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Variability of dissolved organic carbon and mineral element concentrations in soil pore waters upon permafrost thaw : case study at Eight Mile Lake, Alaska

Tihon, Emeline
(2020)

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Tihon_04911500_2020.pdf
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Details

Supervisors
Sophie Opfergelt
Faculty
Faculté des bioingénieurs
Degree label
Master [120] : bioingénieur en chimie et bioindustries
Abstract
Climate change impacts numerous ecosystems in the world, including the Arctic region where permafrost is thawing. The importance of thawing permafrost is best appreciated when it is realised that it contains twice as much carbon (C) than in the atmosphere. Temperatures in the Arctic increase two to three times faster than elsewhere in the world, and as permafrost thaws, it releases C into the atmosphere leading to a dangerous positive carbon feedback. This remobilisation of C is from land to atmosphere as CO2 and CH4 and from land to ocean as dissolved organic carbon (DOC). However, large uncertainties remain about DOC transport and processing from permafrost soils to the Arctic Ocean. Permafrost degradation is expected to modify mineral-water interactions in soils, thereby changing redox conditions towards more oxic or more anoxic conditions and releasing dissolved mineral elements in higher concentrations. It remains however poorly investigated how abiotic interactions between mineral elements released upon thawing and organic carbon would modulate the remobilisation of C. Some elements such as Fe and Al are known for their affinity for organic carbon in acidic conditions. We studied the distribution of mineral elements (Al, Fe, Si and Ca) concentrations and DOC concentrations in soil pore waters in the context of permafrost thaw at the Eight Mile lake site, Alaska. This site is known for its long-term permafrost degradation. Our results suggest that these elements will play a role in the (non-)stabilisation of DOC for different scenarios of permafrost degradation. The results highlight that (i) Al might bind with DOC at low pH, (ii) the oxic zone of the permafrost soil might play a key role for stabilising DOC with Fe and (iii) water-mineral interaction might release more Ca and Si as permafrost thaws, with the potential for direct or indirect implications for DOC stabilisation.