Abstract
Abstract. Greenhouse gas (GHG) emission from inland waters of permafrost-affected regions is one of the key factors of circumpolar aquatic ecosystem response to climate warming and permafrost thaw. Riverine systems of central and eastern Siberia contribute a significant part of the water and carbon (C) export to the Arctic Ocean, yet their C exchange with the atmosphere remains poorly known due to lack of in situ GHG concentration and emission estimates. Here we present the results of continuous in situ pCO2 measurements over a 2600 km transect of the Lena River main stem and lower reaches of 20 major tributaries (together representing a watershed area of 1 661 000 km2, 66 % of the Lena's basin), conducted at the peak of the spring flood. The pCO2 in the Lena (range 400–1400 µatm) and tributaries (range 400–1600 µatm) remained generally stable (within ca. 20 %) over the night–day period and across the river channels. The pCO2 in tributaries increased northward with mean annual temperature decrease and permafrost increase; this change was positively correlated with C stock in soil, the proportion of deciduous needleleaf forest, and the riparian vegetation. Based on gas transfer coefficients obtained from rivers of the Siberian permafrost zone (k=4.46 m d−1), we calculated CO2 emission for the main stem and tributaries. Typical fluxes ranged from 1 to 2 gCm-2d-1 (>99 % CO2, <1 % CH4), which is comparable with CO2 emission measured in the Kolyma, Yukon, and Mackenzie rivers and permafrost-affected rivers in western Siberia. The areal C emissions from lotic waters of the Lena watershed were quantified by taking into account the total area of permanent and seasonal water of the Lena basin (28 000 km2 ). Assuming 6 months of the year to be an open water period with no emission under ice, the annual C emission from the whole Lena basin is estimated as 8.3±2.5 Tg C yr−1, which is comparable to the DOC and dissolved inorganic carbon (DIC) lateral export to the Arctic Ocean.
Highlights
Climate warming in high latitudes is anticipated to result in mobilization, decomposition, and atmospheric release of significant amounts of carbon (C) stored in permafrost soils, providing a positive feedback (Schuur et al, 2015)
This interest is naturally linked to the Lena River location within the forested continuous permafrost– taiga zone covered by organic-rich yedoma soil
The DOC concentration did not demonstrate any systematic variations over the main stem (10.5±2.4 mg L−1, Fig. 3c); it was higher and more variable in tributaries (15.8 ± 8.6 mg L−1)
Summary
Climate warming in high latitudes is anticipated to result in mobilization, decomposition, and atmospheric release of significant amounts of carbon (C) stored in permafrost soils, providing a positive feedback (Schuur et al, 2015). Over the past 2 decades, there has been an explosive interest to the Lena River hydrology (Yang et al, 2002; Berezovskaya et al, 2005; Smith and Pavelsky, 2008; Ye et al, 2009; Gelfan et al, 2017; Suzuki et al, 2018), organic C (OC) transport (Lara et al, 1998; Raymond et al, 2007; Semiletov et al, 2011; Goncalves-Araujo et al, 2015; Kutscher et al, 2017; Griffin et al, 2018), and general hydrochemistry (Gordeev and Sidorov, 1993; Cauwet and Sidorov, 1996; Huh et al, 1998a, b; Huh and Edmond, 1999; Wu and Huh, 2007; Kuzmin et al, 2009; Pipko et al, 2010; Georgiadi et al, 2019; Juhls et al, 2020), including novel isotopic approaches for nutrients (Si, Sun et al, 2018) and trace metals such as Li (Murphy et al, 2018) and Fe (Hirst et al, 2020) This interest is naturally linked to the Lena River location within the forested continuous permafrost– taiga zone covered by organic-rich yedoma soil. There have been several studies of sediment and particular matter transport by the Lena River to the Laptev Sea (Rachold et al, 1996; Dudarev et al, 2006) together with detailed research of the Lena River delta (Zubrzycki et al, 2013; Siewert et al, 2016)
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