ICMGP 2022 – On-Demand / Poster Presentation

Abstract Information :

Impacts from invasive earthworms on mercury (Hg) has to date been studied from a mass-balance perspective where earthworms mix mercury rich litter to deeper soil layers. However, earthworms also alter geochemical properties of soils and boost mineralization of soil organic matter and less is known about their effects on Hg speciation and plant uptake. ?Worming? effects have been proven to convert vegetation community from heath to meadow and thus increase plant N availability and greening, even exceeding reported effects of climate warming or nutrient addition. In this study, we investigate how the addition of invasive geoengineering worms to northern soils affect total mercury (THg) and methylmercury (MeHg) concentrations in tundra soils. We used a four-year long experiment with natural soil mesocosms, consisting of two vegetation types (heath and meadow) exposed to two treatments (worms, no worms) to assess impact on Hg forms and plant uptake of Hg. We observed 31% higher THg concentrations (p<0.05) in the O horizon beneath heath vegetation (shrub dominated) compared to meadow vegetation (herb dominated). MeHg concentrations were also found to be significantly higher (about +12%) throughout the upper 0.3 m of the heath soil than in soil under meadow vegetation. However, there was no significant difference for either THg or MeHg due to our earthworm treatment. Nevertheless, heath plant biomass stored larger THg pools (68.3 ?g/mesocosm) than meadow (13.8 ?g/mesocosm) in response to earthworms. We conclude that introducing geoengineering earthworms does not directly affect mercury concentrations in Arctic soils. As a secondary effect, biomass rather incorporates more mercury because of the earthworm?s presence and therefore making it available to grazing animals.