When Thaw Ponds Start Talking to Groundwater

Takeaway: A thaw pond may look like a puddle, but its climate role depends on whether water is quietly leaking into it, out of it, or both.Tiny Arctic ponds can look like quiet puddles, but they may be part of a much larger climate story. As permafrost thaws, water gathers in sunken ground and forms thermokarst ponds that can release carbon dioxide and methane. This episode follows researchers in Nunavik, northern Québec, as they ask a practical question with big implications: are these ponds sealed off by frozen ground, or are they exchanging water with the subsurface below them?We unpack how field teams measured pond water levels, rainfall, evaporation, seepage, groundwater wells, water chemistry, and the natural “fingerprints” of hydrogen and oxygen isotopes. The result is a more complicated, more useful picture: some ponds sitting in silty ground appear to leak water downward, while ponds in sand can rise and fall with groundwater. Those hidden connections matter because water can move carbon into, out of, and through these ponds, changing how scientists estimate greenhouse gas emissions from thawing northern landscapes.Full paper citation: Somera, R., Lemieux, J.-M., Birks, S.J., Fortier, P., Bélanger, A., & Mohammed, A.A. (2025). Quantifying groundwater exchanges in the water balance of small thermokarst ponds: implications for carbon cycling. Journal of Hydrology, 662, 133964. https://doi.org/10.1016/j.jhydrol.2025.133964Disclosure: This Waterlines episode uses AI-generated voices. The script is based on the cited research paper and is written for public science listening, not as a substitute for the paper itself.