CORRELATION BETWEEN OVERALL PESTICIDE EFFECTS MONITORED BY SHRIMP MORTALITY TEST AND CHANGE IN MACROBENTHIC FAUNA IN A RIVER

The relationship between change in benthic fauna in the Suna River and shrimp mortality in the river water samples (test was conducted two t imes per week from May to September) was investigated to assess the in secticide impact on the benthic community, The river was selected beca use pesticide application had been restricted for a long time in the u pper reaches, while aerial insecticide spraying had been done four tim es on paddy fields in the lower reaches in summer, Species richness an d density of benthos were high at the stations in the upper reaches, H igh shrimp mortality was measured in the water samples collected from a downstream station during the pesticide spraying period, from late J uly to late August, Species richness and density of benthos markedly d ecreased at the stations in the lower reaches in that period, However, several species of chironomids, Cheumatopsyche (Trichoptera), which d emonstrated tremendous insecticide resistance, and Baetis sahoensis (E phemeroptera), which has a high recovery potential, were not affected, even in the insecticide spraying period, The benthic fauna in the low er reaches tended to recover from autumn to spring, although not suffi ciently, It is considered that the temporal recovery of the benthic co mmunity was brought about through recruitment from the benthic communi ty in the 5-km upper reaches, A close correlation was found between th e high mortality of shrimp in the water samples and the deterioration in the benthic fauna in this river which was contaminated with insecti cides during the summer. (C) 1997 Academic Press.