Groundwater Dominates Fluxes of Water and Organic Carbon in a Permafrost Watershed Across Hydrologic States

Abstract: Supra-permafrost aquifers within the active layer are present in the Arctic during summer. Permafrost thawing due to Arctic warming can liberate previously frozen particulate organic matter (POM) in soils to leach into groundwater as dissolved organic carbon (DOC). DOC transport from groundwater to surface water is poorly understood because of the unquantified variability in subsurface properties and hydrological environments. These dynamics must be better characterized because DOC transport to surface waters is critical to predicting the long-term fate of recently thawed carbon in permafrost environments. Here, we quantified groundwater and DOC fluxes based on Darcy’s Law into Imnavait Creek, Alaska, a representative headwater stream of a continuous permafrost watershed. We developed a statistical ensemble approach to model steady-state groundwater flow. We quantified the model prediction uncertainty using statistical sampling of in situ active layer soil hydro-stratigraphy, high-resolution topography data, and DOC data. The predicted groundwater discharge values representing all possible hydrologic conditions towards the end of the thawing season are similar to and span the observed range of Imnavait Creek streamflow. As the Arctic warms and the supra-permafrost aquifer deepens, groundwater flow is expected to increase. This increase is expected to impact river and lake biogeochemical processes by dissolving and mobilizing more soil constituents in continuous permafrost regions. This study highlights how quantifying the uncertainty of hydro-stratigraphical input parameters helps understand and predict supra-permafrost aquifer dynamics and connectivity to aquatic systems using a simple, but scalable, modeling approach.

Recommended citation: Mukherjee, Neelarun and Chen, Jingyi and Neilson, Bethany T. and Kling, George W. and Cardenas, M. Bayani, Groundwater Dominates Fluxes of Water and Organic Carbon in a Permafrost Watershed Across Hydrologic States. Available at SSRN: https://ssrn.com/abstract=4783339 or http://dx.doi.org/10.2139/ssrn.4783339