The role of plants and animals in transferring atmospheric mercury deposition within alpine ecosystems

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Clifford R. Adamchak and Hannah R Miller, University of Colorado, Boulder, Boulder, CO, Clifford R. Adamchak and Hannah R Miller, Institute of Arctic and Alpine Research, Eve-Lyn S. Hinckley, Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO

Background/Question/Methods
Mercury (Hg) is a global pollutant that originates from both natural and anthropogenic sources and is currently cycling through air, land, and water systems at levels 3-fold higher than those of the pre-industrial era. Mercury movement into the biosphere persists largely because it is dispersed far distances as nanoparticles of inorganic Hg. Within terrestrial ecosystems, atmospherically deposited Hg may be cycled among vegetation, soils, animal tissues, and hydrological flow paths. Past research has documented long-distance transport of Hg to remote regions far from industrial sources, including disproportionately higher levels in alpine and high latitude systems. However, little is known regarding the mechanisms that underly Hg cycling in the vegetation of high elevation mountain ecosystems or its movement into the food chain. A major concern is the biological transfer of Hg as monomethyl mercury (MMHg), a neurotoxin that bioaccumulates and biomagnifies in successive trophic levels. To better understand the fate of atmospherically deposited Hg in the alpine zone and the role vegetation and animals play in alpine Hg cycling, this study investigated its movement within talus and dry meadow ecosystems of the Niwot Long-term Ecological Research site, Colorado. This presentation provides new data on total Hg (THg) and MMHg in ecosystem pools and a relatively isolated terrestrial food web, including dust, lichen, vegetation, pikas, and weasels.
Results/Conclusions
Measurable THg was found in all sample types. The only significant difference was between atmospheric dry deposition (dust) and the vegetation samples (graminoids and forbs) (p < 0.05). Total Hg concentrations increased in plant litter with decomposition of plant tissues over time, potentially acting as an input to soils and groundwater. Monomethyl mercury was found in high concentrations in the weasels (625 ± 267.47 ng g-1), indicating that animals feeding at higher trophic levels bioaccumulate MMHg in their tissues. However, MMHg concentrations were below detection limits in the dust, vegetation, and pikas, indicating that weasels are getting MMHg from other sources, likely aquatic environments where it can be produced under reducing conditions. This project provides a foundational investigation of ecosystem Hg cycling within an alpine ecosystem and indicates the importance of plants and animals for Hg transfers. It will inform future research both locally and in other alpine areas where atmospheric Hg deposition is an increasing concern.