Lead Shot Availability to Birds Using the North Platte River near a Trap and Skeet Range

摘要

A trap and skeet shooting range gun club is located on the North Platte River, below the Guernsey Reservoir in Wyoming. In 1999, we obtained sediment samples to determine if lead shot from shooting activities was present and potentially available to waterfowl and bald eagles. We collected 25 sediment samples, each consisting of the upper 10 cm of sediment, every 1.5 meters along transects that paralleled the river bank and skeet range. Sediment was sorted using a series of sieves. Nineteen of the 25 samples contained at least one lead shot (range = 1-14 lead shot/sample). Samples nearest the bank where the range is located contained no shot but as we moved across the river, the number of samples with shot present increased. Clay target fragments also littered the riverbed. In 2003, we intensified our efforts by taking 300 sediment samples as described above, but we also recorded each sample location by GPS and plotted the data using Asset Surveyor to show the distribution and density of lead shot. We analyzed sediment, biofilm, crayfish, and white suckers to determine if lead and other metals were accumulating in the food chain and to assess potential threats to waterfowl and bald eagles feeding from the river. Samples of clay target fragments were also collected and analyzed because the paint of the targets may contain elevated concentrations of some metals, which could leach into the river. Lead shot was present and available to waterfowl but it was not present at a density associated with bird die-offs. We found that clay target fragments and shot were transported downstream and that greater concentrations of arsenic, cadmium, mercury, and selenium were associated with orange-colored clay targets. However, except for selenium concentrations, trace metals including lead were not greatly elevated in sediment and biota. Elevated selenium concentrations in biota were most likely the result of sources upstream. Regulatory concerns associated with the discharge of lead shot and clay targets into a water of the United States are discussed.