Fate and Transport of Rare Earth Elements (REEs) in Arctic Watersheds in Alaska

The distribution and concentrations of rare earth elements (REEs) in soils can be important controls on REE sourcing for transport to surface waters, where their ecological impacts are not wholly understood. Previous studies have recognized the importance of parent material and soil texture associations on soil REE concentrations and transport, but few studies have addressed the fate of REE distributions in permafrost, were unique thermal and hydrological conditions influence soil weathering and transport processes. Seasonal freeze-thaw cycles coupled to the pedogenic forces specific to Arctic environments create uncertainty for the controls on REE distributions and transport in permafrost environments. Further uncertainty arises with the potential for enhanced permafrost degradation, which is expected to increase mineral weathering and amplify REE transport to Arctic surface waters where they can bioaccumulate in Arctic biota and discharge to the marine environment. In order to evaluate potential REE transport and distribution mechanisms in permafrost, this study compares soil REE concentrations to active layer thickness, stream and soil pore water REE concentrations, surficial geology, and catchment chemistry. Soils from three sites in the Arctic Foothills of Alaska were analyzed for solid REE concentration with inductively coupled plasma-mass spectrometry (ICP-MS) to compare vertical distributions with soil properties. Active layer thaw was continuously monitored with buried temperature sensors to compare vertical REE distribution with weathering and reduction-oxidation (redox) zones governed by permafrost thermal processes. These data are discussed in relevance to potential mechanisms for stream loading and translocation in permafrost environments. Finally, relationships between REE distribution both spatially at the landscape scale and vertically at the soil profile are evaluated alongside parent material source and history to offer insight to long-term weathering and accumulation of REEs in permafrost soils.