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Methane exchange in a boreal forest: : the role of soils vegetation and forest management

Sundqvist, Elin LU (2014)
Abstract (Swedish)
Skogar har en positiv inverkan på halten av växthusgaser i atmosfären eftersom de binder koldioxid via fotsyntesen och lagrar kol i marken. Dessutom utgör många skogar en betydande sänka för växthusgasen metan. Upptaget av metan sker i väl syresatta marker genom oxidation utförd av metanotrofa bakterier. Däremot sker en nettoproduktion av metan i syrefattiga skogsmarker när mikroorganismer, s.k. arkéer bryter ner organiskt material. Metan löst i markvatten kan tas upp i träd och sedan avges genom stammar eller bladverk. Metan kan också bildas i gröna växter och emitteras, vilket främst sker när växter utsätts för hög UV-strålning, höga temperaturer eller skador på bladverken. Avhandlingen fokuserar på metanutbytet i ett borealt skogsområde... (More)
Skogar har en positiv inverkan på halten av växthusgaser i atmosfären eftersom de binder koldioxid via fotsyntesen och lagrar kol i marken. Dessutom utgör många skogar en betydande sänka för växthusgasen metan. Upptaget av metan sker i väl syresatta marker genom oxidation utförd av metanotrofa bakterier. Däremot sker en nettoproduktion av metan i syrefattiga skogsmarker när mikroorganismer, s.k. arkéer bryter ner organiskt material. Metan löst i markvatten kan tas upp i träd och sedan avges genom stammar eller bladverk. Metan kan också bildas i gröna växter och emitteras, vilket främst sker när växter utsätts för hög UV-strålning, höga temperaturer eller skador på bladverken. Avhandlingen fokuserar på metanutbytet i ett borealt skogsområde vid forskningsstationen Norunda i mellansverige. Syftet är att genom fältmätningar kvantifiera nettoutbytet av metan i skogen och undersöka vilka faktorer som utgör den huvudsakliga kontrollen av utbytet i mark och vegetation. Effekter av slutavverkning, stubbskörd och gallring på metanutbytet studeras också.

Kyvettmätningar på ytor i ostörd och gallrad skog visar att marken i Norunda är en sänka av metan. Metanupptaget gynnas generellt av ett stort avstånd från markytan till grundvattnet, en låg markfukt, och höga marktemperaturer. Kyvettmätningar på en slutavverkad och en stubbskördad yta visar däremot på nettoemissioner av metan från marken, vilket hänger samman med en höjd grundvattennivå och ökad markfukt till följd av avverkningen. Grenkyvettmätningar på skott av gran, tall, björk och rönn visar också på ett upptag av metan vilket står i kontrast till tidigare studier, mestadels utförda i laboratorier, som funnit nettoemissioner från växter. Upptaget i vegetationen korrelerar med det fotosyntetiskt aktiva ljuset vilket tyder på en koppling till fotosyntesen. Till skillnad från våra mätningar på mark och vegetation så visar resultat från våra mikrometerorologiska mätningar ovanför trädkronorna på nettoemissioner från skogen till atmosfären. Då dessa mätningar representerar ett större område än de ytor som kyvettmätningarna är gjorda på skulle skillnaden kunna förklaras med att metanproduktionen i små blöta områden är så hög att den dominerar upptaget i den övriga marken. En uppskalning av markmätningarna baserat på höjddata indikerar dock att marken i det centrala studieområdet är en sänka av metan trots en del mindre partier med produktion. Emissioner från vegetationen eller transport av metan från omkringliggande källområden är andra tänkbara förklaringar till skillnader mellan mätningarna. (Less)
Abstract
Popular Abstract in English

Forests have a positive impact on the level of greenhouse gases in the atmosphere because they absorb carbon dioxide through photosynthesis and store carbon in the soil. Moreover, many forests function as a sink for the greenhouse gas methane (CH4). The uptake of CH4 takes place in well-aerated soils through oxidation by methanotrophic bacteria. However, there is a net production of CH4 in anaerobic soils, such as submerged soils, by microorganisms, archaeans. CH4 dissolved in ground water can be taken up by trees and discharged through stems or foliage. CH4 can also be formed in green plants and emitted, which mainly occurs when plants are exposed to high UV radiation, high temperature, or if... (More)
Popular Abstract in English

Forests have a positive impact on the level of greenhouse gases in the atmosphere because they absorb carbon dioxide through photosynthesis and store carbon in the soil. Moreover, many forests function as a sink for the greenhouse gas methane (CH4). The uptake of CH4 takes place in well-aerated soils through oxidation by methanotrophic bacteria. However, there is a net production of CH4 in anaerobic soils, such as submerged soils, by microorganisms, archaeans. CH4 dissolved in ground water can be taken up by trees and discharged through stems or foliage. CH4 can also be formed in green plants and emitted, which mainly occurs when plants are exposed to high UV radiation, high temperature, or if the foliage is damaged. The work in this thesis focus on the CH4 exchange in a boreal forest, at the research station Norunda, in central Sweden. The aim is to quantify the net CH4 exchange at the site and investigate what factors constitute the main control of the exchange in soil and vegetation. The impact of clear-cutting, stump harvesting and thinning on the CH4 exchange was also studied.

Chamber measurements in undisturbed and thinned forest show that the soil is a sink of CH4. The uptake generally benefits from a large groundwater depth, low soil moisture and high temperatures. Chamber measurements on clear-cut and stump harvested plots show net emissions, which is associated with increased groundwater levels and increased soil moisture as a result of harvesting. Branch chamber measurements on shoots of spruce, pine, birch and rowan also show an uptake of CH4, which is in contrast to previous studies, mostly done in laboratories, which found net emissions from plants. Uptake by vegetation correlated with photosynthetically active radiation, which indicates a coupling to photosynthesis. Unlike our measurements on soil and vegetation, results from our micrometeorological measurements above the canopy showed net emissions from the forests to the atmosphere. These measurements represented a larger area than the chambers and differences could therefore be explained by large CH4 production in small wet areas, which exceeds the uptake in the rest of the soil. However, scaling of soil chamber measurements based on elevation data, indicate that the soil in the main study area was a sink of CH4 regardless of some minor areas with CH4 production. CH4 emissions from vegetation or transport of CH4 from surrounding source areas are other possible explanations for this discrepancy. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • professor Ambus, Per, Technical University of Denmark
organization
publishing date
type
Thesis
publication status
published
subject
keywords
chamber measurements, gradient measurements, clear-cut, topography, water table depth
publisher
Department of Physical Geography and Ecosystem Science, Lund University
defense location
lecture hall Pangea, Sölvegatan 12
defense date
2014-06-12 10:00
ISBN
978-91-85793-39-6
language
English
LU publication?
yes
id
e7dd3418-4c5e-4dc6-8682-dc697887011d (old id 4438134)
date added to LUP
2014-09-04 12:43:32
date last changed
2016-09-19 08:45:14
@misc{e7dd3418-4c5e-4dc6-8682-dc697887011d,
  abstract     = {<b>Popular Abstract in English</b><br/><br>
Forests have a positive impact on the level of greenhouse gases in the atmosphere because they absorb carbon dioxide through photosynthesis and store carbon in the soil. Moreover, many forests function as a sink for the greenhouse gas methane (CH4). The uptake of CH4 takes place in well-aerated soils through oxidation by methanotrophic bacteria. However, there is a net production of CH4 in anaerobic soils, such as submerged soils, by microorganisms, archaeans. CH4 dissolved in ground water can be taken up by trees and discharged through stems or foliage. CH4 can also be formed in green plants and emitted, which mainly occurs when plants are exposed to high UV radiation, high temperature, or if the foliage is damaged. The work in this thesis focus on the CH4 exchange in a boreal forest, at the research station Norunda, in central Sweden. The aim is to quantify the net CH4 exchange at the site and investigate what factors constitute the main control of the exchange in soil and vegetation. The impact of clear-cutting, stump harvesting and thinning on the CH4 exchange was also studied.<br/><br>
Chamber measurements in undisturbed and thinned forest show that the soil is a sink of CH4. The uptake generally benefits from a large groundwater depth, low soil moisture and high temperatures. Chamber measurements on clear-cut and stump harvested plots show net emissions, which is associated with increased groundwater levels and increased soil moisture as a result of harvesting. Branch chamber measurements on shoots of spruce, pine, birch and rowan also show an uptake of CH4, which is in contrast to previous studies, mostly done in laboratories, which found net emissions from plants. Uptake by vegetation correlated with photosynthetically active radiation, which indicates a coupling to photosynthesis. Unlike our measurements on soil and vegetation, results from our micrometeorological measurements above the canopy showed net emissions from the forests to the atmosphere. These measurements represented a larger area than the chambers and differences could therefore be explained by large CH4 production in small wet areas, which exceeds the uptake in the rest of the soil. However, scaling of soil chamber measurements based on elevation data, indicate that the soil in the main study area was a sink of CH4 regardless of some minor areas with CH4 production. CH4 emissions from vegetation or transport of CH4 from surrounding source areas are other possible explanations for this discrepancy.},
  author       = {Sundqvist, Elin},
  isbn         = {978-91-85793-39-6},
  keyword      = {chamber measurements,gradient measurements,clear-cut,topography,water table depth},
  language     = {eng},
  publisher    = {ARRAY(0xa304ed8)},
  title        = {Methane exchange in a boreal forest: : the role of soils vegetation and forest management},
  year         = {2014},
}