Abstract
The runoff behavior characteristics of pesticides were analyzed every three days and five flooding-stage observations were carried out for five months at three traverse points in the Yodo River. The differences in pesticide concentretion among the three traverse points were particularly seen during the flooding-stages. The total runoff loads of pesticides for about five months from late April to late September were larger according to both the regular and flooding-stage observations than according to only the regular observation. The total runoff loads of many pesticides in 2005, which was a dry year, were smaller than in 2004, which was a rainy year and 2001, which had a average amount of rain among the three regular observations. Most pesticide loads estimated using monthly and bimonthly observations in 2005 were smaller than those estimated using observations every three days during the observation period. Those estimated using semimonthly and monthly observations were 0.5- to 2.0-fold those estimated every three days. The change in the DI of a tap water quality standard was found to be less than 0.37 in 2005 according to the every-three-day-observation data and the five-flooding-stage-observation data.
