@article {2969,
	title = {Heterogeneous Patterns of Aged Organic Carbon Export Driven by Hydrologic Flow Paths, Soil Texture, Fire, and Thaw in Discontinuous Permafrost Headwaters},
	journal = {Global Biogeochemical Cycles},
	volume = {36},
	year = {2022},
	month = {Jan-04-2022},
	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 Δ14C-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. In high latitude environments, soils that have been frozen for millennia are thawing, releasing organic carbon (OC). Thawing and export of OC to downstream aquatic ecosystems is a potential biogeochemical feedback that may accelerate climate warming if large amounts of ancient OC are transformed and released to the atmosphere as greenhouse gases. The magnitude and timing of ancient OC thaw and mobilization are not well defined, so predicting these patterns at local to global scales is challenging. Using a suite of diverse headwater catchments in the discontinuous permafrost zone of Alaska, USA, we identify the main controls on the mobilization of ancient OC from thawing landscapes into adjacent streams. Our surveys show that ancient OC export depends on the complex interaction between fire history, soil type and thawing characteristics, and seasonal warming. We find that all of these factors play a role, resulting in highly heterogeneous release of ancient OC to headwater streams. Aged dissolved organic carbon (DOC) in headwater streams in interior Alaska is heterogeneous across permafrost landscapes indicating the interplay of multiple drivers Aged DOC concentrations increase from spring to fall and are highest in catchments with >50\% burned extent and dominated by silty uplands Aged DOC is proportional to stream solute loads, indicating that deeper flow paths deliver permafrost C to streams Aged dissolved organic carbon (DOC) in headwater streams in interior Alaska is heterogeneous across permafrost landscapes indicating the interplay of multiple drivers Aged DOC concentrations increase from spring to fall and are highest in catchments with >50\% burned extent and dominated by silty uplands Aged DOC is proportional to stream solute loads, indicating that deeper flow paths deliver permafrost C to streams},
	issn = {0886-6236},
	doi = {10.1029/2021GB007242},
	url = {https://onlinelibrary.wiley.com/doi/10.1029/2021GB007242},
	author = {Koch, Joshua C. and Bogard, Matthew J. and Butman, David E. and Finlay, Kerri and Ebel, Brian and James, Jason and Johnston, Sarah Ellen and Jorgenson, M. Torre and Pastick, Neal J. and Spencer, Robert G. M. and Striegl, Robert and Walvoord, Michelle and Wickland, Kimberly P.}
}
@article {2832,
	title = {Permafrost Hydrology Drives the Assimilation of Old Carbon by Stream Food Webs in the Arctic},
	journal = {Ecosystems},
	volume = {23},
	year = {2020},
	month = {Jan-03-2020},
	pages = {435 - 453},
	abstract = {Permafrost thaw in the Arctic is mobilizing old carbon (C) from soils to aquatic ecosystems and the atmosphere. Little is known, however, about the assimilation of old C by aquatic food webs in Arctic watersheds. Here, we used C isotopes (δ13C, Δ14C) to quantify C assimilation by biota across 12 streams in arctic Alaska. Streams spanned watersheds with varying permafrost hydrology, from ice-poor bedrock to ice-rich loess (that is, yedoma). We measured isotopic content of (1) C sources including dissolved organic C (DOC), dissolved inorganic C (DIC), and soil C, and (2) stream biota, including benthic biofilm and macroinvertebrates, and resident fish species (Arctic Grayling (Thymallus arcticus) and Dolly Varden (Salvelinus malma)). Findings document the assimilation of old C by stream biota, with depleted Δ14C values observed at multiple trophic levels, including benthic biofilm (14C ages = 5255 to 265 years before present (y BP)), macroinvertebrates (4490 y BP to modern), and fish (3195 y BP to modern). Mixing model results indicate that DOC and DIC contribute to benthic biofilm composition, with relative contributions differing across streams draining ice-poor and ice-rich terrain. DOC originates primarily from old terrestrial C sources, including deep peat horizons (39{\textendash}47\%; 530 y BP) and near-surface permafrost (12{\textendash}19\%; 5490 y BP). DOC also accounts for approximately half of fish isotopic composition. Analyses suggest that as the contribution of old C to fish increases, fish growth and nutritional status decline. We anticipate increases in old DOC delivery to streams under projected warming, which may further alter food web function in Arctic watersheds.},
	issn = {1432-9840},
	doi = {10.1007/s10021-019-00413-6},
	url = {https://link.springer.com/article/10.1007\%2Fs10021-019-00413-6},
	author = {O{\textquoteright}Donnell, Jonathan A. and Carey, Michael P. and Koch, Joshua C. and Xu, Xiaomei and Poulin, Brett A. and Walker, Jennifer and Zimmerman, Christian E.}
}
@article {2908,
	title = {Carbon Isotope Concentrations in Stream Food Webs of the Arctic Network National Parks, Alaska, 2014-2016},
	year = {2015},
	publisher = {Alaska Science Center, U.S. Geological Survey},
	abstract = {This dataset includes information on the carbon samples that were collected from organic and mineral soils, streams, algae, invertebrates, and fish in the Arctic Network Parks.},
	doi = {10.5066/P9NAUIQR},
	url = {https://doi.org/10.5066/p9nauiqr},
	author = {Carey, Michael P. and O{\textquoteright}Donnell, Jonathan A. and Koch, Joshua C.}
}
