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

• Published in: Biogeosciences
• Main Authors: Francis, Adam, Ganeshram, Raja S., Tuerena, Robyn E., Spencer, Robert G. M., Holmes, Robert M., Rogers, Jennifer A., Mahaffey, Claire
• Format: Text
• Language: English
• Published: 2023
• Subjects: Arctic; Arctic Ocean; Kolyma; Climate change; kolyma river; ob river; permafrost
• Online Access: https://doi.org/10.5194/bg-20-365-2023; https://bg.copernicus.org/articles/20/365/2023/

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 utilized dissolved nitrogen species (nitrate and dissolved organic nitrogen (DON)) along with nitrogen isotope values ( δ 15 N-NO <math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="53e1f98be2cdf70dbe180d95894fc6b5"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-20-365-2023-ie00001.svg" width="9pt" height="16pt" src="bg-20-365-2023-ie00001.png"/></svg:svg> and δ 15 N-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 δ 15 N 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 15 N 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 ...