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4. Field-scale CH4 emission at a sub-arctic mire with heterogeneous permafrost thaw status.

Author

Lakomiec, Patryk, Holst, Jutta, Friborg, Thomas, Crill, Patrick, Rakos, Niklas, Kljun, Natascha, Olsson, Per-Ola, Eklundh, Lars, and RinneDepartment of Physical Geography and Ecosystem Science,Lund University, 223 62, Swedenjanne.rinne@nateko.lu.se, Janne

Subjects
TUNDRAS, PERMAFROST, SOIL moisture, THAWING, WESTERLIES, WATER table
Abstract

The Artic is exposed to faster temperature changes than most other areas on Earth. Constantly increasing temperature will lead to thawing permafrost and changes in the CH4 emissions from wetlands. One of the places exposed to those changes is the Abisko-Stordalen Mire in northern Sweden, where climate and vegetation studies have been conducted from the 1970s.In our study, we analyzed field-scale methane emissions measured by the eddy covariance method at Abisko-Stordalen Mire for three years (2014-2016). The site is a subarctic mire mosaic of palsas, thawing palsas, fully thawed fens, and open water bodies. A bimodal wind pattern prevalent at the site provides an ideal opportunity to measure mire patches with different permafrost statuses with one flux measurement system. The flux footprint for westerly winds is dominated by elevated palsa plateaus, while the footprint is almost equally distributed between palsas and thawing bog-like areas for easterly winds. As these patches are exposed to the same climatic conditions, we analyzed the differences in the responses of their methane emission for environmental parameters. The methane fluxes followed a similar annual cycle over the three study years, with a gentle rise during spring and a decrease during autumn and with no emission burst at either end of the ice-free season. The peak emission during the ice-free season differed significantly for the mire with two permafrost statuses: the palsa mire emitted 24 mg-CH4 m-2 d-1 and the thawing wet sector 56 mg-CH4 m-2 d-1. Factors controlling the methane emission were analyzed using generalized linear models. The main driver for methane fluxes was peat temperature for both wind sectors. Soil water content above the water table emerged as an explanatory variable for the three years for western sectors and the year 2016 in the eastern sector. Water table level showed a significant correlation with methane emission for the year 2016 as well. Gross primary production, however, did not show a significant correlation with methane emissions. Annual methane emissions were estimated based on four different gap-filing methods. The different methods generally resulted in very similar annual emissions. The mean annual emission based on all models was 4.2 ± 0.4 g- CH4 m-2 a-1 for western sector and 7.3 ± 0.7 g- CH4 m-2 a-1 for the eastern sector. The average annual emissions, derived from this data and a footprint climatology, were 3.6 ± 0.7 g-CH4 m-2 a-1 and 11 ± 2 g- CH4 m-2 a-1 for the palsa and thawing surfaces, respectively. Winter fluxes were relatively high, contributing 27-45 % to the annual emissions. [ABSTRACT FROM AUTHOR]

Published
2021
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6. Effects of molecular organization on exciton diffusion in thin films of bioinspired light-harvesting molecules.

Author

Laurens D. A. Siebbeles, Annemarie HuijserCurrent address: Department of Chemical Physics, Lund University, Box 124, S-22100 Lund, Swed, and Tom J. Savenije

Abstract

Efficient exciton diffusion in light-harvesting organic materials is of great importance for the development of cheap and flexible photovoltaic devices. Bioinspired molecular materials such as derivatives of phthalocyanine and porphyrin offer promising prospects for the realization of efficient exciton diffusion. The chemical composition of these molecules is found to strongly affect the molecular organization in thin films and in turn the efficiency of exciton diffusion. High singlet exciton diffusion coefficients exceeding 10−6m2s−1have been found. This value is similar to that for the natural chlorosomal bacterio-chlorophyll, which exhibits the highest exciton diffusion coefficient for self-assembled systems. [ABSTRACT FROM AUTHOR]

Published
2009
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7. Diffusion on complex networks: a way to probe their large-scale topological structures

Author

Simonsen, Ø</f>, Denmark, Astrup Eriksen, Ø</f>, Denmark##Department of Theoretical Physics, Lund University, Sölvegatan 14A, SE-223 62 Lund, Sweden, Maslov, Sergei, and Sneppen, Ø</f>, Denmark

Subjects
*DIFFUSION processes, *TOPOLOGY, *INTERNET, *COMPUTER networks
Abstract

A diffusion process on complex networks is introduced in order to uncover their large-scale topological structures. This is achieved by focusing on the slowest decaying diffusive modes of the network. The proposed procedure is applied to real-world networks like a friendship network of known modular structure, and an Internet routing network. For the friendship network, its known structure is well reproduced. In case of the Internet, where the structure is far less well known, one indeed finds a modular structure, and modules can roughly be associated with individual countries. Quantitatively, the modular structure of the Internet manifests itself in an approximately 10 times larger participation ratio of its slowest decaying modes as compared to the null model—a random scale-free network. The extreme edges of the Internet are found to correspond to Russian and US military sites. [Copyright &y& Elsevier]

Published
2004
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