Metabolism overrides photo‐oxidation in CO 2 dynamics of Arctic permafrost streams

• Published in: Limnology and Oceanography
• Main Authors: Rocher‐Ros, Gerard, Harms, Tamara K., Sponseller, Ryan A., Väisänen, Maria, Mörth, Carl‐Magnus, Giesler, Reiner
• Other Authors: Biological Interactions Doctoral Programme, Svenska Forskningsrådet Formas, Vetenskapsrådet
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2020
• Subjects: Arctic; Global warming; permafrost
• Online Access: http://dx.doi.org/10.1002/lno.11564; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Flno.11564; https://onlinelibrary.wiley.com/doi/pdf/10.1002/lno.11564; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/lno.11564; https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.1002/lno.11564

Abstract Global warming is enhancing the mobilization of organic carbon (C) from Arctic soils into streams, where it can be mineralized to CO 2 and released to the atmosphere. Abiotic photo‐oxidation might drive C mineralization, but this process has not been quantitatively integrated with biological processes that also influence CO 2 dynamics in aquatic ecosystems. We measured CO 2 concentrations and the isotopic composition of dissolved inorganic C (δ 13 C DIC ) at diel resolution in two Arctic streams, and coupled this with whole‐system metabolism estimates to assess the effect of biotic and abiotic processes on stream C dynamics. CO 2 concentrations consistently decreased from night to day, a pattern counter to the hypothesis that photo‐oxidation is the dominant source of CO 2 . Instead, the observed decrease in CO 2 during daytime was explained by photosynthetic rates, which were strongly correlated with diurnal changes in δ 13 C DIC values. However, on days when modeled photosynthetic rates were near zero, there was still a significant diel change in δ 13 C DIC values, suggesting that metabolic estimates are partly masked by O 2 consumption from photo‐oxidation. Our results suggest that 6–12 mmol CO 2 ‐C m −2 d −1 may be generated from photo‐oxidation, a range that corresponds well to previous laboratory measurements. Moreover, ecosystem respiration rates were 10 times greater than published photo‐oxidation rates for these Arctic streams, and accounted for 33–80% of total CO 2 evasion. Our results suggest that metabolic activity is the dominant process for CO 2 production in Arctic streams. Thus, future aquatic CO 2 emissions may depend on how biotic processes respond to the ongoing environmental change.