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- He, Hongxing, 1987, et al.
(författare)
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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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Ingår i: Ecological Modelling. - : Elsevier. - 0304-3800 .- 1872-7026. ; 321, s. 46-63
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 13, s. 2305-2318
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Tidskriftsartikel (refereegranskat)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. |
- He, Hongxing, 1987
(författare)
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Land use GHG emissions and mitigation options, simulated by CoupModel
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Climate change and greenhouse gas (GHG) emissions are one of the major challenges to the humankind of 21st Century. This thesis focuses on understanding, estimating and suggesting mitigation of the GHG emissions (mainly N2O and CO2) from the land use sector, specifically from forest ecosystems on drained peatlands but also from willow production on agricultural clay soil. This is achieved by merging a detailed process-oriented model, CoupModel with available data collected with state of art measurement techniques. The results show the CoupModel is able to simulate soil N2O and CO2 emissions for both land use types, despite not precisely capturing each measured N2O peak, which still remains a challenge. Model analysis reveals the major N2O emission controlling factors for afforested drained peatlands are vegetation and groundwater level, while fertilization and soil water status are the controlling factors for willow production on clay soil. Over a full forest rotation the forest trees act as a C sink and the drained peat soil as a source, of fairly similar size and the forest ecosystem is an overall GHG sink. However, also including the fate of the harvested forest, indirect GHG emissions, would switch this extended system (from the production site to the fate of the products) into an overall large GHG source. The modelling also predicts rewetting spruce forest on drained peatlands into willow, reed canary grass or wetland could possibly avoid GHG emissions by 33%, 72% and 89% respectively. In a cost-benefit analysis, the two wettest scenarios, wetland and reed canary grass, the monetized social benefits exceed the costs, when using social costs of carbon as a proxy for the value of GHG emissions, beside profits made from sold products and also value of biodiversity, avoided CO2 due to both replacement of cement and steel in buildings as well as fossil fuels for heating and electricity production. These findings provided in this thesis fill some knowledge gaps of modeling N2O emission and GHG balance over full forest rotation on drained peatlands, provide perspectives for mitigation GHG emissions from drained peatlands and bioenergy production on clay soil. In addition, the calibrated parameters and correlations between the parameter and variables in this thesis provide guidelines for future modeling of GHG for similar types of systems.
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