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Carbon budget estimation of a subarctic catchment using a dynamic ecosystem model at high spatial resolution

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  • Large amount of organic carbon is stored in high latitude soils. A substantial proportion of this carbon stock is vulnerable and may decompose rapidly due to temperature increases that are already greater than the global average. It is therefore crucial to quantify and understand carbon exchange between the atmosphere and subarctic/arctic ecosystems. In this paper, we combine an arctic-enabled version of the process-based dynamic ecosystem model, LPJ-GUESS (version LPJG-WHyMe-TFM) with comprehensive observations of terrestrial and aquatic carbon fluxes to simulate long-term carbon exchange in a subarctic catchment comprising both mineral and peatland soils. The model is applied at 50 m resolution and is shown to be able to capture the seasonality and magnitudes of observed fluxes at this fine scale. The modelled magnitudes of CO₂ uptake generally follow the descending sequence: birch forest, non-permafrost Eriophorum, Sphagnum and then tundra heath during the observation periods. The catchment-level carbon fluxes from aquatic systems are dominated by CO₂ emissions from streams. Integrated across the whole catchment, we estimate that the area is a carbon sink at present, and will become an even stronger carbon sink by 2080, which is mainly a result of a projected densification of birch forest and its encroachment into tundra heath. However, the magnitudes of the modelled sinks are very dependent on future atmospheric CO₂ concentrations. Furthermore, comparisons of global warming potentials between two simulations with and without CO₂ increase since 1960 reveal that the increased methane emission from the peatland could double the warming effects of the whole catchment by 2080 in the absence of CO₂ fertilization of the vegetation. This is the first process-based model study of the temporal evolution of a catchment-level carbon budget at high spatial resolution, integrating comprehensive and diverse fluxes including both terrestrial and aquatic carbon. Though this study also highlights some limitations in modelling subarctic ecosystem responses to climate change including aquatic system flux dynamics, nutrient limitation, herbivory and other disturbances and peatland expansion, our application provides a mechanism to resolve the complexity of carbon cycling in subarctic ecosystems while simultaneously pointing out the key model developments for capturing complex subarctic processes.
  • This discussion paper has been under review for the journal Biogeosciences (BG). Please refer to the corresponding final paper in BG. The published article is copyrighted by the author(s) and published by Copernicus Publications on behalf of the European Geosciences Union. The final revised paper is available at: http://hdl.handle.net/1957/56947
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  • Tang, J., Miller, P. A., Persson, A., Olefeldt, D., Pilesjö, P., Heliasz, M., ... & Christensen, T. R. (2015). Carbon budget estimation of a subarctic catchment using a dynamic ecosystem model at high spatial resolution. Biogeosciences, 12, 933-980. doi:10.5194/bgd-12-933-2015
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  • 12
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  • P. A. Miller acknowledges financial support from the ADSIMNOR (Advanced Simulation of Arctic Climate and Impact on Northern Regions) project funded by FORMAS (Swedish Research Council), and the Lund University Centre for the study of Climate and Carbon Cycle (LUCCI) funded by VR. The study is a contribution to the strategic research area Modelling the Regional and Global Earth System (MERGE), the Nordic Centre of Excellence DEFROST and the EU PAGE21 project. T. V. Callaghan and T. R. Christensen wish to thank FORMAS for funding for the project "Climate change, impacts and adaptation in the sub-Arctic: a case study from the northern Swedish mountains" (214-2008-188) and the EU Seventh Framework Programme infrastructure project "INTERACT" (http://www.eu-interact.org/).
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