Using radon to quantify groundwater discharge and methane fluxes to a shallow, tundra lake on the Yukon-Kuskokwim Delta, Alaska

• Published in: Biogeochemistry Vol. 148; no. 1; pp. 69 - 89
• Main Authors: Dabrowski, Jessica S., Charette, Matthew A., Mann, Paul J., Ludwig, Sarah M., Natali, Susan M., Holmes, Robert Max, Schade, John D., Powell, Margaret, Henderson, Paul B.
• Format: Journal Article
• Language: English
• Published: Cham Springer Science + Business Media 01.03.2020; Springer International Publishing; Springer Nature B.V
• Subjects: Atmosphere; Biogeosciences; Carbon sources; Discharge; Earth and Environmental Science; Earth Sciences; Ecosystems; Emissions; Environmental Chemistry; Fluxes; Gases; Greenhouse effect; Greenhouse gases; Groundwater; Groundwater discharge; Lakes; Latitude; Life Sciences; Mass balance; Methane; Microorganisms; ORIGINAL PAPERS; Permafrost; Radon; Tracers; Tundra; Arctic region; Radon-222; Methane; Subarctic; Groundwater; Tundra; Wetland
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1007/s10533-020-00647-w

Northern lakes are a source of greenhouse gases to the atmosphere and contribute substantially to the global carbon budget. However, the sources of methane (CH₄) to northern lakes are poorly constrained limiting our ability to the assess impacts of future Arctic change. Here we present measurements of the natural groundwater tracer, radon, and CH₄ in a shallow lake on the Yukon-Kuskokwim Delta, AK and quantify groundwater discharge rates and fluxes of groundwater-derived CH₄. We found that groundwater was significantly enriched (2000%) in radon and CH₄ relative to lake water. Using a mass balance approach, we calculated average groundwater fluxes of 1.2 ± 0.6 and 4.3 ± 2.0 cm day-1, respectively as conservative and upper limit estimates. Groundwater CH 4 fluxes were 7—24 mmol m⁻² -day⁻¹ and significantly exceeded diffusive air–water CH₄ fluxes (1.3–2.3 mmol m⁻² day⁻¹) from the lake to the atmosphere, suggesting that groundwater is an important source of CH 4 to Arctic lakes and may drive observed CH₄ emissions. Isotopic signatures of CH₄ were depleted in groundwaters, consistent with microbial production. Higher methane concentrations in groundwater compared to other high latitude lakes were likely the source of the comparatively higher CH₄ diffusive fluxes, as compared to those reported previously in high latitude lakes. These findings indicate that deltaic lakes across warmer permafrost regions may act as important hotspots for CH₄ release across Arctic landscapes.