Permafrost promotes warmer headwater streams
The presence of permafrost influences groundwater flow through soils, and as a result, can determine stream flow and temperature. Thawing of permafrost may therefore dramatically alter the hydrology of Arctic watersheds. While many research advances have been made in recent years, the hydrology of thawing permafrost terrain is complicated and difficult to measure and observe.
In a new study published in Water Resources Research, a team led by CENPERM researcher Ylva Sjöberg combined field observations with modeling to explore how permafrost governs the relationship between groundwater flow and stream temperature. The authors monitored temperature across 11 headwater streams in Noatak National Preserve in northwest Alaska. To their surprise, summer stream temperatures were warmer in watersheds with more permafrost near the ground surface.
To better understand the reasons for this observation, the authors used a model to simulate the depth and temperature of groundwater flowing along Arctic hillslopes with different permafrost properties. The model results showed that along hillslope with continuous permafrost coverage, groundwater flows mainly through relatively warm, shallow soil horizons. Along hillslopes with no permafrost, groundwater flows through deeper, colder soil horizons prior to entering the stream. Overall, this study suggests that as permafrost thaws, stream water temperatures in the summer may become cooler due to these shifts in groundwater flow. This finding has important implications for stream biota, including fish, which are very sensitive to changing temperatures in the Arctic.
This work is a joint effort between CENPERM and the US Geological Survey Alaska Science Center, the US National Park Service, and the US Department of Energy Oak Ridge National Laboratory. The work takes place in the Arctic Network Parks in Alaska because they lie in a region that is rapidly warming. The research team focuses on headwater streams because these are more susceptible to hydrologic changes than larger rivers, control the flux of solutes and nutrients from the land to rivers and the ocean, and provide critical habitat and food resources to juvenile fish.
Sjöberg, Y., Jan, A., Painter, S. L., Coon, E. T., Carey, M. P., O'Donnell, J. A., Koch, J.C. (2020). Permafrost promotes shallow groundwater flow and warmer headwater streams. Water Resources Research, 56, e2020WR027463, doi: 10.1029/2020WR027463.
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