Abstract
Based on vertical distribution of the pesticides in a reservoir, quantitative evaluation of pesticides residues originated from paddy field application were investigated in this study. Runoff loadings of herbicides, which were mefenacet, thiobencarb and daimron, into the reservoir were 138g, 29.8g and 54.7g, respectively. The spatial distribution of pesticides in thermally stratified water clearly show that concentrations of the pesticides residues were same levels as in the inlet part of the reservoir. The dominant residues of the pesticides (ca. 50-60%) were present in the middle water layer accompained with temporal distribution in the reservoir. The inflowed mefenacet may be remaining and degrading in the middle layer of R. Reservoir. The average first-order rate constant for mefenacet is 0.003d-1 for the observed period. The results of the study indicate that spatial monitoring as well as periodical monitoring is essential for the accurate evaluation of the pesticide residues in the lake and reservoir water.
