Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Carbon in Boreal Streams: Isotopic Tracing of Terrestrial Sources
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.ORCID iD: 0000-0002-9113-8915
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The boreal biome comprises vast areas of coniferous forests, dotted with millions of peatlands. Plants harbouring these ecosystems fix CO2 from the atmosphere, which is later incorporated into the vegetation biomass and subsequently buried in soils. Over the course of millennia, this process has led to the formation of a large repository of organic C, currently stored in boreal soils. Streams draining this landscape are typically enriched with carbon dioxide (CO2), methane (CH4) and dissolved organic carbon (DOC). As a consequence, streams tend to emit CO2 and CH4 to the atmosphere, two potent greenhouse gases, and thus contribute positively to radiative climate forcing. The sources fuelling C to boreal streams are not well understood. This thesis aims to unravel these sources, and promote a better consolidation of terrestrial and aquatic C biogeochemical processes. The work is largely based on stable and radiogenic C isotope characterization of various dissolved C forms in stream and groundwater, within contrasting ecosystem types across Sweden.

This thesis identifies boreal soils as the main source of CO2 in streams. Soil respiration (i.e. biogenic sources) overwhelmingly supply CO2 to streams, leaving only a few exceptions where geogenic CO2 sources were present. An array of biological processes also transform CO2 during its transport from soils to streams. These include; methanogenesis, aquatic DOC mineralization and primary production. The majority of C in boreal streams is sustained by the decomposition of recent photosynthates, with ancient C substrates holding a negligible share of the total C export. While these results suggest that the repository of ancient soil organic C is currently stable, within boreal forests and peatlands, the close connection with recently occurring photosynthesis suggest that forecasted alterations in plant C allocation patterns, driven by climate and land-use changes, will produce a rapid response in stream CO2 emissions. Isotopic characterization of C in stream and groundwater can help reveal these sources and transformation processes, but its interpretation must be made with care.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 64
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1808
National Category
Other Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-381847ISBN: 978-91-513-0654-4 (print)OAI: oai:DiVA.org:uu-381847DiVA, id: diva2:1304911
Public defence
2019-06-14, Hambergsalen, Villavägen 16B, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2019-05-24 Created: 2019-04-15 Last updated: 2019-06-17
List of papers
1. Multiple sources and sinks of dissolved inorganic carbon across Swedish streams, refocusing the lens of stable C isotopes
Open this publication in new window or tab >>Multiple sources and sinks of dissolved inorganic carbon across Swedish streams, refocusing the lens of stable C isotopes
Show others...
2017 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 9158Article in journal (Refereed) Published
Abstract [en]

It is well established that stream dissolved inorganic carbon (DIC) fluxes play a central role in the global C cycle, yet the sources of stream DIC remain to a large extent unresolved. Here, we explore large-scale patterns in delta C-13-DIC from streams across Sweden to separate and further quantify the sources and sinks of stream DIC. We found that stream DIC is governed by a variety of sources and sinks including biogenic and geogenic sources, CO2 evasion, as well as in-stream processes. Although soil respiration was the main source of DIC across all streams, a geogenic DIC influence was identified in the northernmost region. All streams were affected by various degrees of atmospheric CO2 evasion, but residual variance in delta C-13-DIC also indicated a significant influence of in-stream metabolism and anaerobic processes. Due to those multiple sources and sinks, we emphasize that simply quantifying aquatic DIC fluxes will not be sufficient to characterise their role in the global C cycle.

National Category
Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-328530 (URN)10.1038/s41598-017-09049-9 (DOI)000408285200002 ()28831088 (PubMedID)
Funder
Swedish Research Council, 2012-3919Swedish Research Council, 2007-3841Swedish Research Council, 2013-5001Swedish Research Council Formas, 214-2008-202Knut and Alice Wallenberg Foundation
Available from: 2017-08-25 Created: 2017-08-25 Last updated: 2019-04-15Bibliographically approved
2. Stable carbon isotopes reveal soil - stream DIC linkages in contrasting headwater catchments
Open this publication in new window or tab >>Stable carbon isotopes reveal soil - stream DIC linkages in contrasting headwater catchments
Show others...
2018 (English)In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 123, no 1, p. 149-167Article in journal (Refereed) Published
Abstract [en]

Large CO2 evasion to the atmosphere occurs as dissolved inorganic carbon (DIC) is transported from soils to streams. While this physical process has been the focus of multiple studies, less is known about the underlying biogeochemical transformations that accompany this transfer of C from soils to streams. Here we used patterns in stream water and groundwater C-13-DIC values within three headwater catchments with contrasting land cover to identify the sources and processes regulating DIC during its transport. We found that although considerable CO2 evasion occurs as DIC is transported from soils to streams, there were also other processes affecting the DIC pool. Methane production and mixing of C sources, associated with different types and spatial distribution of peat-rich areas within each catchment, had a significant influence on the C-13-DIC values in both soils and streams. These processes represent an additional control on C-13-DIC values and the catchment-scale cycling of DIC across different northern landscape types. The results from this study demonstrate that the transport of DIC from soils to streams results in more than just rapid CO2 evasion to the atmosphere but also represents a channel of C transformation, which questions some of our current conceptualizations of C cycling at the landscape scale. Plain Language Summary Large carbon dioxide emission to the atmosphere occurs as rainwater percolates through soils and into streams. This physical process is important for the global carbon cycle and has been the focus of multiple studies. However, less is known about the underlying processes that accompanies this transfer of carbon dioxide from soils to streams. Here we analyze the stable isotope composition of soil and stream carbon dioxide and demonstrate that methane production and mixing of carbon sources also occur in soils and streams. These processes were linked to different types and configurations of peat-rich areas, for example, bogs, fens, and riparian zones, found within each of the three studied catchments. Our results therefore demonstrate that the export of carbon dioxide from soils to streams not only results in emissions to the atmosphere but also represents a channel of transformation. This questions some of our current conceptualization of the catchment-scale cycling of carbon dioxide.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2018
Keywords
stable C isotopes, carbon dioxide, dissolved inorganic carbon, methane, soil, stream
National Category
Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-337637 (URN)10.1002/2017JG004083 (DOI)000425517800012 ()
Funder
Swedish Research Council, 2012-3919Knut and Alice Wallenberg Foundation
Available from: 2018-01-03 Created: 2018-01-03 Last updated: 2019-04-15Bibliographically approved
3. Aquatic export of young dissolved and gaseous carbon from a pristine boreal fen: Implications for peat carbon stock stability
Open this publication in new window or tab >>Aquatic export of young dissolved and gaseous carbon from a pristine boreal fen: Implications for peat carbon stock stability
Show others...
2017 (English)In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 23, no 12, p. 5523-5536Article in journal (Refereed) Published
Abstract [en]

The stability of northern peatland's carbon (C) store under changing climate is of major concern for the global C cycle. The aquatic export of C from boreal peatlands is recognized as both a critical pathway for the remobilization of peat C stocks as well as a major component of the net ecosystem C balance (NECB). Here, we present a full year characterization of radiocarbon content (14C) of dissolved organic carbon (DOC), carbon dioxide (CO2), and methane (CH4) exported from a boreal peatland catchment coupled with 14C characterization of the catchment's peat profile of the same C species. The age of aquatic C in runoff varied little throughout the year and appeared to be sustained by recently fixed C from the atmosphere (<60 years), despite stream DOC, CO2, and CH4 primarily being sourced from deep peat horizons (2–4 m) near the mire's outlet. In fact, the 14C content of DOC, CO2, and CH4 across the entire peat profile was considerably enriched with postbomb C compared with the solid peat material. Overall, our results demonstrate little to no mobilization of ancient C stocks from this boreal peatland and a relatively large resilience of the source of aquatic C export to forecasted hydroclimatic changes.

National Category
Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-328531 (URN)10.1111/gcb.13815 (DOI)000414969000046 ()28712133 (PubMedID)
Funder
Swedish Research Council, 2012-3919NERC - the Natural Environment Research Council, NRCF010001Knut and Alice Wallenberg Foundation
Available from: 2017-08-25 Created: 2017-08-25 Last updated: 2019-04-15Bibliographically approved
4. Current forest carbon fixation fuels stream CO2 emissions
Open this publication in new window or tab >>Current forest carbon fixation fuels stream CO2 emissions
Show others...
2019 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, article id 1876Article in journal (Refereed) Published
Abstract [en]

Stream CO2 emissions contribute significantly to atmospheric climate forcing. While there are strong indications that groundwater inputs sustain these emissions, the specific biogeochemical pathways and timescales involved in this lateral CO2 export are still obscure. Here, via an extensive radiocarbon (C-14) characterisation of CO2 and DOC in stream water and its groundwater sources in an old-growth boreal forest, we demonstrate that the C-14-CO2 is consistently in tune with the current atmospheric C-14-CO2 level and shows little association with the C-14-DOC in the same waters. Our findings thus indicate that stream CO2 emissions act as a shortcut that returns CO2 recently fixed by the forest vegetation to the atmosphere. Our results expose a positive feedback mechanism within the C budget of forested catchments, where stream CO2 emissions will be highly sensitive to changes in forest C allocation patterns associated with climate and land-use changes.

National Category
Other Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-381845 (URN)10.1038/s41467-019-09922-3 (DOI)000465201500009 ()31015439 (PubMedID)
Funder
Swedish Research Council, 2012-3919Knut and Alice Wallenberg Foundation
Available from: 2019-04-15 Created: 2019-04-15 Last updated: 2019-05-14Bibliographically approved

Open Access in DiVA

fulltext(5506 kB)106 downloads
File information
File name FULLTEXT01.pdfFile size 5506 kBChecksum SHA-512
7a3cd7a9f404190a3393ea0eeb1b74021cb6a7fd4a8256027eb9001f3f7fd06ac60cfad5c5567391cd06133c6b133254258225ccbd138c88f529991dc4d66d25
Type fulltextMimetype application/pdf
Buy this publication >>

Search in DiVA

By author/editor
Campeau, Audrey
By organisation
LUVAL
Other Earth and Related Environmental Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 106 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 297 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf