Abstract
Concentration of the herbicides in water was investigated between 2003 and 2007 at Lake Suwa. Concentration of each herbicide in Lake Suwa was lower than half effective concentration of green algae, so we concluded that these herbicides hardly affected the phytoplankton that lived in Lake Suwa. Herbicides were detected for several months in the lake. When water exchange rate was high in summer due to large amount of rainfall, concentration of herbicides in lake water was reduced.
Concentration and composition of herbicides were different between center of the lake and shore of the lake in 2007. When large amount of herbicides flowed into the lake from rivers, concentration of herbicides at shore of the lake was higher than center of the lake. This result showed that herbicides at the shore of lake were affected by rivers more than center of the lake.
