Date of Award

Fall 2026

Abstract

Climate change–driven permafrost thaw is rapidly altering hydrological connectivity in subarctic peatlands, such as Stordalen Mire in Abisko, Sweden. Increased hydrologic connectivity can in turn impact weathering processes and the rate of geochemical fluxes. Stordalen Mire, a discontinuous permafrost peatland ecosystem 200 km north of the Arctic Circle (68°22′ N, 19°03′ E), is experiencing rapid permafrost thaw leading to the conversion of drier, raised permafrost palsas to saturated wetlands including bogs and fens. As permafrost thaws, the hydrologic connectivity of the mire can change, thereby altering groundwater flow paths within the mire. This study investigates spatial variations in strontium (Sr) isotopes (87Sr/86Sr) across Stordalen Mire to assess evolving surface and groundwater interactions in response to thaw. Water samples were taken from streams, thaw ponds, uplands, a chain of lakes and sites across the mire during the 2023, 2024, and 2025 field seasons (June-August) with accompanying vegetation data from field surveys used to identify transitions among land-cover classes (palsa to bog, palsa to fen, bog to fen, or fen to thaw pond). Samples were processed using trace-element clean techniques and analyzed via multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) at the University of New Hampshire. In addition to surface and porewater sampling, sequential leaching of representative bedrock material was used to constrain potential lithologic Sr sources. Relatively radiogenic 87Sr/86Sr values in fens, when considered alongside rock-leachate compositions and previously proposed hydrologic flow paths, are consistent with groundwater influence involving more radiogenic minerals. At the mire scale, these data support the utility of Sr isotopes as an effective tracer of water sources and hydrologic flow paths, ultimately aiding in the identification of areas that may be hydrologically connected. This work provides the means to evaluate the evolution of thawing peatland landscapes and weathering processes at Stordalen Mire in tandem, providing insight into how geochemical fluxes may evolve under continued warming.

Document Type

Master's Thesis

First Advisor

Maria F. Fahnestock

Second Advisor

Julia G. Bryce

Third Advisor

Ruth K. Varner

Department or Program

Earth Sciences

Degree Name

Master of Science

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