Publications
NIBIOs employees contribute to several hundred scientific articles and research reports every year. You can browse or search in our collection which contains references and links to these publications as well as other research and dissemination activities. The collection is continously updated with new and historical material.
2018
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Authors
Ingeborg KlingenAbstract
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Inga Marie Aasen Ingrid Sandbakken Rasa Slizyte Michael Roleda Jorunn Skjermo Åshild KrogdahlAbstract
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Abstract
Freezing and thawing have large effects on water flow in soils since ice may block a large part of the pore space and thereby prevent infiltration and flow through the soil. This, in turn, may have consequences for contaminant transport. For example, transport of solutes contained at or close to the soil surface can be rapidly transported through frozen soils in large pores that were air filled at the time of freezing. Accounting for freezing and thawing could potentially improve model predictions used for risk assessment of contaminant leaching. A few numerical models of water flow through soil accounts for freezing by coupling Richards’ equation and the heat flow equation using of the generalized Clapeyron equation, which relates the capillary pressure to temperature during phase change. However, these models are not applicable to macroporous soils. The objective of this study was to develop and evaluate a dual-permeability approach for simulating water flow in soil under freezing and thawing conditions. To achieve this we extended the widely used MACRO-model for water flow and solute transport in macroporous soil. Richards’ equation and the heat flow equation were loosely coupled using the Clapeyron equation for the soil micropore domain. In accordance with the original MACRO model, capillary forces were neglected for the macropore domain and conductive heat flow in the macropores was not accounted for. Freezing and thawing of macropore water, hence, were solely governed by heat exchange between the pore domains. This exchange included a first-order heat conduction term depending on the temperature difference between domains and the diffusion pathlength (a proxy variable related to the distance between macropores) and convective heat flow. As far as we know, there are no analytical solutions available for water flow during freezing and thawing and laboratory data is limited for evaluation of water flow through macropores. In order to evaluate the new model approach we therefore first compared simulation results of water flows during freezing for the micropore domain to existing literature data. Our model was shown to give similar results as other available models. We then compared the first-order conductive heat exchange during freezing to a full numerical solution of heat conduction. Finally, simulations were run for water flow through frozen soil with initially air-filled macropores for different boundary conditions. Simulation results were sensitive to parameters governing the heat exchange between pore domains for both test cases.
Authors
Anto Raja Dominic Ole Martin Eklo Marianne Stenrød Eivind Solbakken Roar Lågbu Peter Horney Burkhard Golla Jörn StrassemeyerAbstract
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Authors
Ingeborg KlingenAbstract
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Authors
Kris Verheyen Martin Bažány Ewa Chećko Markéta Chudomelová Déborah Closset-Kopp Patryk Czortek Guillaume Decocq Pieter De Frenne Luc De Keersmaeker Cecilia Enriquez Garcia Martina Fabšičová John-Arvid Grytnes Lucia Hederová Radim Hédl Thilo Heinken Fride Høistad Schei Soma Horváth Bogdan Jaroszewicz Edyta Jermakowicz Terezá Klinerova Jens Kolk Martin Kopecký Iwona Kuras Jonathan Lenoir Martin Macek František Máliš Tone Constance Martinessen Tobias Naaf László Papp Ágnes Papp-Szákaly Paweł Pech Petr Petřík Jindřich Prach Kamila Reczýnska Magne Sætersdal Fabien Spicher Tibor Standovár Krzysztof Świerkosz Ewa Szczęśniak Zoltán Tóth Karol Ujházy Mariana Ujházyová Pieter Vangansbeke Ondřej Vild Dan Wołkowycki Monika Wulf Lander BaetenAbstract
Aim: Revisits of non-permanent, relocatable plots first surveyed several decades ago offer a direct way to observe vegetation change and form a unique and increasingly used source of information for global change research. Despite the important insights that can be obtained from resurveying these quasi-permanent vegetation plots, their use is prone to both observer and relocation errors. Studying the combined effects of both error types is important since they will play out together in practice and it is yet unknown to what extent observed vegetation changes are influenced by these errors. Methods: We designed a study that mimicked all steps in a resurvey study and that allowed determination of the magnitude of observer errors only vs the joint observer and relocation errors. Communities of vascular plants growing in the understorey of temperate forests were selected as study system. Ten regions in Europe were covered to explore generality across contexts and 50 observers were involved, which deliberately differed in their experience in making vegetation records. Results: The mean geographic distance between plots in the observer+relocation error data set was 24 m. The mean relative difference in species richness in the observer error and the observer+relocation data set was 15% and 21%, respectively. The mean “pseudo-turnover” between the five records at a quasi-permanent plot location was on average 0.21 and 0.35 for the observer error and observer+relocation error data sets, respectively. More detailed analyses of the compositional variation showed that the nestedness and turnover components were of equal importance in the observer data set, whereas turnover was much more important than nestedness in the observer+relocation data set. Interestingly, the differences between the observer and the observer+relocation data sets largely disappeared when looking at temporal change: both the changes in species richness and species composition over time were very similar in these data sets. Conclusions: Our results demonstrate that observer and relocation errors are nonnegligible when resurveying quasi-permanent plots. A careful interpretation of the results of resurvey studies is warranted, especially when changes are assessed based on a low number of plots. We conclude by listing measures that should be taken to maximally increase the precision and the strength of the inferences drawn from vegetation resurveys.