| 1. |
- Petrescu, A. M. R., et al.
(author)
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Modelling CH4 emissions from arctic wetlands : effects of hydrological parameterization
- 2008
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In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 5:1, s. 111-121
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Journal article (peer-reviewed)abstract
- This study compares the CH4 fluxes from two arctic wetland sites of different annual temperatures during 2004 to 2006. The PEATLAND-VU model was used to simulate the emissions. The CH4 module of PEATLAND-VU is based on the Walter-Heimann model. The first site is located in northeast Siberia, Indigirka lowlands, Kytalyk reserve (70 degrees N, 147 degrees E) in a continuous permafrost region with mean annual temperatures of -14.3 degrees C. The other site is Stordalen mire in the eastern part of Lake Tornetrask (68 degrees N, 19 degrees E) ten kilometres east of Abisko, northern Sweden. It is located in a discontinuous permafrost region. Stordalen has a sub arctic climate with a mean annual temperature of -0.7 degrees C. Model input consisted of observed temperature, precipitation and snow cover data. In all cases, modelled CH4 emissions show a direct correlation between variations in water table and soil temperature variations. The differences in CH4 emissions between the two sites are caused by different climate, hydrology, soil physical properties, vegetation type and NPP. For Kytalyk the simulated CH4 fluxes show similar trends during the growing season, having average values for 2004 to 2006 between 1.29-2.09 mg CH4 m(-2) hr(-1). At Stordalen the simulated fluxes show a slightly lower average value for the same years (3.52 mg CH4 m(-2) hr(-1)) than the observed 4.7 mg CH4 m(-2) hr(-1). The effect of the longer growing season at Stordalen is simulated correctly. Our study shows that modelling of arctic CH4 fluxes is improved by adding a relatively simple hydrological model that simulates the water table position from generic weather data. Our results support the generalization in literature that CH4 fluxes in northern wetland are regulated more tightly by water table than temperature. Furthermore, parameter uncertainty at site level in wetland CH4 process models is an important factor in large scale modelling of CH4 fluxes.
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| 2. |
- Yurova, Alla, et al.
(author)
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Carbon storage in the organic layers of boreal forest soils under various moisture conditions: A model study for Northern Sweden sites
- 2007
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In: Ecological Modelling. - : Elsevier BV. - 0304-3800. ; 204:3-4, s. 475-484
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Journal article (peer-reviewed)abstract
- A typical feature of the boreal forest landscape is a gradient from dry to wet sites, with associated increases in the depth of the soil organic layers. In this study, the coupled ecosystem-soil biogeochemistry model GUESS-ROMUL is used to explore how the specific features of soil organic matter decomposition and vegetation dynamics account for an observed difference between the soils formed under contrasting moisture conditions. Two sites, one mesic and one mesic-to-wet, representative of the natural forest in Northern Sweden, are simulated. In addition to the assumptions underlying the GUESS-ROMUL model, it is assumed that the fire frequency was higher at the mesic site. The model shows that with a natural fire regime, the soil organic layers at the mesic-to-wet site store 6.0 kg C m(-2) compared to 3.1 kg C m(-2) at the mesic site. Forty-seven percent of the difference between the sites in this respect is explained by suppressed decomposition under higher moisture conditions, 37% by the decreased litter input into the soil (more frequently disturbed ecosystems have lower productivity) and 16% by direct consumption of the forest floor in fires. It is predicted that due to anthropogenic fire suppression the organic soil layers of mesic sites will, in the future, sequester carbon at an average rate of 0.0103 kg C m(-2) year(-1) and have an equilibrium storage capacity of 5.4 kg C m(-2). For the mesic-to-wet site, the model predicts an extremely slow sequestration rate of 0.0022 kg C m(-2) year(-1). The effect of increased precipitation on the carbon storage at the landscape level is also investigated.
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| 3. |
- Yurova, Alla
(author)
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Hydrological aspects of the carbon balance in a boreal catchment: A model study
- 2007
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Doctoral thesis (other academic/artistic)abstract
- AbstractThe cycling of carbon in its gaseous, solid and dissolved forms is of central importance to ecosystem science, particularly, when the natural carbon cycle has been perturbed by human activity. Mathematical models are commonly used to asses and predict global and regional patterns of terrestrial carbon exchange. At the same time, processes operating on smaller (sub-grid) scales are usually outside the scope of the large-scale models exploring climate?biosphere interactions. However, if a sub-grid feature is found repeatedly in a large number of particular realizations, we may expect that its characteristic dynamics are likely to be important even at larger scales. This work examines some of these phenomena. First, a boreal landscape differentiated into forests and peatlands is investigated. Second, the export of dissolved organic carbon (DOC) in peatland streams is assessed.The work described herein mainly addresses methodology, i.e. how approaches to hydrology and ecosystem modelling can be combined. Specifically, the general ecosystem model GUESS was modified and supplied with new modules to be used for peatland simulations. The model was also designed to reproduce soil moisture and related ecosystem properties along a topographical catena. In addition, a completely new model of DOC production, transport and transformation in peat was developed. The data for model development and validation came from boreal catchments in the Vindelns Forest Research Parks, The Swedish University of Agricultural Sciences, Northern Sweden. A relatively good fit between the modelled and measured NEE at the Degerö Stormyr peatland was demonstrated for 2001-2003. Further, the model was used to demonstrate that the NEE was quite insensitive to changes in water table level within the ranges typical for the dominant mire plant community. The newly constructed model was able to reproduce DOC concentrations measured at the outlet of the Kallkälsmyren peatland for 1993-2001. The model suggested that the main drivers for interannual variability in DOC concentrations were the rates of microbially mediated DOC production and mineralization and the flow intensity in the active surface layer of the peatland. The amount of DOC in the peat water at a particular time was mainly determined by (much larger) amounts of soluble carbon sorbed on the peat matrix. A dynamic, rather than static, description of the adsorption and desorption processes was advocated.The work makes some contribution to filling the gap that currently exists between field observations at the plot scale and large-scale model analysis of the climate?biosphere interaction.
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| 4. |
- Yurova, Alla, et al.
(author)
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Modeling the dissolved organic carbon output from a boreal mire using the convection-dispersion equation: Importance of representing sorption
- 2008
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In: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 44:7
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Journal article (peer-reviewed)abstract
- In this paper we present a model of the dissolved organic carbon (DOC) concentrations and fluxes in mire water based on the convection-dispersion equation. The dynamics of sorbed, potentially soluble organic carbon (SPSOC) in the peat matrix are simulated in parallel with DOC. First, the model is applied solely to stagnant water conditions in order to interpret the results of laboratory peat incubations, with the focus on sorption processes. Some important model parameters are derived using literature data complemented by information from new incubation experiments. Second, the model is fully applied to simulate the DOC concentrations in the outlet of a steam draining a small headwater mire in northern Sweden during the period 1993-2001. A relatively good model fit (mean bias error (MBE) = -0.6-2.2 mg L-1, Willmott index of agreement d > 0.7 for the daily concentrations) was found for all the categories of stream discharge, except periods with very low flow (q < 0.3 mm d(-1)). When seeking explanations for the interannual variability in DOC concentrations, we, like previous authors, could find the influence of temperature, flow path, and intensity. However, the model has helped to demonstrate that the system also has a "memory'': the store of sorbed, potentially soluble organic carbon in a year affects the DOC concentrations and fluxes in the following year.
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| 5. |
- Yurova, Alla, et al.
(author)
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Variations in net ecosystem exchange of carbon dioxide in a boreal mire: Modeling mechanisms linked to water table position
- 2007
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In: Journal of Geophysical Research. - : John Wiley & Sons. - 2156-2202 .- 0148-0227. ; 112:G2
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Journal article (peer-reviewed)abstract
- [1] In mires, which occupy large areas of the boreal region, net ecosystem CO2 exchange ( NEE) rates vary significantly over various timescales. In order to examine the effect of one of the most influencing variables, the water table depth, on NEE the general ecosystem model GUESS-ROMUL was modified to predict mire daily CO2 exchange rates. A simulation was conducted for a lawn, the most common microtopographical feature of boreal oligotrophic minerotrophic mires. The results were validated against eddy covariance CO2 flux measurements from Degero Stormyr, northern Sweden, obtained during the period 2001 - 2003. Both measurements and model simulations revealed that CO2 uptake was clearly controlled by interactions between water table depth and temperature. Maximum uptake occurred when the water table level was between 10 and 20 cm and the air temperature was above 15 degrees C. When the water table was higher, the CO2 uptake rate was lower, owing to reduced rates of photosynthetic carbon fixation. When the water table was lower, NEE decreased owing to the increased rate of decomposition of organic matter. When the water table level was between 10 and 20 cm, the NEE was quite stable and relatively insensitive to both changes within this range and any air temperature changes above + 15 degrees C. The optimal water table level range for NEE corresponds to that characteristic of mire lawn plant communities, indicating that the annual NEE will not change dramatically if climatic conditions remain within the optimal range for the current plant community.
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