Diel cycles of carbon, nutrient and metal in humic lakes of permafrost peatlands

L S Shirokova; D Payandi-Rolland; A G Lim; R M Manasypov; J Allen; J-L Rols; P Bénézeth; J Karlsson; O S Pokrovsky

doi:10.1016/j.scitotenv.2020.139671

Diel cycles of carbon, nutrient and metal in humic lakes of permafrost peatlands

Sci Total Environ. 2020 Oct 1:737:139671. doi: 10.1016/j.scitotenv.2020.139671. Epub 2020 May 25.

Authors

L S Shirokova¹, D Payandi-Rolland², A G Lim³, R M Manasypov³, J Allen⁴, J-L Rols⁴, P Bénézeth², J Karlsson⁵, O S Pokrovsky⁶

Affiliations

¹ Géosciences Environnement Toulouse, GET - CNRS - IRD - OMP - Université de Toulouse, 14, Avenue Edouard Belin, 31400 Toulouse, France; Institute of Ecological Problems of the North, Russian Academy of Science, 23, Naberezhnaya Sev. Dviny, Arkhangelsk, Russia.
² Géosciences Environnement Toulouse, GET - CNRS - IRD - OMP - Université de Toulouse, 14, Avenue Edouard Belin, 31400 Toulouse, France.
³ BIO-GEO-CLIM Laboratory, Tomsk State University, 36 Lenina Pr., Tomsk, Russia.
⁴ EcoLab, Université de Toulouse, CNRS, Toulouse, France.
⁵ Climate Impacts Research Centre (CIRC), Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden.
⁶ Géosciences Environnement Toulouse, GET - CNRS - IRD - OMP - Université de Toulouse, 14, Avenue Edouard Belin, 31400 Toulouse, France. Electronic address: oleg.pokrovsky@get.omp.eu.

PMID: 32521361
DOI: 10.1016/j.scitotenv.2020.139671

Abstract

Despite the importance of surface waters of permafrost landscapes in carbon (C) emission and dissolved C and metal storage and export, the majority of available observations in high latitude aquatic systems deal with punctual or seasonal sampling without accounting for diurnal variations in temperature and primary productivity-respiration cycles. Towards providing comprehensive understanding of diel variations in CO₂ emission, organic C and element concentrations in lakes of frozen peatlands, we monitored, each 2 h over 2 days, the water temperature, pH, CO₂ fluxes, CO₂, CH₄, dissolved organic and inorganic carbon (DOC and DIC, respectively), nutrients, carboxylic acids, bacterial number, and major and trace elements in two acidic (pH = 3.6 and 4.0) and humic (DOC = 15 and 35 mg L^-1) thermokarst lakes of discontinuous permafrost zone in Western Siberia. We discovered a factor of 2 to 3 higher CO₂ concentrations and fluxes during the night compared to daytime in the high-DOC lake. The emission fluxes in the low-DOC lake increased from zero to negative values during the day to highly positive values during the end of night and early morning. The methane concentration varied within a factor of 5 without any link to the diurnal cycle. The bulk of dissolved (< 0.45 μm) hydrochemical parameters remained highly stable with ±10% variation in concentration over 2 days of observation (DOC, DIC, SUVA_254nm, carboxylates (formate, oxalate, puryvate and glutarate), Mn, Fe, Al, other trace elements). Concentrations of Si, P, K, Cu varied within ±20% whereas those of Zn and Ni ranged by a factor of 2 to 4 without any link to diurnal pattern. Overall, the impact of diel cycle on CH₄, DOC, nutrient and metal concentration was below 10%. However, neglecting night-time period may underestimate net CO₂ emission by ca. 30 to 50% in small organic-rich thaw ponds and switch the CO₂ exchange from uptake/zero to net emission in larger thermokarst lakes. Given the dominance of large lakes in permafrost regions, the global underestimation of the emission flux may be quite high. As such, monitoring CO₂ concentrations and fluxes in thermokarst lakes during months of extended night time (August to October) is mandatory for assessing the net emissions from lentic waters of frozen peatlands.

Keywords: Carbon dioxide; Emission; Methane; Organic carbon; Peat; Pond; Thermokarst; Trace metal; Warming.