TOXICITY ASSESSMENT OF WATER FROM LAKES AND WETLANDS RECEIVING IRRIGATION DRAIN WATER

A method for reconnaissance-level assessments of the potential toxicit y of water in lakes and wetlands that receive irrigation drain water i s needed. We evaluated a model that predicts toxicity to aquatic organ isms due to major ionic composition as a primary means of assessing wa ter quality. The model was used in conjunction with acute toxicity tes ts and trace element analyses. Mortality of Ceriodaphnia dubia and fat head minnows (Pimephales promelas) observed in acute toxicity tests wa s compared to mortality predicted by the model. The method was applied at 22 lakes and wetlands on federally administered lands in Colorado, Montana, Utah, and Wyoming. Fourteen of 22 locations had water that w as nor toxic to test organisms. Six locations had undiluted water that was toxic to C. dubia due to major ionic composition, and two locatio ns had undiluted water that showed toxic effects caused by factors oth er than elevated levels of major ions. The model for C. dubia seemed t o be sufficiently accurate for future application using our approach t o assess lakes and wetlands receiving irrigation drain water.