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Utilization of ancient permafrost carbon in headwaters of Arctic fluvial networks.

Mann PJ, Eglinton TI, McIntyre CP, Zimov N, Davydova A, Vonk JE, Holmes RM, Spencer RG - Nat Commun (2015)

Bottom Line: Northern high-latitude rivers are major conduits of carbon from land to coastal seas and the Arctic Ocean.Microbial demand was supported by progressively younger ((14)C-enriched) carbon downstream through the network, with predominantly modern carbon pools subsidizing microorganisms in large rivers and main-stem waters.Permafrost acts as a significant and preferentially degradable source of bioavailable carbon in Arctic freshwaters, which is likely to increase as permafrost thaw intensifies causing positive climate feedbacks in response to on-going climate change.

View Article: PubMed Central - PubMed

Affiliation: Department of Geography, Northumbria University, Newcastle Upon Tyne NE1 8ST, UK.

ABSTRACT
Northern high-latitude rivers are major conduits of carbon from land to coastal seas and the Arctic Ocean. Arctic warming is promoting terrestrial permafrost thaw and shifting hydrologic flowpaths, leading to fluvial mobilization of ancient carbon stores. Here we describe (14)C and (13)C characteristics of dissolved organic carbon from fluvial networks across the Kolyma River Basin (Siberia), and isotopic changes during bioincubation experiments. Microbial communities utilized ancient carbon (11,300 to >50,000 (14)C years) in permafrost thaw waters and millennial-aged carbon (up to 10,000 (14)C years) across headwater streams. Microbial demand was supported by progressively younger ((14)C-enriched) carbon downstream through the network, with predominantly modern carbon pools subsidizing microorganisms in large rivers and main-stem waters. Permafrost acts as a significant and preferentially degradable source of bioavailable carbon in Arctic freshwaters, which is likely to increase as permafrost thaw intensifies causing positive climate feedbacks in response to on-going climate change.

No MeSH data available.


Downstream Δ14C DOC values.Δ14C values of (a) initial DOC, and (b) utilized DOC supporting microbial demand (DOCloss) during bioincubations. Δ14C values of utilized DOC were calculated as outlined in equation (1) (see Methods). Table 1 displays mean values for initial and utilized DOC across sites and sample numbers for each site type.
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f2: Downstream Δ14C DOC values.Δ14C values of (a) initial DOC, and (b) utilized DOC supporting microbial demand (DOCloss) during bioincubations. Δ14C values of utilized DOC were calculated as outlined in equation (1) (see Methods). Table 1 displays mean values for initial and utilized DOC across sites and sample numbers for each site type.

Mentions: We conducted 81 individual incubation experiments on samples from 19 streams and rivers throughout the Kolyma fluvial network, grouping by stream size and type (Fig. 1; Supplementary Table 1). Thaw streams, directly draining Yedoma outcrops, contained extremely high concentrations of DOC (10,939±1,278 μM) that are highly depleted in 14C (Δ14C−883±41‰; Fig. 2a). A large proportion of thaw stream DOC was utilized by microorganisms (DOCloss) during short-term (28 days, 20 °C) incubations (47±8%), confirming the high bioavailability of permafrost-derived carbon in fluvial systems1924 (Table 1; Supplementary Table 2). Mean DOC concentrations declined moving downstream through the fluvial network, yet proportions of DOCloss were similar (15–21%) among all other stream and river waters (analysis of variance P>0.05, Table 1; Supplementary Table 2). Erosion-impacted streams that receive greater amounts of permafrost soil inputs via mechanical erosion of the stream banks contain 14C-depleted DOC (−214±145‰; Fig. 2a), highlighting the strong potential for thermokarst processes to sporadically deliver aged OC to fluvial networks. By contrast, all other stream and river waters contained modern initial bulk DOC pools (Δ14C>−50‰; Fig. 2a), consistent with the majority of available radiocarbon data for DOC from major Arctic Rivers141518.


Utilization of ancient permafrost carbon in headwaters of Arctic fluvial networks.

Mann PJ, Eglinton TI, McIntyre CP, Zimov N, Davydova A, Vonk JE, Holmes RM, Spencer RG - Nat Commun (2015)

Downstream Δ14C DOC values.Δ14C values of (a) initial DOC, and (b) utilized DOC supporting microbial demand (DOCloss) during bioincubations. Δ14C values of utilized DOC were calculated as outlined in equation (1) (see Methods). Table 1 displays mean values for initial and utilized DOC across sites and sample numbers for each site type.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4525200&req=5

f2: Downstream Δ14C DOC values.Δ14C values of (a) initial DOC, and (b) utilized DOC supporting microbial demand (DOCloss) during bioincubations. Δ14C values of utilized DOC were calculated as outlined in equation (1) (see Methods). Table 1 displays mean values for initial and utilized DOC across sites and sample numbers for each site type.
Mentions: We conducted 81 individual incubation experiments on samples from 19 streams and rivers throughout the Kolyma fluvial network, grouping by stream size and type (Fig. 1; Supplementary Table 1). Thaw streams, directly draining Yedoma outcrops, contained extremely high concentrations of DOC (10,939±1,278 μM) that are highly depleted in 14C (Δ14C−883±41‰; Fig. 2a). A large proportion of thaw stream DOC was utilized by microorganisms (DOCloss) during short-term (28 days, 20 °C) incubations (47±8%), confirming the high bioavailability of permafrost-derived carbon in fluvial systems1924 (Table 1; Supplementary Table 2). Mean DOC concentrations declined moving downstream through the fluvial network, yet proportions of DOCloss were similar (15–21%) among all other stream and river waters (analysis of variance P>0.05, Table 1; Supplementary Table 2). Erosion-impacted streams that receive greater amounts of permafrost soil inputs via mechanical erosion of the stream banks contain 14C-depleted DOC (−214±145‰; Fig. 2a), highlighting the strong potential for thermokarst processes to sporadically deliver aged OC to fluvial networks. By contrast, all other stream and river waters contained modern initial bulk DOC pools (Δ14C>−50‰; Fig. 2a), consistent with the majority of available radiocarbon data for DOC from major Arctic Rivers141518.

Bottom Line: Northern high-latitude rivers are major conduits of carbon from land to coastal seas and the Arctic Ocean.Microbial demand was supported by progressively younger ((14)C-enriched) carbon downstream through the network, with predominantly modern carbon pools subsidizing microorganisms in large rivers and main-stem waters.Permafrost acts as a significant and preferentially degradable source of bioavailable carbon in Arctic freshwaters, which is likely to increase as permafrost thaw intensifies causing positive climate feedbacks in response to on-going climate change.

View Article: PubMed Central - PubMed

Affiliation: Department of Geography, Northumbria University, Newcastle Upon Tyne NE1 8ST, UK.

ABSTRACT
Northern high-latitude rivers are major conduits of carbon from land to coastal seas and the Arctic Ocean. Arctic warming is promoting terrestrial permafrost thaw and shifting hydrologic flowpaths, leading to fluvial mobilization of ancient carbon stores. Here we describe (14)C and (13)C characteristics of dissolved organic carbon from fluvial networks across the Kolyma River Basin (Siberia), and isotopic changes during bioincubation experiments. Microbial communities utilized ancient carbon (11,300 to >50,000 (14)C years) in permafrost thaw waters and millennial-aged carbon (up to 10,000 (14)C years) across headwater streams. Microbial demand was supported by progressively younger ((14)C-enriched) carbon downstream through the network, with predominantly modern carbon pools subsidizing microorganisms in large rivers and main-stem waters. Permafrost acts as a significant and preferentially degradable source of bioavailable carbon in Arctic freshwaters, which is likely to increase as permafrost thaw intensifies causing positive climate feedbacks in response to on-going climate change.

No MeSH data available.