OCCURRENCE OF PESTICIDES IN PRAIRIE LAKES IN SASKATCHEWAN IN RELATIONTO DROUGHT AND SALINITY

Prairie lakes are critical breeding, staging, and feeding habitat for a variety of shorebirds and waterfowl, and lower trophic levels in the se habitats could be affected by agricultural pesticides. Following th e severe drought of 1988 in Saskatchewan, concentration of 11 pesticid es were determined in water, sediment, and zooplankton in 10 permanent and nine semipermanent lakes (those lakes that did not have standing water in 1988). The detection frequency for lindane, alpha-HCH, and 2, 4-D in water was 57, 70, and 78%, respectively, with the maximum conce ntration 0.011, 0.004, and 0.43 mu g/L, respectively. Triallate was de tected in 39% of sediment samples and 54% of zooplankton samples at a maximum concentration of 31 and 10.2 mu g/ kg, respectively. When the lakes were grouped by salinity, detection frequencies of these pestici des were significantly higher in brackish lakes, which tended to be se mipermanent (N = 6, mean specific conductance 3100 mu S/cm) than in sa line lakes, which tended to be permanent (N = 6, mean specific conduct ance 60 900 mu S/cm). Other pesticides were detected in <20% of sample s (diclofop-methyl, atrazine, MPCA, dicamba, and bromoxynil) or not at all (trifuralin and picloram). With one exception, pesticide concentr ations in these lakes were below those levels that might be deleteriou s to aquatic Life, suggesting that these pesticides have not affected the food of avifauna at these lakes.