Preprints
https://doi.org/10.5194/egusphere-2022-671
https://doi.org/10.5194/egusphere-2022-671
10 Aug 2022
 | 10 Aug 2022

Permafrost degradation and nitrogen cycling in Arctic rivers: Insights from stable nitrogen isotope studies

Adam Francis, Raja S. Ganeshram, Robyn E. Tuerena, Robert G. M. Spencer, Robert M. Holmes, Jennifer A. Rogers, and Claire Mahaffey

Abstract. Across the Arctic, vast areas of permafrost are being degraded by climate change, which has the potential to release substantial quantities of nutrients, including nitrogen into large Arctic rivers. These rivers heavily influence the biogeochemistry of the Arctic Ocean, so it is important to understand the potential changes to rivers from permafrost degradation. This study utilised dissolved nitrogen species (nitrate and dissolved organic nitrogen (DON)) along with nitrogen isotope values (δ15N-NO3- and δ15N-DON) of samples collected from permafrost sites in the Kolyma River and the six largest Arctic rivers. Large inputs of DON and nitrate with a unique isotopically heavy δ15N signature were documented in the Kolyma, suggesting the occurrence of denitrification and highly invigorated nitrogen cycling in the Yedoma permafrost thaw zones along the Kolyma. We show evidence for permafrost derived DON being recycled to nitrate as it passes through the river, transferring the high 15N signature to nitrate. However, the potential to observe these thaw signals at the mouths of rivers depends on the spatial scale of thaw sites, permafrost degradation and recycling mechanisms. In contrast with the Kolyma, with near 100 % continuous permafrost extent, the Ob’ River, draining large areas of discontinuous and sporadic permafrost, shows large seasonal changes in both nitrate and DON isotopic signatures. During winter months, water percolating through peat soils records isotopically heavy denitrification signals in contrast with the lighter summer values when surface flow dominates. This early year denitrification signal was present to a degree in the Kolyma but the ability to relate seasonal nitrogen signals across Arctic Rivers to permafrost degradation could not be shown with this study. Other large rivers in the Arctic show different seasonal nitrogen trends. Based on nitrogen isotope values, the vast majority of nitrogen fluxes in the Arctic rivers is from fresh DON sourced from surface runoff through organic-rich top-soil and not from permafrost degradation. However, with future permafrost thaw, other Arctic rivers may begin to show nitrogen trends similar to the Ob’. Our study demonstrates that nitrogen inputs from permafrost thaw can be identified through nitrogen isotopes, but only on small spatial scales. Overall, nitrogen isotopes show potential for revealing integrated catchment wide nitrogen cycling processes.

Journal article(s) based on this preprint

24 Jan 2023
| Highlight paper
Permafrost degradation and nitrogen cycling in Arctic rivers: insights from stable nitrogen isotope studies
Adam Francis, Raja S. Ganeshram, Robyn E. Tuerena, Robert G. M. Spencer, Robert M. Holmes, Jennifer A. Rogers, and Claire Mahaffey
Biogeosciences, 20, 365–382, https://doi.org/10.5194/bg-20-365-2023,https://doi.org/10.5194/bg-20-365-2023, 2023
Short summary Co-editor-in-chief

Adam Francis et al.

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-671', Anonymous Referee #1, 08 Sep 2022
    • AC1: 'Reply on RC1', Adam Francis, 14 Nov 2022
  • RC2: 'Comment on egusphere-2022-671', Anonymous Referee #2, 27 Oct 2022
    • AC2: 'Reply on RC2', Adam Francis, 14 Nov 2022

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-671', Anonymous Referee #1, 08 Sep 2022
    • AC1: 'Reply on RC1', Adam Francis, 14 Nov 2022
  • RC2: 'Comment on egusphere-2022-671', Anonymous Referee #2, 27 Oct 2022
    • AC2: 'Reply on RC2', Adam Francis, 14 Nov 2022

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
ED: Publish subject to minor revisions (review by editor) (17 Nov 2022) by Perran Cook
AR by Adam Francis on behalf of the Authors (29 Nov 2022)  Author's response   Author's tracked changes 
EF by Ariane Baumbach (01 Dec 2022)  Manuscript 
ED: Publish as is (14 Dec 2022) by Perran Cook
AR by Adam Francis on behalf of the Authors (21 Dec 2022)  Manuscript 

Journal article(s) based on this preprint

24 Jan 2023
| Highlight paper
Permafrost degradation and nitrogen cycling in Arctic rivers: insights from stable nitrogen isotope studies
Adam Francis, Raja S. Ganeshram, Robyn E. Tuerena, Robert G. M. Spencer, Robert M. Holmes, Jennifer A. Rogers, and Claire Mahaffey
Biogeosciences, 20, 365–382, https://doi.org/10.5194/bg-20-365-2023,https://doi.org/10.5194/bg-20-365-2023, 2023
Short summary Co-editor-in-chief

Adam Francis et al.

Adam Francis et al.

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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

Vast areas of permafrost are being degraded by climate change, which can release substantial quantities of nutrients into rivers and the ocean. This study shows how nitrogen isotopes can be used to determine how climate change affects the fluxes of nitrogen to the Arctic Ocean through permafrost melt.
Short summary
Climate change is causing extensive permafrost degradation and nutrient releases into rivers with great ecological impacts on the Arctic Ocean. We focused on nitrogen (N) release from this degradation and associated cycling using N isotopes, an understudied area. Many N species are released at degradation sites with exchanges between species. N inputs from permafrost degradation and seasonal river nitrogen trends were identified using isotopes, helping to predict climate change impacts.