Effects of paraquat on invertebrates in a Canterbury stream,New Zealand

During 1966 and 1967, paraquat was applied on three occasions at 2 ppm for 30 min to control aquatic weeds in the South Branch experimental stream, a tributary of the lower Waimakariri River, Canterbury, South Island, New Zealand. Effects on the invertebrate fauna of the stream were studied before, during, and after the applications, by Surber and drift‐net samples.

After a heavy initial kill, the paraquat treatment reduced the number of amphipods caught in the drift fauna to 5% of the pre‐treatment level, and there was a slight reduction in the numbers of hemipterans. The total numbers in Surber samples increased markedly a year after treatments ended, mainly due to increased numbers of trichopterans.