Does Large Herbivore Activity influence Mercury levels in Arctic Soils?
Mercury (Hg), a neurotoxic pollutant of global significance, is stored in high amounts in Arctic grounds, while its deposition in the Arctic further increases. With climate change inducing accelerated permafrost thaw as well as shortened freezing seasons in seasonal frozen ground, this could lead to the rerelease of Hg into the environment. For this reason, this study addressed the question of whether differences in activity by large herbivores might correlate with differences in soil mercury content in Arctic ground, due to the ground-cooling effects attributed to the animals. Therefore, soil cores from north-eastern Siberia (permafrost soil) and northern Finland (seasonally frozen soil) from sites with different grazing intensities were analyzed and compared for their mercury concentration. Additionally, depth trends of the cores regarding their mercury content, as well as possible correlations with other variables (total organic carbon, absolute water content and mean grain size) were examined. For a merged data set, grazing intensity did not show a significant correlation with mercury content in the soil, while a decrease with depth was detectable for most cores, which was attributed to decreasing surface influence and the associated input of mercury through the atmosphere, vegetation, animal dung and flooding. Total organic carbon showed the most relevant and highest correlation on the mercury content, due to the adsorbing property of organic matter. A separate consideration of the permafrost ground in Siberia and the seasonally frozen ground in Finland showed clear differences in regard to the influence of herbivore activity. While the animals did not show an effect on the concentration of mercury in seasonally frozen ground, the Siberian permafrost sites showed a clear variation in their mercury concentration between grazed and ungrazed sites. In contrast, a difference between sites with existing grazing but of varying intensity was less pronounced. A cause of this phenomenon was presumed in insufficiently diverse animal density, insufficient sample size, prevailing vegetation, as well as occasional flooding. Nevertheless, the samples from Siberia showed a positive correlation between grazing intensity and mercury, indicating that with higher herbivore activity mercury levels increase and suggesting a more effective fixation of the pollutant in permafrost soil.
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Arctic Land Expeditions > FN-Land_2022_Inari
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