TRACE ELEMENT CONCENTRATIONS IN WATER, SEDIMENT AND BIOTA FROM PATHFINDER NATIONAL WILDLIFE REFUGE, NATRONA AND CARBON COUNTIES, WYOMING

Pathfinder National Wildlife Refuge (Pathfinder NWR), located in Natrona and Carbon Counties, is 50 miles southwest of Casper, Wyoming. Pathfinder NWR, established in 1936, is a refuge and breeding area for migratory waterfowl. The refuge initially encompassed the entire Pathfinder Reservoir, an impoundment of the North Platte River. In 1965, the U.S. Fish and Wildlife Service reduced it to four smaller units to allow more intensive management: the Sweetwater Arm, Goose Bay Unit, DeWeese Creek Unit, and the Sage Creek-Platte Unit. We collected water, sediment and biota samples for trace element analyses in May, June and July 1993 from wetlands next to and including Steamboat Lake in the Sweetwater Arm Unit of Pathfinder NWR. High salinity occurs at all ponds (> 30,000 μmho/cm). Sodium is the most abundant cation and carbonates and sulfates are the most abundant anions in these ponds. Hypersaline wetlands (conductivity > 77,000 μmho/cm) can be lethal to waterfowl. Sodium toxicity occurs when sources of freshwater are not available nearby. We did not find any major trace element problems at the Sweetwater Arm Unit of Pathfinder NWR except for arsenic and chromium in brine shrimp. Although elevated, arsenic and chromium concentrations do not appear to pose a threat to aquatic birds. Major cations and anions, specific conductance and total alkalinity are typical of shallow alkaline wetlands in the arid western United States. Waterfowl nesting should not be encouraged at these ponds due to the potential for sodium toxicity in ducklings or goslings. Nesting enhancement measures could be carried out at the southeast ponds closest to the Sweetwater Arm of the reservoir where freshwater is available. Refuge managers should consider water quality analyses at these ponds before intensive management for waterfowl production. The alkaline ponds, however, do provide good nesting habitat for American avocets. USFWS Region 6 Environmental Contaminants Report ii TABLE OF CONTENTS