The Effect of Subsurface Water Flow on Herbicide Concentrations and Loads in the Stream Water

Abstract

The purpose of this study is to evaluate the effect of subsurface water flow on herbicide residues in stream water. Pesticide concentrations and loads were monitored three times in Yasu River and twice in Hino River from May to June 2005. Surface water always flowed and reached to river mouth in Hino River, although infiltration of all of the surface water was observed in some part of the Yasu River channel. Pesticide concentrations returned to the surface streams were < 1/100 lower than that of surface water before infiltration. Possible reason may be the dilution and diffusion with shallow ground water and/or lake water. Runoff coefficient at the end of receiving stream was calculated to 1.0 for Hino River and 0.01 - 0.1 for Yasu River.