Toxicity assessment of water from lakes and wetlands receiving irrigation drain water

A method for reconnaissance-level assessments of the potential toxicity of water in lakes and wetlands that receive irrigation drain water is needed. We evaluated a model that predicts toxicity to aquatic organisms due to major ionic composition as a primary means of assessing water quality. The model was used in conjunction with acute toxicity tests and trace element analyses. Mortality of Ceriodaphnia dubia and fathead minnows (Pimephales promelas) observed in acute toxicity tests was 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 was not toxic to test organisms. Six locations had undiluted water that was toxic to C. dubia due to major ionic composition, and two locations had undiluted water that showed toxic effects caused by factors other than elevated levels of major ions. The model for C. dubia seemed to be sufficiently accurate for future application using our approach to assess lakes and wetlands receiving irrigation drain water.