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Forests and Greenhouse gases. Fluxes of CO2, CH4 and N2O from drained forests on organic soils
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

One of the largest environmental threats believed to be facing us today is global warming due to the accumulation of green house gases (GHG). The concentrations of GHG in the atmosphere are a result of the net strength of different sinks and sources. Forests, in this context, are of particular interest because of their dual role as both sinks and sources. Most forests are net sinks for CO2 but others, such as drained forests, may be significant sources of both CO2 and N20. Consequently, it is essential to understand the fluxes of GHG between drained forests and the atmosphere in order to obtain accurate estimates of national GHG budgets.

The findings reported in this thesis and the accompanying papers are based on dark chamber flux measurements of soil GHG fluxes and modelled annual net primary productions in five drained forest sites and two undrained sites situated on organic soil.

Temporal variations in forest floor CO2, release could be explained, to a large extent, by differencies in temperature and groundwater level. The within-site spatial variation in soil GHG fluxes could only be explained to a very small extent by distance to tree stems. Much of the among-site variations in soil CO2 and CH4 release could be caused by differences in the mean annual groundwater table, while N20 emissions were strongly correlated to the carbon-to-nitrogen ratio of soil organic matter. Most poorly drained forested areas are probably net sinks for GHG as the CO2 uptake by trees more than compensates for the soil GHG emissions. However, the total drained forested area in Sweden was estimated to be a net source of GHG. The CO2 release from decomposition of soil organic matter stored before drainage was estimated to be substantial. Corresponding to 15% of the CO2 release from the consumption of fossil fuels.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2004. , 47 p.
Series
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 302
Keyword [en]
Greenhouse gases, GHG, fluxes of CO2, CH4, drained forests, organic soils
Keyword [sv]
Skogsbotanik, miljöaspekter, växthusgaser
National Category
Oceanography, Hydrology, Water Resources
Identifiers
URN: urn:nbn:se:liu:diva-4853ISBN: 91-85295-71-X (print)OAI: oai:DiVA.org:liu-4853DiVA: diva2:20781
Public defence
2004-11-26, Elysion, Hus T, Campus Valla, Linköpings universitet, Linköping, 10:00 (English)
Supervisors
Note

On the day of the public defence of the doctoral thesis the status of the articles I and II was: Conditionally accepted; article III was: Submitted and articles IV and V was: Manuscript. The title of article III was on the day of the public defence "Can the distribution of trees explain the spatial variation in N2O emissions from boreal forest soils?".

Available from: 2004-12-12 Created: 2004-12-12 Last updated: 2014-09-02Bibliographically approved
List of papers
1. Fluxes of CO2, CH4 and N2O from drained coniferous forests on organic soils
Open this publication in new window or tab >>Fluxes of CO2, CH4 and N2O from drained coniferous forests on organic soils
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2005 (English)In: Forest Ecology and Management, ISSN 0378-1127, Vol. 210, no 1-3, 239-254 p.Article in journal (Refereed) Published
Abstract [en]

Fluxes of CO2, CH4 and N2O were measured during two to three years at four sites, located within an area of 9 km2 in southern Sweden, using dark static chamber techniques. Three of the sites were drained coniferous forests on moist organic soils that differed in forest productivity and tree species. The fourth site was an undrained tall sedge mire. Although the drained sites were all moist, with average groundwater levels between 17 and 27 cm below the soil surface, the mean annual dark forest floor CO2 release rate was significantly higher at the drained sites, (0.9–1.9 kg m−2 y−1) than at the undrained mire site (0.8 to 1.2 kg m−2 y−1). CH4 emissions were significantly lower from the drained sites than from the undrained mire (0.0 to 1.6 g m−2 y−1, compared to 10.6 to 12.2 g m−2 y−1), while N2O emissions were significantly lower from the undrained site than from the drained sites (20 to 30 mg m−2 y−1, compared to 30 to 90 mg m−2 y−1). There were no clear effects of site productivity or tree species on the soil fluxes of any of the gases. The annual net primary production of the forests was modeled. All drained sites were net sinks, while the undrained mire was a net source of greenhouse gases. The estimated net greenhouse gas exchange of the drained sites was correlated with productivity: the most productive site was the largest net sink and the least productive the smallest net sink for greenhouse gases. The results indicate that, to mitigate the increase of atmospheric greenhouse gases, drained forest sites, which have been unsuccessfully drained or rewetted due to subsidence, should be managed in a way that keeps the groundwater level at a steady state.

Keyword
Forestry drainage; Forest productivity; CO2 flux; CH4 flux; N2O flux
National Category
Oceanography, Hydrology, Water Resources
Identifiers
urn:nbn:se:liu:diva-13452 (URN)10.1016/j.foreco.2005.02.031 (DOI)
Available from: 2004-12-12 Created: 2004-12-12 Last updated: 2009-06-08
2. Fluxes of CO2, CH4 and N2O from drained organic soils in deciduous forests
Open this publication in new window or tab >>Fluxes of CO2, CH4 and N2O from drained organic soils in deciduous forests
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2005 (English)In: Soil Biology and Biochemistry, ISSN 0038-0717, Vol. 37, no 6, 1059-1071 p.Article in journal (Refereed) Published
Abstract [en]

We examined net greenhouse gas exchange at the soil surface in deciduous forests on soils with high organic contents. Fluxes of CO2, CH4 and N2O were measured using dark static chambers for two consecutive years in three different forest types; (i) a drained and medium productivity site dominated by birch, (ii) a drained and highly productive site dominated by alder and (iii) an undrained and highly productive site dominated by alder. Although the drained sites had shallow mean groundwater tables (15 and 18 cm, respectively) their average annual rates of forest floor CO2 release were almost twice as high compared to the undrained site (1.9±0.4 and 1.7±0.3, compared to 1.0±0.2 kg CO2 m−2 yr−1). The average annual CH4 emission was almost 10 times larger at the undrained site (7.6±3.1 compared to 0.9±0.5 g CH4 m−2 yr−1 for the two drained sites). The average annual N2O emissions at the undrained site (0.1±0.05 g N2O m−2 yr−1) were lower than at the drained sites, and the emissions were almost five times higher at the drained alder site than at the drained birch site (0.9±0.35 compared to 0.2±0.11 g N2O m−2 yr−1). The temporal variation in forest floor CO2 release could be explained to a large extent by differences in groundwater table and air temperature, but little of the variation in the CH4 and N2O fluxes could be explained by these variables. The measured soil variables were only significant to explain for the within-site spatial variation in CH4 and N2O fluxes at the undrained swamp, and dark forest floor CO2 release was not explained by these variables at any site. The between-site spatial variation was attributed to variations in drainage, groundwater level position, productivity and tree species for all three gases. The results indicate that N2O emissions are of greater importance for the net greenhouse gas exchange at deciduous drained forest sites than at coniferous drained forest sites.

Keyword
Forest drainage; Greenhouse effect; Methane; Carbon dioxide; Nitrous oxide; Organic soil; Tree species
National Category
Oceanography, Hydrology, Water Resources
Identifiers
urn:nbn:se:liu:diva-13453 (URN)10.1016/j.soilbio.2004.11.004 (DOI)
Available from: 2004-12-12 Created: 2004-12-12
3. Can distribution of trees explain variation in nitrous oxide fluxes?
Open this publication in new window or tab >>Can distribution of trees explain variation in nitrous oxide fluxes?
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2005 (English)In: Scandinavian Journal of Forest Research, ISSN 0282-7581, E-ISSN 1651-1891, Vol. 20, no 6, 481-489 p.Article in journal (Refereed) Published
Abstract [en]

The impact of distance to tree stems on nitrous oxide (N2O) fluxes was examined to determine whether it is possible to improve the accuracy of flux estimates from boreal forest soils. Dark static chambers were placed along transects between pairs of trees within a Norway spruce stand and fluxes of N2O and carbon dioxide (CO2) were measured during the period 1999-2003. The groundwater table was measured on every sampling occasion along the transects. In addition, radiation transmission, potential diffusion rate and biomass of forest floor vegetation were measured once at each chamber site along one of the transects and soil samples were collected at three depths, from which pH, denitrification enzyme activity, soil moisture, organic matter, and carbon and nitrogen content were determined. There was a high level of variation in the N2O fluxes, both spatially and temporally. However, the spatial variation in the N2O fluxes within the transect could not be explained by differences in any of the measured variables. Sometimes, mainly when no major peaks occurred, N2O fluxes were significantly correlated with CO2 release. It is concluded that distance to stems cannot be used to improve the design of sampling schemes or for extrapolating flux levels to larger scales.

Keyword
Denitrification, nitrogen transformation, nitrous oxide emission, root dynamics, spatial variation, spruce (Picea abies)
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13454 (URN)10.1080/02827580500443443 (DOI)
Available from: 2004-12-12 Created: 2004-12-12 Last updated: 2017-12-13Bibliographically approved
4. Soil CN ratio as a scalar parameter to predict nitrous oxide emissions
Open this publication in new window or tab >>Soil CN ratio as a scalar parameter to predict nitrous oxide emissions
2005 (English)In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 11, no 7, 1142-1147 p.Article in journal (Refereed) Published
Abstract [en]

Forested histosols have been found in some cases to be major, and in other cases minor, sources of the greenhouse gas nitrous oxide (N2O). In order to estimate the total national or global emissions of N2O from histosols, scaling or mapping parameters that can separate low- and high-emitting sites are needed, and should be included in soil databases. Based on interannual measurements of N2O emissions from drained forested histosols in Sweden, we found a strong negative relationship between N2O emissions and soil CN ratios (r2adj=0.96, mean annual N2O emission=ae(−b CN ratio)). The same equation could be used to estimate the N2O emissions from Finnish and German sites based on CN ratios in published data. We envisage that the correlation between N2O emissions and CN ratios could be used to scale N2O emissions from histosols determined at sampled sites to national levels. However, at low CN ratios (i.e. below 15–20) other parameters such as climate, pH and groundwater tables increase in importance as regulating factors affecting N2O emissions.

Keyword
CN ratio, drainage, histosol, mapping, nitrous oxide, scaling
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13455 (URN)10.1111/j.1365-2486.2005.00973.x (DOI)
Available from: 2004-12-12 Created: 2004-12-12 Last updated: 2017-12-13
5. Greenhouse gas fluxes from drained organic forestland in Sweden
Open this publication in new window or tab >>Greenhouse gas fluxes from drained organic forestland in Sweden
2005 (English)In: Scandinavian Journal of Forest Research, ISSN 0282-7581, Vol. 20, no 5, 400-411 p.Article in journal (Refereed) Published
Abstract [en]

The objective of this study was to estimate the contribution of drained organic forestlands in Sweden to the national greenhouse gas budget. Drained organic forestland in Sweden collectively comprises an estimated net sink for greenhouse gases of -5.0 Mt carbon dioxide (CO2) equivalents year-1 (range -12.0 to 1.2) when default emission factors provided by the Good practice guidance for land use, land-use change and forestry are used, and an estimated net source of 0.8 Mt CO2 equivalents year-1 (range -6.7 to 5.1) when available emission data for the climatic zones spanned by Sweden are used. This discrepancy is mainly due to differences in the emission factors for heterotrophic respiration. The main uncertainties in the estimates are related to carbon changes in the litter pool and releases of soil CO2 and nitrous oxide.

Keyword
Carbon dioxide; good practice guidance; greenhouse gas budget; methane; nitrous oxide; peat; scaling
National Category
Oceanography, Hydrology, Water Resources
Identifiers
urn:nbn:se:liu:diva-13456 (URN)10.1080/02827580500281975 (DOI)
Available from: 2004-12-12 Created: 2004-12-12

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Arnold, Karin von

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