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The dynamics of non-methane hydrocarbons and other trace gas fluxes at a subarctic mire in northern Sweden

Bäckstrand, Kristina (2004) In Lunds universitets Naturgeografiska institution - Seminarieuppsatser
Dept of Physical Geography and Ecosystem Science
Abstract
In the context of climate change, it is important to understand how the terrestrial carbon cycle is interacting with the anthropogenic increase in atmospheric carbon dioxide (CO2) concentration. Boreal and subarctic regions in the northern hemisphere are great carbon pools, as well as they are subject to predicted warming. These facts place them in the absolute frontline of ecosystems that are to be studied in the context of coupled climate models, where the terrestrial carbon cycle is included. In addition to CO2 and methane (CH4), which have been intensively studied regarding carbon cycle and climate, there are other biogenic volatile organic compounds (BVOC) emitted by vegetation that have shown to be of great importance. One group is... (More)
In the context of climate change, it is important to understand how the terrestrial carbon cycle is interacting with the anthropogenic increase in atmospheric carbon dioxide (CO2) concentration. Boreal and subarctic regions in the northern hemisphere are great carbon pools, as well as they are subject to predicted warming. These facts place them in the absolute frontline of ecosystems that are to be studied in the context of coupled climate models, where the terrestrial carbon cycle is included. In addition to CO2 and methane (CH4), which have been intensively studied regarding carbon cycle and climate, there are other biogenic volatile organic compounds (BVOC) emitted by vegetation that have shown to be of great importance. One group is called non-methane hydrocarbons (NMHCs). Their emissions is a part of the carbon flux in ecosystems, and have an indirect role in determining atmospheric concentration of some greenhouse gases as well as biogenic aerosols. A study of CO2, CH4 and NMHC flux dynamics has been conducted on the subarctic mire Stordalen in northern Sweden. The objective is to contribute to the existing knowledge about exchanges of CO2 and CH4, and primarily to add new knowledge of NMHC emissions from a subarctic ecosystem, which has not earlier been studied.
An automatic multichamber system was used to collect high temporal resolution data of CO2 and total hydrocarbon (THC) fluxes from three different sub-ecosystems on the mire: a wet minerotrophic site, a wet intermediate ombro-minerotrophic site and a semiwet ombrotrophic site. Further, manual sampling of CH4 fluxes was conducted approximately three times a week, from mid-June to late August. This gave the possibility to estimate the amount of NMHCs (THC flux -CH4 flux). A temperature dependent respiration model was developed from night time CO2 flux data, and gross primary production (GPP) could be estimated for each sub-ecosystem. Environmental variables as light, temperature, moisture and thaw depth are included in the correlations.
The results show a certain degree of temperature, light and GPP dependency for NMHC emissions from all of the different plant communities, however it is a great distinction between different plant specie. The largest emissions come from wet minerotrophic sub-ecosystems with vascular plants, compared to a mostly Sphagnum moss vegetated semiwet site, 2.8 mg/m2/hr and 0.9 mg/m2/hr respectively. The NMHC flux rates are however, likely to be underestimated. They are based on the molar weight of CH4 (16 g/mol), while isoprene (C5H8), which is one of the lightest NMHCs, have a molar weight that is more then four times greater. The output of NMHC-carbon from the mire ecosystem was found to be close to 2 % from the wet minerotrophic site, in relationship to CO2-C and CH4-C. CH4 emissions are higher from wet, compared to semiwet microsites. The water table position at a depth of 15-25 cm play an important role at the semiwet site, while water table variations within a depth of 0-10 cm do not affect the CH4 emissions. Moreover, the presence of vascular plants and their ability to give qualitative substrates for CH4 production through photosynthesis, as well as their capacity for plant mediated CH4 transport, are most likely explaining the difference between the two sites. This is in addition to the actual moisture content, explained as being the main cause for high CH4 emissions. Conclusively, research of BVOCs from northern latitude ecosystem like the subarctic mire Stordalen, should be a part in future studies of the terrestrial carbon cycle. Their part in the carbon budget at this site is shown to be significant. (Less)
Abstract (Swedish)
Populärvetenskaplig sammanfattning: Under alla tider har planeten Jorden genomgått en naturlig klimat variation. Utöver denna naturliga variation i klimatet, så har människan, under det senaste århundradet, medverkat till en ökning av växthusgaser i atmosfären. Detta kan innebära att växthuseffekten intensifieras och Jorden bli utsatt för onaturliga temperaturökningar. Koldioxid (CO2), från bland annat förbränning av fossila bränslen, är en av de mest diskuterade och viktigaste växthusgaserna. Förutom att CO2 skapas utifrån mänskliga aktiviteter, så har växthusgasen också ett nära samband med biosfären genom att den upptas genom växternas fotosyntes (produktion) och avges genom växternas respiration (andning). Ett liknande samband mellan... (More)
Populärvetenskaplig sammanfattning: Under alla tider har planeten Jorden genomgått en naturlig klimat variation. Utöver denna naturliga variation i klimatet, så har människan, under det senaste århundradet, medverkat till en ökning av växthusgaser i atmosfären. Detta kan innebära att växthuseffekten intensifieras och Jorden bli utsatt för onaturliga temperaturökningar. Koldioxid (CO2), från bland annat förbränning av fossila bränslen, är en av de mest diskuterade och viktigaste växthusgaserna. Förutom att CO2 skapas utifrån mänskliga aktiviteter, så har växthusgasen också ett nära samband med biosfären genom att den upptas genom växternas fotosyntes (produktion) och avges genom växternas respiration (andning). Ett liknande samband mellan klimat och biosfär finner man hos metan (CH4), som också är en viktig växthusgas och som avges i stora mängder från naturliga våtmarker, där den bildas av bakterier i syrefattiga miljöer. Fortsättningsvis så finns det ytterligare organiska sammansättningar (biogenic volatile organic compunds BVOCs), relativt lite studerade, som avges i gasform från vegetationen och där en av de största undergrupperna är icke-metan kolväten (non-methane hydrocarbons NMHCs). En del icke-metan kolväten har funnits vara en betydande del av kol-budgeten inom en del ekosystem, samtidigt som de har identifierats att påverka klimatet genom en rad komplisserade kemiska reaktioner i atmosfären. För att kunna modellera framtida klimatförändringar, på olika platser på jorden, så är det nödvändigt att inkludera den terrestra kolcykeln och alla dess komponenter, tillsammans med de mänskliga utsläppen av växthusgaser. Vi måste också förstå hur olika ekosystem kan komma att reagera på olika förändringar i klimatet och hur deras individuella kol-budget kan komma att förändras. Den här rapporten redogör för en studie av CO2, CH4, och icke-metan kolväten på Stordalen, en subarktisk myr i norra Sverige. Det finns mycket landområde på höga norra breddgrader som förutspås genomgå kraftiga temperaturstigningar i ett klimatförändrings-scenario, samtidigt som de kan komma att bli en stor kolkälla genom de stora mängder kol ansamlat i utbredda torvmaker. Syftet var att bidra till existerande kunskap om CO2 och CH4, men främst att tillföra ny kunskap om icke-metan kolväten i ett subarktiskt ekosystem. Fältarbete utfördes under sommarsäsongen 2003.

Flödet av de tre gaserna mättes från tre olika sub-ekosystem på Stordalen, namngivna genom deras fukt och näringsegenskaper: en semi-våt näringsfattig plats med mest Sphagnum mossor, en våt halvt näringsrik plats där det växer Eriophorum vagnitum (tuvull) samt en våt näringsrik plats med Eriophorum angustifolum (ängsull). Sex glaskammare var placerade på de olika platserna, och när en kammare stängdes så mätte ett datoriserat kontrollsystem koncentrationsförändringarna, vilka senare beräknades till ett positivt eller negative flöde. De olika flödena analyserades sedan säsongsmässigt och hur de var relaterade till varandra. Det genomfördes också regressionsanalyser med temperatur, ljus, vattennivå samt frysta lager i marken mm. Genom att göra dessa analyser så kan man försöka få svar på hur de olika kolföreningarna reagerar på olika variabler, hur stor del de har i ett ekosystems kolbudget och vilka effekterna kan komma att bli i ett klimatförändings-scenario.

Resultatet var att utsläpp av icke-metan kolväten, från de studerade sub-ekosystemen, generellt verkar bero på temperatur och solljus, och de fanns ha en viktig del i ekosystemets kolbudget. Under den studerade sommarsäsongen, så är det ett netto-upptag av CO2 från atmosfären till biosfären. Detta gäller för alla de olika sub-ekosystemen. Metanutsläppen är klart störst från de våta områdena. Konklusionen är att det finns ett behov av mer forskning inom icke-metankolväten från ekosystem på dessa nordliga latituder, tillsammans med kolföreningar som CO2 och CH4. Potentiellt så kan sådan här information i framtiden användas inom klimatmodellering för att förutspå klimatförändringar på olika platser på jorden, men vissa justeringar i metodiken i det här arbetet måste vidtas. (Less)
Please use this url to cite or link to this publication:
author
Bäckstrand, Kristina
supervisor
organization
alternative title
Dynamiska flöden av icke-metan kolväten och andra spårgaser från en subarktisk myr i norra Sverige
year
type
H1 - Master's Degree (One Year)
subject
keywords
geomorfologi, naturgeografi, climatology, cartography, climate change, carbon cycle, physical geography, nodelling, pedology, geomorphology, marklära, kartografi, klimatologi
publication/series
Lunds universitets Naturgeografiska institution - Seminarieuppsatser
report number
99
language
English
id
1332971
date added to LUP
2005-10-20
date last changed
2011-12-12 15:45:06
@misc{1332971,
  abstract     = {In the context of climate change, it is important to understand how the terrestrial carbon cycle is interacting with the anthropogenic increase in atmospheric carbon dioxide (CO2) concentration. Boreal and subarctic regions in the northern hemisphere are great carbon pools, as well as they are subject to predicted warming. These facts place them in the absolute frontline of ecosystems that are to be studied in the context of coupled climate models, where the terrestrial carbon cycle is included. In addition to CO2 and methane (CH4), which have been intensively studied regarding carbon cycle and climate, there are other biogenic volatile organic compounds (BVOC) emitted by vegetation that have shown to be of great importance. One group is called non-methane hydrocarbons (NMHCs). Their emissions is a part of the carbon flux in ecosystems, and have an indirect role in determining atmospheric concentration of some greenhouse gases as well as biogenic aerosols. A study of CO2, CH4 and NMHC flux dynamics has been conducted on the subarctic mire Stordalen in northern Sweden. The objective is to contribute to the existing knowledge about exchanges of CO2 and CH4, and primarily to add new knowledge of NMHC emissions from a subarctic ecosystem, which has not earlier been studied.
An automatic multichamber system was used to collect high temporal resolution data of CO2 and total hydrocarbon (THC) fluxes from three different sub-ecosystems on the mire: a wet minerotrophic site, a wet intermediate ombro-minerotrophic site and a semiwet ombrotrophic site. Further, manual sampling of CH4 fluxes was conducted approximately three times a week, from mid-June to late August. This gave the possibility to estimate the amount of NMHCs (THC flux -CH4 flux). A temperature dependent respiration model was developed from night time CO2 flux data, and gross primary production (GPP) could be estimated for each sub-ecosystem. Environmental variables as light, temperature, moisture and thaw depth are included in the correlations.
The results show a certain degree of temperature, light and GPP dependency for NMHC emissions from all of the different plant communities, however it is a great distinction between different plant specie. The largest emissions come from wet minerotrophic sub-ecosystems with vascular plants, compared to a mostly Sphagnum moss vegetated semiwet site, 2.8 mg/m2/hr and 0.9 mg/m2/hr respectively. The NMHC flux rates are however, likely to be underestimated. They are based on the molar weight of CH4 (16 g/mol), while isoprene (C5H8), which is one of the lightest NMHCs, have a molar weight that is more then four times greater. The output of NMHC-carbon from the mire ecosystem was found to be close to 2 % from the wet minerotrophic site, in relationship to CO2-C and CH4-C. CH4 emissions are higher from wet, compared to semiwet microsites. The water table position at a depth of 15-25 cm play an important role at the semiwet site, while water table variations within a depth of 0-10 cm do not affect the CH4 emissions. Moreover, the presence of vascular plants and their ability to give qualitative substrates for CH4 production through photosynthesis, as well as their capacity for plant mediated CH4 transport, are most likely explaining the difference between the two sites. This is in addition to the actual moisture content, explained as being the main cause for high CH4 emissions. Conclusively, research of BVOCs from northern latitude ecosystem like the subarctic mire Stordalen, should be a part in future studies of the terrestrial carbon cycle. Their part in the carbon budget at this site is shown to be significant.},
  author       = {Bäckstrand, Kristina},
  keyword      = {geomorfologi,naturgeografi,climatology,cartography,climate change,carbon cycle,physical geography,nodelling,pedology,geomorphology,marklära,kartografi,klimatologi},
  language     = {eng},
  note         = {Student Paper},
  series       = {Lunds universitets Naturgeografiska institution - Seminarieuppsatser},
  title        = {The dynamics of non-methane hydrocarbons and other trace gas fluxes at a subarctic mire in northern Sweden},
  year         = {2004},
}