Abstract:Abstract. Large amounts of methane (CH4) could potentially be formed as a result of the gradual or abrupt thawing of Arctic permafrost due to global warming. Upon its release, this potent greenhouse gas can be emitted into the atmosphere, or transported laterally into aquatic ecosystems via hydrologic connectivity at surface or groundwaters. While high northern latitudes contribute up to 5 % of total global CH4 emissions, the specific contribution of Arctic rivers and streams is largely unknown. In this study,… Show more
Abstract. Large amounts of methane (CH4) could be released as a result of the
gradual or abrupt thawing of Arctic permafrost due to global warming. Once
available, this potent greenhouse gas is emitted into the atmosphere or
transported laterally into aquatic ecosystems via hydrologic connectivity at
the surface or via groundwaters. While high northern latitudes contribute up
to 5 % of total global CH4 emissions, the specific contribution of
Arctic rivers and streams is largely unknown. We analyzed high-resolution
continuous CH4 concentrations measured between 15 and 17 June 2019
(late freshet) in a ∼120 km transect of the Kolyma River in
northeast Siberia. The average partial pressure of CH4
(pCH4) in
tributaries (66.8–206.8 µatm) was 2–7 times higher than in the
main river channel (28.3 µatm). In the main channel, CH4 was up
to 1600 % supersaturated with respect to atmospheric equilibrium. Key
sites along the riverbank and at tributary confluences accounted for 10 %
of the navigated transect and had the highest pCH4 (41 ± 7 µatm) and CH4 emissions (0.03 ± 0.004 mmolm-2d-1)
compared to other sites in the main channel, contributing between 14 % to 17 % of the total CH4 flux in the transect. These key sites were
characterized by warm waters (T>14.5 ∘C) and low
specific conductivities (κ<88 µS cm−1). The
distribution of CH4 in the river could be linked statistically to T and
κ of the water and to their proximity to the shore z, and these
parameters served as predictors of CH4 concentrations in unsampled
river areas. The abundance of CH4-consuming bacteria and
CH4-producing archaea in the river was similar to those previously
detected in nearby soils and was also strongly correlated to T and κ. These findings imply that the source of riverine CH4 is closely
related with sites near land. The average total CH4 flux density in the
river section was 0.02 ± 0.006 mmolm-2d-1, equivalent to an
annual CH4 flux of 1.24×107 g CH4 yr−1 emitted during a 146 d open water season. Our study highlights the
importance of high-resolution continuous CH4 measurements in Arctic
rivers for identifying spatial and temporal variations, as well as providing
a glimpse of the magnitude of riverine CH4 emissions in the Arctic and
their potential relevance to regional CH4 budgets.
Abstract. Large amounts of methane (CH4) could be released as a result of the
gradual or abrupt thawing of Arctic permafrost due to global warming. Once
available, this potent greenhouse gas is emitted into the atmosphere or
transported laterally into aquatic ecosystems via hydrologic connectivity at
the surface or via groundwaters. While high northern latitudes contribute up
to 5 % of total global CH4 emissions, the specific contribution of
Arctic rivers and streams is largely unknown. We analyzed high-resolution
continuous CH4 concentrations measured between 15 and 17 June 2019
(late freshet) in a ∼120 km transect of the Kolyma River in
northeast Siberia. The average partial pressure of CH4
(pCH4) in
tributaries (66.8–206.8 µatm) was 2–7 times higher than in the
main river channel (28.3 µatm). In the main channel, CH4 was up
to 1600 % supersaturated with respect to atmospheric equilibrium. Key
sites along the riverbank and at tributary confluences accounted for 10 %
of the navigated transect and had the highest pCH4 (41 ± 7 µatm) and CH4 emissions (0.03 ± 0.004 mmolm-2d-1)
compared to other sites in the main channel, contributing between 14 % to 17 % of the total CH4 flux in the transect. These key sites were
characterized by warm waters (T>14.5 ∘C) and low
specific conductivities (κ<88 µS cm−1). The
distribution of CH4 in the river could be linked statistically to T and
κ of the water and to their proximity to the shore z, and these
parameters served as predictors of CH4 concentrations in unsampled
river areas. The abundance of CH4-consuming bacteria and
CH4-producing archaea in the river was similar to those previously
detected in nearby soils and was also strongly correlated to T and κ. These findings imply that the source of riverine CH4 is closely
related with sites near land. The average total CH4 flux density in the
river section was 0.02 ± 0.006 mmolm-2d-1, equivalent to an
annual CH4 flux of 1.24×107 g CH4 yr−1 emitted during a 146 d open water season. Our study highlights the
importance of high-resolution continuous CH4 measurements in Arctic
rivers for identifying spatial and temporal variations, as well as providing
a glimpse of the magnitude of riverine CH4 emissions in the Arctic and
their potential relevance to regional CH4 budgets.
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