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(W/FF226) Ambient Water Toxicity to Daphnia sp. in an Agricultural Watershed in Central Chile . Cooman, Katrien1,2, Gajardo, Marisol1, Barra, Ricardo1, 1 2 ABSTRACT- The first year of a two-year monitoring program has been completed with the aim of investigating water quality of the Chillan River watershed located in central Chile. The watershed has a surface area of 754 km2 and is potentially impacted by intensive agriculture and forestry activities. In three separate surveys, single subsurface grab samples were taken at 17 different sites along the main channel of the river and its tributaries. Samples were chemically analyzed and subjected to standardized toxicity testing with Daphnia magna (introduced species) and Daphnia pulex (native species). Acute and chronic toxicity were detected on both species, with chronic toxicity being higher in tributary samples than in main river samples. Comparing between survey periods, the sampling stations showed more toxicity after strong winter rain events. This increased toxicity could be associated with contaminated runoff. In addition, different sensitivities were observed comparing the two daphnia strains, with the native species being more susceptible to contamination. Toxic samples were filtered by a 0.45 Key words: Watershed, Receiving Water Toxicity, Chile, Daphnia sp. |
m pore size filter and in several cases toxicity was reduced, suggesting that toxicity could be caused either by physical factors or by chemicals adsorbed to particles. The abundant use of pesticides in the region and the chemical analyses performed in the laboratory strongly suggest that toxicity is mainly caused by pesticides (chlorpyrifos and atrazine). In the second year of the monitoring study toxicity characterizations, identifications and confirmations will be performed in order to determine the specific cause(s) of toxicity.