Fluvial carbon dioxide emission from the Lena River basin during the spring flood

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 pCO(2) 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 km(2), 66% of the Lena's basin), conducted at the peak of the spring flood. The pCO(2) in the Lena (range 400-1400 mu atm) and tributaries (range 400-1600 mu atm) remained generally stable (within ca. 20 %) over the night-day period and across the river channels. The pCO(2) 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 = 4.46md(-1)), we calculated CO2 emission for the main stem and tributaries. Typical fluxes ranged from 1 to 2 gCm(-2) d(-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 km(2)). 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 TgCyr(-1), which is comparable to the DOC and dissolved inorganic carbon (DIC) lateral export to the Arctic Ocean.

Automated summary

Research has found that pCO(2) in tributaries increases with decreasing mean annual temperature and increasing permafrost in permafrost-affected regions of central and eastern Siberia, positively correlated with carbon stock in soil, proportion of deciduous needleleaf forest, and riparian vegetation. Calculations showed that carbon emissions from lotic waters of the Lena watershed are comparable to those in other permafrost-affected rivers in Siberia.