Isotopic and Chemical Identification of Hydrological Pathways in a Watershed Underlain by Shallow Discontinuous Permafrost
Abstract
Hydrogeochemical field parameters collected from the Seward Peninsula, Alaska, with support from the United States Department of Energy Next Generation Ecosystem Experiment (NGEE) - Arctic, provide insight to the hydrological connectivity that exists within discontinuous permafrost. Chemical and isotopic constraints allow for the identification and classification of hydrological pathways in permafrost as the Arctic responds to climate change. In discontinuous permafrost, there is potential for hydrological pathways to form in the soil active layer, in bedrock, and below/above/through the permafrost. Natural springs located in the regional carbonate-rich schist demonstrate an initially decreasing discharge downstream with the flow increasing further downslope, near permafrost/no-permafrost transition zones. The hydrological pathways within this region are identified by nitrate and isotopic chemistry measurements. In the summer of 2015, the springs exhibited nitrate values of 1 mg/L, which decreased to 0.05 mg/L above the permafrost transition, and then increased to 0.18 mg/L below the transition. Isotopically, the d18O of water and d15N of nitrate values of the stream water remained relatively constant at 14‰ and 4‰ respectively. The d18O of soil pore water, where nitrification occurs, inferred from the d18O of nitrate ranged notably from -11.2‰ to -22.2‰, with lighter values located at spring headwaters and heavier values located downstream of transition zones. Lighter isotopic spring values are consistent with a winter water source while heavier isotopic values downgradient of the transition suggest a seasonal summer water source. Taken together, the above results suggest additional input of water (and nitrate) to the stream from shallow permafrost, indicating that well-developed hydrologic pathways exist within the discontinuous permafrost. Additional isotopic and chemical datasets will be collected this summer to better understand these hydrological pathways.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMGC43E1199A
- Keywords:
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- 0744 Rivers;
- CRYOSPHEREDE: 1621 Cryospheric change;
- GLOBAL CHANGEDE: 1630 Impacts of global change;
- GLOBAL CHANGEDE: 1836 Hydrological cycles and budgets;
- HYDROLOGY