Wetland soil and vegetation bismuth content following experimental deposition of bismuth pellets

Abstract

Bismuth pellets have been approved as a non-toxic alternative to lead pellets in Canada since 1997 but, to our knowledge, there is little literature for soil and vegetation bismuth content in areas of bismuth pellet deposition. The present study addresses this shortcoming by measuring wetland soil and vegetation bismuth content following experimental deposition of bismuth pellets under ambient and experimentally increased acidic deposition conditions. We manipulated 24 plots in a fully factorial design (bismuth shot × soil acidification) in a south-eastern Ontario freshwater wetland during 1999–2003. Soil pH (range 6.5–7.3) increased significantly (p = 0.001) during the experimental period but there were no significant differences amongst treatments (p = 0.79). Significantly (p < 0.05) greater bismuth concentrations were measured in soil receiving bismuth pellets (mean ± SE, n = 6; with acidification = 2.55 ± 1.02 μg Bi g⁻¹ dry mass [DM]; without acidification = 6.40 ± 2.23 μg Bi g⁻¹ DM) compared to plots that were not seeded with bismuth pellets (without acidification = 0.42 ± 0.09 μg Bi g⁻¹ DM; with acidification = 0.39 ± 0.10 μg Bi g⁻¹ DM). Nevertheless, bismuth levels in 20 of 24 aboveground tissue samples from the Carex lacustris–Agrostis scabra community were below detection levels (0.057 μg Bi g⁻¹ DM); the other samples ranged from 0.065 to 0.095 μg Bi g⁻¹ DM, similar to global background levels. Primary productivity in plots receiving bismuth pellets and soil acidification was not significantly (p = 0.15) different to vegetation in plots that were not manipulated. The results suggest bismuth mobilization from bismuth pellets into soil but not to aboveground vegetation.