Preprints
https://doi.org/10.5194/bg-2021-317
https://doi.org/10.5194/bg-2021-317

  13 Dec 2021

13 Dec 2021

Review status: this preprint is currently under review for the journal BG.

Dissolved organic matter characterization in soils and streams in a small coastal low-arctic catchment

Niek Jesse Speetjens1, George Tanski1,2,3, Victoria Martin4, Julia Wagner5, Andreas Richter4, Gustaf Hugelius5, Chris Boucher1, Rachele Lodi6, Christian Knoblauch7, Boris P. Koch8,9, Urban Wünsch10, Hugues Lantuit2, and Jorien E. Vonk1 Niek Jesse Speetjens et al.
  • 1Vrije Universiteit Amsterdam (VUA), Department of Earth Sciences, Earth and Climate Cluster, Amsterdam, 1081 HV Amsterdam, The Netherlands
  • 2Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research, Permafrost Research Unit, 14473 Potsdam, Germany
  • 3Natural Resources Canada, Geological Survey of Canada–Atlantic, B2Y 4A2 Dartmouth, Canada
  • 4University of Vienna (UniVie), Centre for Microbiology and Environmental Systems Science, Div. of Terrestrial Ecosystem Research, 1030 Wien, Austria
  • 5Stockholm University (SU), Department of Physical Geography,106 91 Stockholm, Sweden
  • 6Ca’ Foscari University of Venice (Unive) and National Research Council, Institute of Polar Science (ISP-CNR), 30172 Mestre Venezia, Italy
  • 7Universität Hamburg, Department of Earth Sciences, Institute of Soil Science, 20146 Hamburg, Germany
  • 8Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research, Ecological Chemistry Research Unit, 27570 Bremerhaven, Germany
  • 9University of Applied Sciences, An der Karlstadt 8, 27568 Bremerhaven, Germany
  • 10Technical University of Denmark, National Institute of Aquatic Resources, Section for Oceans and Arctic, 2800 Kgs. Lyngby, Denmark

Abstract. Ongoing climate warming in the western Canadian Arctic is leading to thawing of permafrost soils and subsequent mobilization of its organic matter pool. Part of this mobilized terrestrial organic matter enters the aquatic system as dissolved organic matter (DOM) and is laterally transported from land to sea. Mobilized organic matter is an important source of nutrients for ecosystems as it is available for microbial breakdown, and thus a source of greenhouse gases. We are beginning to understand spatial controls on the release of DOM as well as the quantities and fate of this material in large arctic rivers. Yet, these processes remain systematically understudied in small, high-arctic watersheds, despite the fact that these watersheds experience the strongest warming rates in comparison.

Here, we sampled soil (active layer and permafrost) and water (porewater and stream water) from a small catchment along the Yukon coast, Canada, during the summer of 2018. We assessed the organic carbon (OC) quantity (using dissolved (DOC) and particulate OC (POC) concentrations and soil OC content), quality (δ13C-DOC, optical properties, source-apportionment), and bioavailability (incubations, optical indices such as slope ratio (Sr) and humification index (HIX)) along with stream water properties (T, pH, EC, water isotopes). We classify and compare different landscape units and their soil horizons that differ in microtopography and hydrological connectivity, giving rise to differences in drainage capacity.

Our results show that porewater DOC concentrations and yield reflect drainage patterns and waterlogged conditions in the watershed. DOC yield (in mg DOC g soil OC−1) generally increases with depth but shows a large variability near the transition zone (around the permafrost table). Active layer porewater DOC generally is more labile than permafrost DOC, due to various reasons (heterogeneity, presence of a paleo-active layer, and sampling strategies). Despite these differences, the very long transport times of porewater DOC indicate that substantial processing occurs in soils prior to release into streams. Within the stream, DOC strongly dominates over POC, illustrated by DOC/POC ratios around 50, yet storm events decrease that ratio to around 5. Source-apportionment of stream DOC suggests a contribution of around 50 % from permafrost/deep-active layer OC, which contrasts to patterns observed in large arctic rivers (12 ± 8 % Wild et al., 2019). Our 10-day monitoring period demonstrated temporal DOC patterns on multiple scales (i.e. diurnal patterns, storm-events, and longer-term trend) underlining the need for high-resolution long-term monitoring. First estimates of Black Creek annual DOC (8.2 ± 6.4 t DOC yr−1) and POC (0.21 ± 0.20 t yr−1) export allowed us to make a rough upscaling towards the entire Yukon Coastal Plain (447 ± 313 t DOC yr−1 and 8.95 ± 9.7 t POC yr−1). With raising arctic temperatures, increases in runoff, soil OM leaching, permafrost thawing and primary production are likely to increase the net lateral OC flux. Consequently, altered lateral fluxes may have strong impacts on the arctic aquatic ecosystems and arctic carbon cycling.

Niek Jesse Speetjens et al.

Status: open (until 27 Jan 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-317', Anonymous Referee #1, 18 Jan 2022 reply
  • RC2: 'Comment on bg-2021-317', Anonymous Referee #2, 18 Jan 2022 reply

Niek Jesse Speetjens et al.

Niek Jesse Speetjens et al.

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Short summary
Climate change and warming in the Arctic exceed global averages. As a result, permanently frozen soils (permafrost) which store vast quantities of carbon in the form of dead plant material (organic matter) are thawing. Our study shows that as permafrost landscapes degrade, high concentrations of organic matter are released. Partly, this organic matter is degraded rapidly upon release while another significant fraction enters stream networks and enters the Arctic Ocean.
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