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

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Abstract

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 CH4 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 CH4 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.

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Acknowledgements

The authors acknowledge the help of the Polar Field Services Team and helicopter pilot, Stan Herman, for assistance and support in the field. They also thank the other Polaris 2017 and 2018 participants for field assistance, ideas, and companionship. J.S.D. thanks Laura Jardine for sharing her soil samples (B2, U1, U3, B3) (Ludwig et al. 2017a) and to Jordan Jimmie for stream discharge data and sampling. This work was funded by National Science Foundation awards OCE-1458305 to M.A.C., 1561437 to S.M.N, J.D.S., and R.M.H and 1624927 to S.M.N., P.J.M. and R.M.H. We thank the two reviewers for their constructive comments that improved the quality of this manuscript.

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Contributions

Conceptualization, JSD, MAC, RMH, SMN, JDS and PJM; methodology, JSD, MAC. PJM, and SML; validation, JSD and MAC; formal analysis, JSD, SML, and MP; investigation, JSD, PJM, SML, MP, and PBH; resources, JSD, PBH, MAC, RMH, SMN, JDS and PJM; data curation, JSD, SML, PJM, and MPwriting—original draft preparation, JSD; writing—review and editing, JSD, MAC, PJM, SML, MP, PBH, RMH, SMN, JDS; visualization, JSD; supervision, MAC; project administration, MAC; funding acquisition, MAC, PJM, RMH, SMN, JDS.

Corresponding author

Correspondence to Jessica S. Dabrowski.

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The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

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Responsible Editor: Sujay Kaushal.

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Appendices

Appendix 1: Methane fluxes

See Table 6.

Table 6 The methane concentrations, measured fluxes, and measured gas exchange coefficients for Landing Lake, July 2018

Appendix 2: Uncertainty estimates in the mass balance model

See Table 7.

Table 7 The parameters in the mass balance and the methods for estimating the uncertainty in each parameter

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Dabrowski, J.S., Charette, M.A., Mann, P.J. et al. Using radon to quantify groundwater discharge and methane fluxes to a shallow, tundra lake on the Yukon-Kuskokwim Delta, Alaska. Biogeochemistry 148, 69–89 (2020). https://doi.org/10.1007/s10533-020-00647-w

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  • DOI: https://doi.org/10.1007/s10533-020-00647-w

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