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Heterogeneous Patterns of Aged Organic Carbon Export Driven by Hydrologic Flow Paths, Soil Texture, Fire, and Thaw in Discontinuous Permafrost Headwaters
Author(s) -
Koch Joshua C.,
Bogard Matthew J.,
Butman David E.,
Finlay Kerri,
Ebel Brian,
James Jason,
Johnston Sarah Ellen,
Jorgenson M. Torre,
Pastick Neal J.,
Spencer Robert G. M.,
Striegl Robert,
Walvoord Michelle,
Wickland Kimberly P.
Publication year - 2022
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2021gb007242
Subject(s) - permafrost , thermokarst , dissolved organic carbon , soil water , hydrology (agriculture) , environmental science , streams , snowmelt , soil carbon , total organic carbon , physical geography , snow , geology , soil science , geomorphology , ecology , oceanography , geography , computer network , geotechnical engineering , biology , computer science
Abstract Climate change is thawing and potentially mobilizing vast quantities of organic carbon (OC) previously stored for millennia in permafrost soils of northern circumpolar landscapes. Climate‐driven increases in fire and thermokarst may play a key role in OC mobilization by thawing permafrost and promoting transport of OC. Yet, the extent of OC mobilization and mechanisms controlling terrestrial‐aquatic transfer are unclear. We demonstrate that hydrologic transport of soil dissolved OC (DOC) from the active layer and thawing permafrost to headwater streams is extremely heterogeneous and regulated by the interactions of soils, seasonal thaw, fire, and thermokarst. Repeated sampling of streams in eight headwater catchments of interior Alaska showed that the mean age of DOC for each stream ranges widely from modern to ∼2,000 years B.P. Together, an endmember mixing model and nonlinear, generalized additive models demonstrated that Δ 14 C‐DOC signature (and mean age) increased from spring to fall, and was proportional to hydrologic contributions from a solute‐rich water source, related to presumed deeper flow paths found predominantly in silty catchments. This relationship was correlated with and mediated by catchment properties. Mean DOC ages were older in catchments with >50% burned area, indicating that fire is also an important explanatory variable. These observations underscore the high heterogeneity in aged C export and difficulty of extrapolating estimates of permafrost‐derived DOC export from watersheds to larger scales. Our results provide the foundation for developing a conceptual model of permafrost DOC export necessary for advancing understanding and prediction of land‐water C exchange in changing boreal landscapes.