Groundwater Hydrology in Thermokarst Lakes

  • Project PI: David Barnes
  • Project Student: Bridget Eckhardt
  • Keywords: methane, permafrost, taliks, aquifer, hydrology

The complexity of groundwater flow in discontinuous permafrost regions makes it difficult to estimate groundwater quantity and quality, and poses challenges in contaminated groundwater remediation efforts.

This study seeks to gain a better understanding of groundwater hydrology in the discontinuous permafrost regions of Alaska. Understanding groundwater flow dynamics in these areas will benefit regulatory agencies, as well as communities that rely on clean and safe drinking water resources.


Transport of CH4 through Open Taliks in Discontinuous Permafrost Aquifers

Alaska has become a focal point in our understanding of permafrost carbon sources and sinks and the contribution these sources and sinks have on climate change. Until now, permafrost-related research has mainly focused on the supra (above)-permafrost zone and the fate of nearsurface carbon under a warming climate. The CH4 release from the sub-permafrost environment through open taliks constitutes a newly quantified feedback to the climate system. Recent 3-D imaging of discontinuous permafrost in Interior Alaska (Figure 1) together with preliminary numerical permafrost hydrology modeling suggest that during the past 15,000 years, a disproportionately larger volume of permafrost degraded at the bottom (aided by the groundwater heat flux) compared to its top boundary (Figure 2). The resulting sub-permafrost topography is much more dramatic than the supra-permafrost boundary. An abundance of hollow pockets (50 to 100 m depth) scatter the bottom boundary of permafrost, which makes the top appear relatively smooth with the exception of isolated thermokarst-lake and fluvial taliks (thaw bulbs). A rugged permafrost bottom is proposed to favor gas storage in hollow “pockets”, which can rapidly release large sub (below)-permafrost CH4 stores when an open-talik forms, that connects the sub-permafrost to the supra (above)-permafrost environment. Additionally, flowing groundwater could accelerate thaw therefore enhance CH4 formation and release as pathways develop between pockets of methane and expanding taliks. These pockets that have formed on the bottom of the permafrost layer may be a storage and release mechanism for methane that has yet to be investigated. Ultimately numerical modeling is required to understand the magnitude of these possible CH4 sources. The modeling of these sources requires an understanding of the transport mechanisms bringing CH4 to the lake bottom. This project will be a first step in recognizing these transport mechanisms.