) a relatively large fraction (soil particle size of around 0.1mm) in turbid water flowing into the paddy fields was deposited there; 3) the abundant fine fraction (soil particle size of around 0.03mm) become newly suspended in the paddy fields and was then discharged; 4) the paddy fields acted as a source of suspended sediment, not as a sink; and 5) the net suspended sediment load tended to increase with increased rainfall.
