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.
1999
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Torstein KvammeAbstract
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Jan Erik SundbyAbstract
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P.K. Egeberg Morten Eikenes E.T. GjessingAbstract
In Norwegian lakes, organic nitrogen typically constitutes about 60% of the total dissolved pool of nitrogen. However, evaluation of its effect on aquatic ecosystems and its role as promoter of heterotrophic growth in water distribution systems is difficult because of restricted knowledge about the various forms of organically-bound nitrogen in water. On line standard wet chemical analysis of total nitrogen was combined with high-performance size exclusion chromatographic (HPSEC) separation of natural organic matter (NOM) for investigation of the distribution of nitrogen between size classes of NOM. It was found that the high molecular weight (HMW) size fractions (humic acids) are enriched in nitrogen relative to the low molecular weight (LMW) size fractions (fulvic acids, nominal molecular weights of about 1000 Daltons) by a factor of up to 10. The low molecular weight size fractions (a few hundred Daltons) are interpreted to be of autocthonous origin based on their low C/N ratios, and correlation with the eutrophic status of the source waters. It was observed that NOM from water sources surrounded by large catchments contains relatively more nitrogen in HMW size fractions than NOM from small catchments, except that bog-derived NOM is particularly enriched in HMW nitrogen.
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David Clapham Ingegerd Dormling I. Ekberg G. Eriksson M. Qamaruddin D. Vince-PrueAbstract
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Jorunn Elisabeth OlsenAbstract
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M. AlvetegAbstract
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Peder GjerdrumAbstract
In pine, heart- and sapwood can in some respect be considered two different timber species, with divergent wood properties. The knowledge of their occurrence has thus been a task for wood scientists ever since the fundamental work of Pilz (1907) a century ago. Close to 1800 observations from all over Scandinavia are analysed. Conclusion is that the physiological conversion from sap- to heartwood in the living tree is under the sole control of time, i.e. years past since activity in the apical. Other factors (height in tree, tree or stand characteristics) seem to be without influence The prediction of heartwood amount in individual trees in a stand of known age is thus attainable. Accordingly, the estimation of age in a log cross-cut, and thus of mean annual ring width, is also feasible, once diameter and heartwood ratio is known. Experiments using IR photography indicate the potential of using such equipment in heartwood detection.