Buffer strips and streamwater contamination by atrazine and pyrethroids aerially applied to Eucalyptus nitens plantations

Summary Concentrations of pesticides in streams draining 20 plantations of Eucalyptus nitens in Tasmania were examined in relation to buffer strip width. Atrazine concentrations on the day of spray in streams draining 15 plantations were significantly negatively correlated with riparian buffer strip width hut not buffer quality. Concentrations following the first rain event and one month after spraying were highly positively correlated with day of spray concentrations and were only weakly correlated with other site characteristics. Streams with 30 m buffer strips had median atrazine concentrations less than 20 µg/L at all times and these buffer widths are recommended for minimising short term ecological impact on streams. In streams draining five plantations that were aerially sprayed with the pyrethroids alpha- or Cypermethrin, pyrethroid concentration and short term changes in drift (downstream movement) of stream invertebrates were highly negatively correlated with buffer strip width but with no other variable. Drift of stream invertebrates is recommended as a biomonitor for the contamination of streams with pyrethroids on the day of spray, sensitive down to 0.1 µg/L. Buffer strips of at least 50 m are recommended to minimise mortality of stream invertebrates from pyrethroid spraying.