FATE AND EFFECTS OF THE HERBICIDE ATRAZINE IN FLOW-THROUGH WETLAND MESOCOSMS

Wetland mesocosms were exposed to increasing concentrations of atrazin e over time at levels typical of midwestern surface waters following s pring runoff(l5 to 75 mu g/L). Atrazine had a half-life of 8 to 14 d i n the 230-m-long wetlands. End points measured included nutrient level s; periphyton biomass; periphyton productivity and respiration; growth of selected macrophytes; and survival and growth of Daphnia magna (15 , 25 mu g/L atrazine), Rana pipiens (15, 25 mu g/L), and Pimephales pr omelas larvae (25 to 75 mu g/L) and adults (50, 75 yg/L). Interaction between nutrient status or grazing intensity and atrazine effects were measured using periphyton enrichment and grazing exclosure experiment s. Only periphyton, Ceratophyllum demersum, Zizania aquatica, and Daph nia were significantly affected by atrazine at any of the concentratio ns tested. Periphyton net productivity was significantly depressed by incubation in treated water as compared to control water at greater th an or equal to 25 mu g/L atrazine (9 to 27-d exposures). In response, dissolved nutrient concentrations increased in treated mesocosms after 14 d. Ceratophyllum length/weight ratios increased after 6-d exposure s to 50 mu g/L atrazine, while Zizania senesced prematurely during tre atments of 50 or 75 mu g/L atrazine (97 d of cumulative exposure). Per iphyton developed resistance to atrazine only at concentrations greate r than or equal to 50 mu g/L. Atrazine effects on periphyton compositi on varied with the N:P supply ratio. Daphnia survival was significantl y depressed at 15 mu g/L atrazine (48-h exposures).