158-3 Rapid and emergent water quality changes in permafrost underlain catchments driven by permafrost thaw and sulfide mineral oxidation, Yukon Territory, Canada

Session: Redox-Driven Nutrient and Contaminant Dynamics in Terrestrial Systems

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Resource and logistical constraints have led to a consolidation and decline of circumpolar observations over the last several decades despite rapid environmental change. To address concerns related to northern water security, the Tombstone Waters Observatory in central Yukon, Canada was established in 2018 consisting presently of 7 headwater streams along the Dempster Highway between Km 44 and Km 185 that cover representative ecozones and variable geology and permafrost cover with comprehensive hydrometeorological and water chemistry data. In 2024, field observations at one of our sites revealed a 1900 m² area of tundra vegetation that had been killed by emergent acid seepages and coated the stream with ocherous precipitates. Satellite imagery shows an average increase of 200 m² yr^-1 in acid burn area. This seepage, with a pH~3, sulfate ~4.7 g/L and metal (Fe, Al, Ni, Zn) concentrations reaching tens to hundreds of mg/L has notably impacted water quality since 2023; decreasing stream clarity, lowering pH, increasing specific conductance and inter-annual concentrations and fluxes of dissolved sulfate and metals. Regionally, our water chemistry records reveal increases in sulfate concentrations and fluxes and declines in pH in several catchments, with metal concentrations routinely exceeding guidelines for the protection of aquatic life and drinking water quality. Remote sensing suggests that vegetation kills from acidic seepages and stream discoloration has become widespread over the past decade. In this talk, we presented integrated hydrological, water quality and remote sensing data that highlights the links between surface-groundwater interactions, inter-annual climate variability and complex coupled geochemical and hydrological processes. While results strongly suggest sulfide-mineral oxidation in an expanding active layer is degrading water quality, ongoing efforts are aimed to understand the spatial and temporal extent of these changes, specific mechanisms, and long-term implications for water quality and ecosystem health. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5358

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