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.
2001
Authors
Rolf D. Vogt E.T. Gjessing Dag Olav Andersen Nicholas Clarke T.C. Gadmar K. Bishop U.S. Lundström Michael StarrAbstract
In the Total Organic Carbon (TOC) intercalibration sub-project a set of 10 synthetic and natural samples as well as non-labile reverse osmosis isolates were sent to 25 laboratories for the analysis of TOC and dissolved Organic Carbon (DOC).The outcome of the statistical treatment of the results from this intercalibration and the information regarding the participants instruments and standard operational procedures is that:Synthetic samples provide apparent better precision than natural samples. This fact, together with the good experience from the use of non-labile Reverse Osmosis (RO) and freeze dried isolates of dissolved organic carbon (DOM) in the intercalibration, lead us to recommend the use of RO isolates as material for the preparation of house standards and for determination of methods merits.The intra laboratory precision (relative standard deviation) varied from 5 to 16%.The fractionation of the DOC by 0.45um membrane filtering causes in some cases a contamination of carbon to the sample.A specific construction in a brand of the TOC analysers give poor results in samples with high TOC concentrations and that are of refractory material. The five selected sampling sites have proven, on the basis of their soil and water chemistry, to be well suited for studying the effect of climate and S-deposition on the characteristics of DOM. 163 water samples from two seasons (fall and spring) and 20 soil samples are collected and analysed.Most water samples are determined for all major charge contributing species, DOM fractions, and several other parameters. The DOM in the surface waters have been isolated both using reverse osmosis and hydrophobic resin (XAD8). The original surface water, reconstructed water by RO isolates as well as the XAD8 fractionated DOM have been characterized by a number of methods ranging from optical properties to pH and metal titration.The RO isolates have been provided to 14 scientific research groups in Europe and North America that are in the process of using their analytical technique to characterize the DOM.The soils have been determined for key explanatory variables as pH, cation exchange capacity and C/N ratio. The main findings from the characterisation of DOM is that:Generally the hydrophobic acid fraction (HPO-A) was the main DOM fractions in all water compartments and sites.Seasonal variation in the DOM fractionation is found to be greater than the variation between the sites and water compartments. The DOM fractionation is therefore not a fingerprint of the site.According to a batch titration experiment the aluminium complexing ability of the HPO-A and hydrophilics (HPI) DOM fractions (fractionated using only the XAD8 resin) was indistinguishable.The HPI fraction has generally a higher site density of weak acids (WA).The reverse osmosis (RO) isolates represent the total DOM in the original sample.NMR spectres of the RO isolates show that the main difference between the sites lie in the amounts of carbohydrates and aromatic compounds.The RO isolates produce reconstructed water with DOM that have similar optical properties.PCA analysis suggest that as the S-deposition is decreasing we should expect relatively more hydrophobic character of the DOM.The spring sample from Svartberget differs from the rest of the samples in that there was a small rainstorm causing a hydrologic episode during the sampling. This led to the lowest pH, highest TOC and organic charge (A-) among the surface water samples. In terms of DOM characteristics this temporal variation in flow regime led to the highest HPO-N DOM fractions, lowest intensity of the NMR spectre and low ash content and lower density of WA then expected. This expresses the importance of temporal variation during hydrologic episodes.
Authors
Rolf D. Vogt K. Bishop Nicholas Clarke T.C. Gadmar E.T. Gjessing Jan Mulder Michael Starr Dag Olav AndersenAbstract
The main tasks of the NOMiNiC project (Natural Organic Matter in the Nordic countries; see http://www.kjemi.uio.no/envir/nominic/) is to study the physiochemical characteristics of dissolved organic matter (DOM) and provide reverse osmosis (RO) spring and fall isolates of surface water natural organic matter (NOM) from 5 Nordic forested sites that differ mainly in atmospheric S-loading and climate. Hydrophobic and hydrophilic fractions are hypothesized to be more easily defined and have distinct different chemical characteristics than the total sample. A XAD-8 fractionation may then be used as a simple proxy for the physico-chemical properties of NOM. Both XAD-8 fractions and the total DOM sample have been base and metal titrated. Enhanced understanding of the significance of the numerous operationally defined parameters describing NOM will be achieved through a common multi-dimensional characterisation of the same set of isolates, that span a large spectre of the variation found in DOM. 7 institutes are already collaborating in characterizing the RO isolates using a large range of techniques and new participants are invited. In this presentation the 5 sampling sites are described and some results of the characterisation of the RO isolates are presented.
2000
Abstract
No abstract has been registered
Authors
Jan Mulder J.F. Gallardo Lancho E. Matzner Edward Tipping Charlotte Bryant Nicholas Clarke S. Lofts B. Michalzik A. Vicente EstebanAbstract
No abstract has been registered
Abstract
Nitrogen is among the most important plant nutrients, and the effects on forest trees of changes in the concentrations and fluxes of both inorganic and organic nitrogen need to be known. In Norway, much of the nitrogen present in natural waters is organic (Mulder et al., 2000), therefore this fraction can not be neglected. Work using glycine has shown that forest plants can take up some forms of organic nitrogen directly, without preliminary mineralisation (Nsholm et al., 1998).Amino acids and amino sugars appear to be the most important organic sources of nitrogen for plants, including Norway spruce (Picea abies (L.) Karst.) (Johnsson et al., 1999). Organic nitrogen occurs in different forms. In soils, the most important are heterocyclic compounds and amino acids (35 % and 40 % respectively, Schulten and Schnitzer, 1998). In soil waters, amino sugars may also be important (Michalzik and Matzner, 1999).At present, organic nitrogen is normally determined as the difference between total nitrogen and the sum of nitrogen in nitrate and ammonium. This is not entirely satisfactory, as there will be a certain amount of uncertainty in each of the three determinations required. The total uncertainty involved in the determination of organic nitrogen may then be quite large compared to the actual concentration, especially when most nitrogen is present as inorganic nitrogen.A method for the direct determination of organic nitrogen is therefore desirable. Because organic nitrogen generally has a higher molecular weight than inorganic nitrogen, it might be possible to separate organic from inorganic nitrogen using size fractionation methods. In 1998, we worked on the setting up of methods for the determination of amino acids and amino sugars in soil waters, and on the direct determination of organic nitrogen using equilibrium dialysis.
Abstract
No abstract has been registered
1999
Authors
Jan Mulder J.F. Gallardo E. Matzner Edward Tipping Charlotte Bryant Nicholas Clarke S. Lofts B. Michalzik M.A. VicenteAbstract
No abstract has been registered
Abstract
DOC concentrations in soil water in podzols decreased from median values of 37 and 39 mg/l in the F and H layers, respectively, to about 6 mg/l in the B horizon. The decrease was most pronounced in the mineral soil. An increase in concentrations was found in the surface soils in late summer and autumn, apparently due in large part to increased production, which took place in both the canopy and the forest floor, although evaporative concentration of soil water could also have been partially responsible. In the B horizon, increased concentrations of DOC could be observed in the autumn, although these increases were much lower than for the surface horizons. A correlation was found between the surface soil DOC concentrations and the mean surface soil temperature 1 to 2 months previously, which could be due to the buffering effect of sorption processes. However, the increase in the net amount leached could not be clearly attributed to increased temperature. In the autumn, concentrations did not decline immediately when temperature decreased, which may be due to leaching of previously adsorbed organic matter. During the autumn, concentrations of DOC in streams increased in periods of high discharge due to increased input of high-DOC surface soil water. At the same time, DOC concentrations in surface soil water largely decreased, presumably as DOC was washed out. An increase in DOC was not seen in periods of high discharge in the early spring. The highest concentrations of TOC (both with and without flux-weighting) at the weir were also found in the autumn). Correlation of TOC in streamwater with temperature was poor but, for the winter months, often significant. A positive correlation in the winter was probably associated with higher fluxes due to temperature-induced snowmelt. DON, which is the dominant form of dissolved nitrogen at all depths in the podzols at Birkenes, also decreased sharply in concentration in the mineral soil. However, there was an increase in the concentration of DON relative to DOC. The C/N ratio thus decreased downwards in the soil, indicating a possible preferential adsorption of N-poor DOC. Much of the DON in throughfall appeared to be of low molecular weight. This was not the case for DON in soil water.
1998
Abstract
No abstract has been registered
Abstract
No abstract has been registered