TY  - JOUR
A1  - Castro‐Morales, K.
A1  - Canning, A.
A1  - Körtzinger, A.
A1  - Göckede, M.
A1  - Küsel, K.
A1  - Overholt, W. A.
A1  - Wichard, T.
A1  - Redlich, S.
A1  - Arzberger, S.
A1  - Kolle, O.
A1  - Zimov, N.
T1  - Effects of Reversal of Water Flow in an Arctic Floodplain River on Fluvial Emissions of CO2 and CH4
Y1  - 2022-01-04
VL  - 127
IS  - 1
JF  - Journal of Geophysical Research: Biogeosciences
DO  - 10.1029/2021JG006485
PB  - 
N2  - When organic matter from thawed permafrost is released, the sources and sinks of greenhouse gases (GHGs), like carbon dioxide (CO2) and methane (CH4) in Arctic rivers will be influenced in the future. However, the temporal variation, environmental controls, and magnitude of the Arctic riverine GHGs are largely unknown. We measured in situ high temporal resolution concentrations of CO2, CH4, and oxygen (O2) in the Ambolikha River in northeast Siberia between late June and early August 2019. During this period, the largely supersaturated riverine CO2 and CH4 concentrations decreased steadily by 90% and 78%, respectively, while the O2 concentrations increased by 22% and were driven by the decreasing water temperature. Estimated gas fluxes indicate that during late June 2019, significant emissions of CO2 and CH4 were sustained, possibly by external terrestrial sources during flooding, or due to lateral exchange with gas‐rich downstream‐flowing water. In July and early August, the river reversed its flow constantly and limited the water exchange at the site. The composition of dissolved organic matter and microbial communities analyzed in discrete samples also revealed a temporal shift. Furthermore, the cumulative total riverine CO2 emissions (36.8 gC‐CO2 m−2) were nearly five times lower than the CO2 uptake at the adjacent floodplain. Emissions of riverine CH4 (0.21 gC‐CH4 m−2) were 16 times lower than the floodplain CH4 emissions. Our study revealed that the hydraulic connectivity with the land in the late freshet, and reversing flow directions in Arctic streams in summer, regulate riverine carbon replenishment and emissions.
N2  - Plain Language Summary: When the snow and ice melt in the Arctic, then organic matter, carbon dioxide (CO2), and methane (CH4) can be transported from land into rivers. Bacteria or sunlight transform river organic matter, releasing more of those gases. However, little is known about how CO2 and CH4 levels in Arctic rivers change over time or how environmental factors affect them. We measured CO2, CH4, and oxygen in the Ambolikha River in northeast Siberia, from late June to early August 2019. Riverine CO2 and CH4 concentrations decreased over time but remained high enough to be emitted into the atmosphere. Riverine CO2 emissions were five times lower than floodplain terrestrial plant CO2 uptake. Riverine CH4 emissions were 16 times lower than floodplain emissions. Upstream fluvial contributions and lateral influences from the floodplain, must have maintained high riverine gas concentrations during flooding. The direction of the river's flow reversed repeatedly in July and early August, limiting water and gas exchange. Changes in river flow patterns and permafrost thaw must be considered to better quantify temporal and spatial variations in Arctic riverine CO2 and CH4 emissions. This will help us understand the role of Arctic aquatic ecosystems in regional and global carbon budgets.
N2  - Key Points: Elevated concentration and fluxes of carbon dioxide and methane in Ambolikha River decrease from the late freshet to summer. Total floodplain methane emissions were higher than the methane emitted from Ambolikha River. Hydraulic connectivity and river flow reversals in Arctic streams can affect C replenishment and emissions.
UR  - http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/9811
ER  -