Effects of Mechanical Manipulation and Time on Lead Pellet Distribution in Arkansas Wetlands

Lead poisoning occurs when birds forage in habitats containing lead pellets and ingest and store pellets in their digestive systems. Lead pellets have been banned from use in waterfowl hunting in the United States since 1991; however, residual pellets may remain in wetlands and be available to foraging waterfowl. The purpose of this study was to evaluate changes in lead pellet distribution over time and to determine effects of soil disturbance (disking) on the prevalence of lead pellets in surface and subsurface soils of a 423-ha managed wetland in the Mississippi Alluvial Valley of Arkansas. We collected 128 soil core samples at Halowell Waterfowl Rest Area in 2008 as baseline data and compared results with a previous study of lead pellet distribution at the same wetland in 1992. After disking of a portion of the study site in 2008, we collected soil core samples in the same locations as 2008 from disked or undisked portions of the wetland. We used X-rays to detect pellets in soil core samples and then manually sifted through each sample in which a pellet was indicated. We tested for differences in lead pellet distribution between time periods and between treatment (disking) and control plots using chi-square analysis. We found 30 lead pellets in 2008, which did not differ from the number of lead pellets detected in 1992 (χ2 = 0.95, P = 0.33); however, we did find a greater frequency of lead in surface (top 5 cm) soils in 2008 than in 1992 (χ2 = 13.1, P < 0.01). Disking did not affect overall lead pellet frequency (χ2 = 1.32 P = 0.23), although pellet frequency in surface soils was greater in undisked areas (χ2 = 3.29, P < 0.05). While overall lead pellet densities in disked and undisked areas were both above the level considered available to waterfowl, lead pellet density in the upper 5 cm of the soil column was over four times greater in undisked areas (145,587 pellets/ha) compared to disked areas (31,847 pellets/ha). Disking can effectively reduce lead pellet density in wetlands where long-term accumulation of lead pellets has resulted in high concentrations. We recommend additional research evaluate lead pellet concentrations on private wetlands and agricultural fields, especially rice fields, to better assess changes in lead pellet distribution on a landscape scale.

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