B123-02
Factors influencing hydrogeochemistry in two permafrost watersheds in the Seward Peninsula, Alaska, USA

Wednesday, 16 December 2020: 11:34
Virtual
Emma Lathrop1, Jeffrey M Heikoop1, Nathan Alec Conroy1, Brent D Newman1, Dea Musa1, Cathy Jean Wilson1, Oana Marina1, George Perkins2 and Stan Wullschleger3, (1)Los Alamos National Laboratory, Earth and Environmental Science Division, Los Alamos, NM, United States, (2)Los Alamos National Laboratory, Earth and Environmental Sciences Division, Los Alamos, NM, United States, (3)Oak Ridge National Laboratory, Climate Change Science Institute, Environmental Science Division, Oak Ridge, TN, United States
Recorded Presentation
Abstract:
Carbon storage and release of emissions from degrading permafrost is linked to hydrologic and geochemical conditions in a landscape. The Next Generation Ecosystem Experiments (NGEE) Arctic project aims to improve understanding of the association between permafrost thaw and the carbon cycle. A key challenge is to understand how small watersheds contribute to fluxes of organic carbon and nutrient fluxes observed in large Arctic rivers. We analyzed variations in hydrologic and geochemical data in a discontinuous permafrost watershed (Teller) and continuous permafrost hillslope (Kougarok) at 18 pre-established intensive sampling stations chosen to represent unique environmental characteristics. Water samples were collected using passive wicks (PCAPs), sippers, and macro-rhizons, and analyzed for major geochemical species.

Major drivers of hydrogeochemical variability included vegetation, soil moisture and redox conditions, water-soil interactions, and mineral solubility. At both Teller and Kougarok, elevated concentrations of nitrate were associated with intensive stations with tall willows and alder shrubs. Accumulation of leaf litter from willows and the inputs from nitrogen-fixing alders led to elevated nitrate concentrations in soil pore water from these vegetation communities. In addition, the higher evapotranspiration from shrubs led to lower soil moisture values observed at these stations. Intensive stations with greater soil moisture and more reducing geochemistry had higher concentrations of reducing species such as filtered iron and manganese and lower concentrations of nitrate, consistent with denitrification. Calcium and strontium, two species associated with water-soil interactions and hydrologic transport, increased in concentration further down topographic transects and had the highest concentrations in toe-slope intensive stations.

Small watersheds such as those highlighted in this study are source areas for hydrologic export of particulate organics and solutes to the ocean. Our data highlight the importance of landscape heterogeneity in controlling hydrogeochemistry, and will be used to better understand factors controlling carbon and nutrient cycling in Arctic landscapes and the impact of climate change and permafrost thaw on changes in carbon emissions.

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