Using a Whole-stream Approach to Quantify Headwater Yedoma DOC Processing Rates in NE Siberia, Russia

Abstract:

Climate warming triggers the release of permafrost organic carbon (OC) via permafrost thaw and erosion, exporting large amounts of terrestrial C to aquatic environments and making previously frozen OC from a range of soil depths available for microbial processing. It is estimated 210-476 Pg C is stored in deep, ice-rich loess-dominated soils referred to as yedoma. Yedoma is extensive in NE Siberia and Alaska, where it underlies an area of over 1,000,000 km² and averages 25 m in thickness. Recent research suggests ancient (Pleistocene-aged) permafrost OC, such as yedoma OC, is rapidly and preferentially utilized by microbial communities in Arctic headwater streams. We utilized a combination of short-term laboratory incubations and a whole-stream approach to examine permafrost-derived dissolved organic carbon (DOC) uptake, processing, and transport rates in a small stream which drains yedoma uplands in Cherskii, NE Siberia. Short-term incubations were conducted on permafrost leachates mixed with stream water to quantify microbial processing rates of permafrost-derived DOC from leachates made with surface (0-15 cm), shallow (70-100 cm), and deep (<2 m) yedoma sediments. In addition, we conducted whole-stream DOC release experiments to quantify permafrost DOC uptake length, rate, and velocity. DOC composition from samples collected during both the incubations and the nutrient-release experiments was characterized using absorbance measurements (SUVA₂₅₄ and S_R) and florescence spectrometry (EEMs) to quantify how DOC composition correlates to and changes with permafrost DOC bioavailability and processing parameters. Preliminary results suggest DOC processing rates may be highest in leachates made from surface sediments, which receive fresh OC input from modern ecosystems, and from deep sediments, which contain ancient, previously immobile OC. Shallow permafrost OC, which experiences degradation from annual freeze-thaw cycles without receiving fresh OC input, may have the lowest DOC processing rates.