Effects of Pesticides on Community Productivity of Periphyton

The effects of pesticides on the biomass and community productivity of periphyton were investigated for three years (2001-2003) in Hiroi stream. The biomass of periphyton was affected by the flow of the stream and precipitation. Pesticides, however, showed no effect on the species composition or biomass of periphyton during the study period. Thus, we measured the net community productivity (NCP) and community respiration (CR) rate of periphyton in June and August of 2003. The NCPs in June and August were 64 and 105 mgC · m-2 · h-1 and the CR rates were 74 and 18 mgC · m-2 · h-1, respectively. In June, the main herbicide was detected simetryn, and the insecticide Trichlorfon (DEP) and the fungicide Tricyclazole were detected in August. The lower NCP in June than in August might have been caused by the high concentration of simetryn (>5μg · l-1). However, the NCP was higher in August than in June because DEP and Tricyclazole decreased the respiration rate of organisms such as insects and bacteria. Simetryn reduced NCP, and DEP and Tricyclazole lowered CR level, resulting in an increased NCP. We suggest that measuring the NCP and CR rate of periphyton in aquatic ecosystems is an effective method of assessing the effects of pesticides.