| 1. |
- He, Hongxing, 1987, et al.
(author)
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Factors controlling Nitrous Oxide emission from a spruce forest ecosystem on drained organic soil, derived using the CoupModel
- 2016
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In: Ecological Modelling. - : Elsevier. - 0304-3800 .- 1872-7026. ; 321, s. 46-63
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Journal article (peer-reviewed)abstract
- High Nitrous Oxide (N2O) emissions have been identified in hemiboreal forests in association with draining organic soils. However, the specific controlling factors that regulate the emissions remain unclear. To examine the importance of different factors affecting N2O emissions in a spruce forest on drained organic soil, a process-based model, CoupModel, was calibrated using the generalized likelihood uncertainty estimation (GLUE) method. The calibration also aims to estimate parameter density distributions, the covariance matrix of estimated parameters and the correlation between parameters and variables information, useful when applying the model on other peat soil sites and for further model improvements. The calibrated model reproduced most of the high resolution data (total net radiation, soil temperature, groundwater level, net ecosystem exchange, etc.) very well, as well as cumulative measured N2O emissions (simulated 8.7±1.1kgN2Oha-1year-1 (n=97); measured 8.7±2.7kgN2Oha-1year-1 (n=6)), but did not capture every measured peak. Parameter uncertainties were reduced after calibration, in which 16 out of 20 parameters changed from uniform distributions into normal distributions or log normal distributions. Four parameters describing bypass water flow, oxygen diffusion and soil freezing changed significantly after calibration. Inter-connections and correlations between many calibrated parameters and variables reflect the complex and interrelated nature of pedosphere, biosphere and atmosphere interactions. This also highlights the need to calibrate a number of parameters simultaneously. Model sensitivity analysis indicated that N2O emissions during growing seasons are controlled by competition between plants and microbes for nitrogen, while during the winter season snow melt periods are important. Our results also indicate that N2O is mainly produced in the capillary fringe close to the groundwater table by denitrification in the anaerobic zone. We conclude that, in afforested drained peatlands, the plants and groundwater level have important influences on soil N availability, ultimately controlling N2O emissions.
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| 2. |
- He, Hongxing, 1987, et al.
(author)
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Forests on drained agricultural peatland are potentially large sources of greenhouse gases – insights from a full rotation period simulation
- 2015
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In: Biogeosciences Discussions. - : Copernicus GmbH. - 1810-6277. ; 12, s. 19673-19710
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Journal article (peer-reviewed)abstract
- The CoupModel was used to simulate a Norway Spruce forest on fertile drained peat over 60 years, from planting in 1951 until 2011, describing abiotic, biotic and greenhouse gas (GHG) emissions (CO2 and N2O). By calibrating the model against tree ring data we obtained a "reference" model by which we were able to describe the fluxes and controlling factors over the 60 years. We discuss some conceptual issues relevant to improving the model in order to better understand peat soil simulations. However, the present model was able to describe the most important ecosystem dynamics such as the plant biomass development and GHG emissions. The GHG fluxes are composed of two important quantities, the forest carbon (C) uptake, 405 g C m−2 yr−1 and the decomposition of peat soil, 396 g C m−2 yr−1. N2O emissions contribute to the GHG emissions by 0.5 g N m−2 yr−1, corresponding to 56.8 g C m−2 yr−1. The 60-year-old Spruce forest has an accumulated biomass of 164 Mg C ha−1. However, over this period 208 Mg C ha−1 GHG has been added to the atmosphere, which means a net addition of GHG emissions. The main losses are from the peat soil and, indirectly, from forest thinning products, which we assume have a short lifetime. We conclude that after harvest at an age of 80 years, most of the stored biomass carbon is liable to be released, the system having captured C only temporarily and with a cost of disappeared peat, adding CO2 to the atmosphere.
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| 3. |
- He, Hongxing, 1987, et al.
(author)
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Forests on drained agricultural peatland are potentially large sources of greenhouse gases – insights from a full rotation period simulation
- 2016
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In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 13
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Journal article (peer-reviewed)abstract
- The CoupModel was used to simulate a Norway spruce forest on fertile drained peat over 60 years, from planting in 1951 until 2011, describing abiotic, biotic and greenhouse gas (GHG) emissions (CO2 and N2O). By calibrating the model against tree ring data a “vegetation fitted” model was obtained by which we were able to describe the fluxes and controlling factors over the 60 years. We discuss some conceptual issues relevant to improving the model in order to better understand peat soil simulations. However, the present model was able to describe the most important ecosystem dynamics such as the plant biomass development and GHG emissions. The GHG fluxes are composed of two important quantities, the spruce forest carbon (C) uptake, 413 g C m-2 yr-1 and the decomposition of peat soil, 399 gCm-2 yr-1. N2O emissions contribute to the GHG emissions by up to 0.7 gNm-2 yr-1, corresponding to 76 g Cm-2 yr-1. The 60-year old spruce forest has an accumulated biomass of 16.0 kg Cm-2 (corresponding to 60 kgCO2 m-2). However, over this period, 26.4 kg m-2 (97 kgCO2eqm-2) has been added to the atmosphere, as both CO2 and N2O originating from the peat soil and, indirectly, from forest thinning products, which we assume have a short lifetime. We conclude that after harvest at an age of 80 years, most of the stored biomass carbon is liable to be released, the system having captured C only temporarily and with a cost of disappeared peat, adding CO2 to the atmosphere.
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| 4. |
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| 5. |
- He, Hongxing, 1987, et al.
(author)
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Modeling Nitrous Oxide emissions and identifying emission controlling factors for a spruce forest ecosystem on drained organic soil
- 2015
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In: Geophysical Research Abstracts. ; 17:EGU2015-10451
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Conference paper (other academic/artistic)abstract
- High Nitrous Oxide (N2O) emission has been identified in hemiboreal forests on drained organic soils. However, the controlling factors regulating the emissions have been unclear. To examine the importance of different factors on the N2O emission in a spruce forest on drained organic soil, a process-based model, CoupModel, was calibrated by the generalized likelihood uncertainty estimation (GLUE) method. The calibrated model reproduced most of the high resolution data (total net radiation, soil temperature, groundwater level, net ecosystem exchange, etc.) very well, as well as accumulated measured N2O emissions, but showed difficulties to capture all the measured emission peaks. Parameter uncertainties could be reduced by combining selected criteria with the measurement data. The model showed the N2O emissions during the summer to be controlled mainly by the competition between plants and microbes while during the winter season snow melt periods are important. The simulated N budget shows >100 kg N ha-1 yr-1 to be in circulation between soil and plants and back again. Each year the peat mineralization adds about 60 kg N ha-1 and atmospheric deposition 12 kg N ha-1. Most of the mineralized litter and peat N is directly taken up by the plants but only a part accumulates in the plant biomass. As long as no timber is harvested the main N loss from the system is through nitrate leaching (30 kg N ha-1 yr-1) and gas emissions (20 kg N ha-1 yr-1), 55% as NO, 27% as N2O and 18% as N2. Regarding N2O gas emissions, our modeling indicates denitrification to be the most responsible process, of the size 6 kg N ha-1 yr-1, which could be compared to 0.04 kg N ha-1 yr-1 from nitrification. Our modelling also reveal 88% of the N2O mainly to be produced by denitrification in the capillary fringe (c.a. 40-60 cm below soil surface) of the anaerobic zone using nitrate produced in the upper more aerobic layers. We conclude N2O production/emission to be controlled mainly by the complex interaction between soil N availability, mediated by mineralization, nitrification, and plant growth together with soil anaerobicity controlled by the groundwater level. The model is currently used for modelling greenhouse gas emissions from drained organic soils over the entire forest cycle, from plantation to harvest. Different land use and plant production are compared like Spruce, Willow and Reed Canary Grass as well as rewetting options.
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| 6. |
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| 7. |
- Kasimir, Åsa, 1956, et al.
(author)
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Lower greenhouse gas flux and better economy with wetter peat soil use
- 2019
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In: Geophysical Research AbstractsVol. 21, EGU2019-14821, 2019.
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Conference paper (other academic/artistic)abstract
- We have used the CoupModel to investigate effects of 80 years of peatland use on greenhouse gas (GHG) emissions for four scenarios (1) business as usual - Norway spruce with average soil water table depth (WTD) of -40 cm; (2) willow plantation with WTD at -20 cm; (3) reed canary grass production with WTD at -10 cm; and (4) a fully rewetted peatland with no harvested product. Total soil GHG emissions for the scenarios were (including litter and peat respiration CO2 emissions as well as N2O and CH4) on average 33, 19, 15, and 11 Mg CO2eq ha-1year-1. No peat was lost for the wet peatland. At WTD -10 cm GHG emissions were at a minimum. Economy was analyzed by a cost–benefit analysis (CBA) where scenario (1) with spruce included gain from sold products like timber, pulpwood and energy biomass, and scenarios (2) and (3) harvests were for bioenergy purpose. Stored C in biomass and litter was included as gains, as well as biodiversity gains for the rewetted scenario. Costs included management and soil emissions. The CBA showed on average the best result for the rewetted peatland (4) and next were willow (2) together with reed canary grass (3), while spruce (1) production economic benefit was the lowest. This showed wetter condition to be a gain for the climate as well as for the economy. Questions to resolve are influences of fluctuating water tables and vegetation types on CH4 and N2O emission as well as DOC/DON loss etc. Continuation Clear-cut of forest followed by either continued forest or wetland restoration. We are now to clear-cut the mature spruce forest at Skogaryd research station, on which the model was calibrated. Half the area will then still be drained and planted with spruce and the other half rewetted to a wet meadow by building a dam. Collection of ecosystem and flux data will continue. We will now use the model to investigate the two scenarios, where we are most interested in effects on GHG and water DOC/DON losses, results presented here.We will also gain further knowledge on GHG and other losses from agricultural peat soils in the project Climate Smart Use of Norwegian organic soils (MYR). We will calibrate the CoupModel on data generated from the project and use it for investigating alternative land use options (wetter soil and lower management intensity at cultivated peatlands). In this later step, we want co-operate with research groups using other models.
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| 8. |
- Kasimir, Åsa, 1956, et al.
(author)
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Mosses are Important for Soil Carbon Sequestration in Forested Peatlands
- 2021
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In: Frontiers in Environmental Science. - : Frontiers Media SA. - 2296-665X. ; 9
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Journal article (peer-reviewed)abstract
- Nutrient-rich peat soils have previously been demonstrated to lose carbon despite higher photosynthesis and litter production compared to nutrient-poor soils, where instead carbon accumulates. To understand this phenomenon, we used a process-oriented model (CoupModel) calibrated on data from two closely located drained peat soil sites in boreal forests in Finland, Kalevansuo and Lettosuo, with different soil C/N ratios. Uncertainty-based calibrations were made using eddy-covariance data (hourly values of net ecosystem exchange) and tree growth data. The model design used two forest scenarios on drained peat soil, one nutrient-poor with dense moss cover and another with lower soil C/N ratio with sparse moss cover. Three vegetation layers were assumed: conifer trees, other vascular plants, and a bottom layer with mosses. Adding a moss layer was a new approach, because moss has a modified physiology compared to vascular plants. The soil was described by three separate soil organic carbon (SOC) pools consisting of vascular plants and moss litter origin and decomposed organic matter. Over 10 years, the model demonstrated a similar photosynthesis rate for the two scenarios, 903 and 1,034 g C m(-2) yr(-1), for the poor and rich site respectively, despite the different vegetation distribution. For the nutrient-rich scenario more of the photosynthesis produce accumulated as plant biomass due to more trees, while the poor site had abundant moss biomass which did not increase living aboveground biomass to the same degree. Instead, the poor site showed higher litter inputs, which compared with litter from vascular plants had low turnover rates. The model calibration showed that decomposition rate coefficients for the three SOC pools were similar for the two scenarios, but the high quantity of moss litter input with low decomposability for the nutrient poor scenario explained the major difference in the soil carbon balance. Vascular plant litter declined with time, while SOC pools originating from mosses accumulated with time. Large differences between the scenarios were obtained during dry spells where soil heterotrophic respiration doubled for the nutrient-rich scenario, where vascular plants dominated, owing to a larger water depletion by roots. Where moss vegetation dominated, the heterotrophic respiration increased by only 50% during this dry period. We suggest moss vegetation is key for carbon accumulation in the poor soil, adding large litter quantities with a resistant quality and less water depletion than vascular plants during dry conditions.
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| 9. |
- Kasimir, Åsa, 1956, et al.
(author)
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Spruce forest on drained peat – clear-cut winter 2019, half replanted and half rewetted into meadow
- 2019
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In: Abstract Book. pp 128.
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Conference paper (other academic/artistic)abstract
- We have used the CoupModel to investigate effects on GHG emissions as well as on economy of 80 years of peatland use for four scenarios (1) business as usual – Norway spruce with average soil water table depth (WTD) of -40 cm; (2) willow plantation with WTD at -20 cm; (3) reed canary grass production with WTD at -10 cm; and (4) a fully rewetted peatland with no harvested product. Total soil GHG emissions for the scenarios were (including litter and peat respiration CO2 emissions as well as N2O and CH4) on average 33, 19, 15, and 11 Mg CO2eq ha-1 yr-1. No peat was lost for the wet peatland. GHG emissions were at a minimum at WTD -10 cm. Economy was analyzed by a cost – benefit analysis (CBA) where scenario (1) with spruce included gain from sold products like timber, pulpwood and energy biomass, and scenarios (2) and (3) gains from energy biomass. Gains over the 80 years resulted also from stored C in biomass and litter as well as biodiversity for scenario (4). Costs included management and soil emissions. The CBA showed on average the best result for the rewetted peatland (4) while spruce (1) production’s economic benefit was the lowest. We are now about to clear-cut the mature spruce forest at Skogaryd research station, on which the model was calibrated. Half the area will then still be drained and planted with spruce and the other half rewetted to a wet meadow by building a dam. Collection of ecosystem and flux data has been extensive for more than a decennia and will continue. Researchers are invited for investigations following the changes taking place after the clear cut. We will present projected losses to air and water estimated by the CoupModel.
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