| Hazards of Klamath Basin irrigation drainwater to aquatic resources were studied in 1991 and 1992, with emphasis on Tule Lake and Lower Klamath Lake National Wildlife Refuges (NWRs). Drainwater samples caused static laboratory bioassay toxicity (growth or survival {dollar}>{dollar}20% below controls) in up to 78% of Lemna minor tests, in up to 49% of Xenopus laevis tests, in 17 and 8% of Hyalella azteca and Pimephales promelas tests, respectively, and 0% in Daphnia magna tests. In situ drainwater exposure caused mortality (survival {dollar}>{dollar}20% below references) in {dollar}>{dollar}83% of Pimephales tests, and {dollar}>{dollar}41% of Daphnia and Hyalella tests. The drainwater system was characterized by low DO, high pH, and toxic amounts of un-ionized ammonia. Drainwater nutrients at one return flow site were 2053 ug/L total nitrogen and 283 ug/L total phosphorus, indicating hypereutrophy. Drainwater samples contained low concentrations of nine herbicides and seven insecticides. Methamidophos drift into Tule Lake NWR waterways adjacent to fields was detected in 3 of 12 application spray events monitored, with over-water deposits of up to 23.2% of the crop target application rate. There were no insecticide-related mortalities during in situ Daphnia and mallard (Anas platyrhynchos) bioassays during the spray events, but Daphnia survival was lower (p {dollar}<{dollar} 0.05) in irrigation return-flow drains than in irrigation water delivery canals. Fish and water-column invertebrates inhabiting drainwater were representive of pollution tolerant species assemblages. The aquatic communities monitored retained little of their historic ecological structure. Hydrologic modifications and hypereutrophic water conditions are fundamental problems that are degrading aquatic communities in the Klamath drainwater system. Water quality hazards to endangered castonomid species need to be reduced immediately. Long-term restoration efforts need to reverse the eutrophication process and improve habitat to retain the remaining native aquatic species. Restoration efforts should be assessed by a combination of water chemistry and biomonitors to determine (1) if water quality meets management goals, and (2) if the water system promotes the survival, reproduction, health, and desired population demographics of indicator species. |
