Summary

Description

Lake Lowell is located on Deer Flat National Wildlife Refuge Refuge in Southwest Idaho, in Canyon County. Inflows to the reservoir are a combination of diverted Boise River water and irrigation return flows. Several matrices were evaluated for contamination, including sediment, invertebrates, fish, bullfrogs, bird eggs, and bald eagle feathers. Sediment sampling sites were located around the mouth of the New York Canal, which is the primary water supply for Lake Lowell. Chemical analyses included scans for trace elements and organochlorine pesticides OCs. Bird observations indicated consistent nesting chronology from 2001 through 2003 for bald eagles, osprey, and great blue herons. There were two occupied bald eagle nests and one osprey nest on the Refuge each year during our study. Young were successfully fledged from both eagle nests in 2001. Both eagle nests failed in 2002 and 2003. Young were successfully fledged from the osprey nest and the heron colony each year of our study. Concentrations of inorganic contaminants were generally low in sediment from the Refuge. Boron was the only constituent above background or threshold concentrations cited in the literature, although concentrations were below levels associated with adverse impacts to fish and wildlife. Concentrations of mercury were low in invertebrates and fish, and elevated in some bird eggs. Selenium concentrations in fish species were below the 4 micrograms per gram 1tgg general toxic effects threshold for whole body fish samples, but concentrations exceeded levels associated with mortality in some sensitive species of fish. With the exception of DDE, concentrations of OCs in sediment, fish, and invertebrates did not appear to be at levels harmful to aquatic resources. We made five primary management recommendations based on this study. First, we recommended reviewing the potential mercury sources for Lake Lowell to determine whether inputs are historical or current, and then reducing current inputs where feasible. Second, we recommended additional sampling of mercury concentrations in bald eagles to clarify whether current body burdens were contributing to reproductive impairment. Third, we recommended continued monitoring of the nest success of bald eagles and grebes given their repeated nest failures during this study. Fourth, we provided tissue recommendations for additional testing of selenium concentrations in fish because concentrations appear to be near adverse effects thresholds in sensitive species. Finally, we recommended that managers consider collecting additional information on the likely nature of PCBs present on the refuge, and on the route of exposure for waterbirds.