Publikasjoner
NIBIOs ansatte publiserer flere hundre vitenskapelige artikler og forskningsrapporter hvert år. Her finner du referanser og lenker til publikasjoner og andre forsknings- og formidlingsaktiviteter. Samlingen oppdateres løpende med både nytt og historisk materiale. For mer informasjon om NIBIOs publikasjoner, besøk NIBIOs bibliotek.
2003
Sammendrag
An individual-based agent model is presented which resembles aspects of natural evolution in ecosystems under selective pressure due to limited resources. The environmental conditions are determined by spatial and temporal variability of resource abundances.The agents have to choose between three different types of resources; the one consumed most during lifetime solely counts for the fitness of the individual agent. Simulation runs show that populations specialized in different resource types are mutually influencing each other under temporal variation of a single resource type.Mobility of agents in a locally heterogenous world enables recolonization after a population has starved to death. Wavelet analysis of the population time series reveals that some observed population dynamics show phenomena such as localized periodicities which cannot be explained by linear dependencies on the resource input dynamics.
Sammendrag
Modern information technology allows the investigation of the characteristic properties of living systems from a new perspective. Which of the ecosystem features are necessary conditions resulting from their constraints, which are accidental, constituting contingent facts of their respective histories?As long as we know of a single phylogenetic tree in nature, the difference is hard to tell, rendering the reconstruction and realisation of artificial ecologies a major challenge. It has been taken up by the high technology of the time since decades; since two decades, IT is leading in this respect.Are there life forms that can be created in contemporary computers, and which ones? Successes and failures of a number of virtualizations are forming de facto constraints for theoretical ecosystem research. Artificial Life (AL) research appears to be not just another attempt towards realistic models for ecological systems, but undermines the basic assumptions of most of conventional modeling in this area: in AL, behavior is in general irreducible to internal mechanisms; behavior results rather from interactive and intentional usage of the simulation.We try to elucidate and demonstrate the crucial role of interaction in these simulations, drawing from current developments in theoretical computer science as well as a number of examples. We propose a new classification of ecosystem models according to its degree of interactivity.
2002
Sammendrag
Concentrations and fluxes of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON), together with pools of carbon and nitrogen in the soil and biomass, were determined along north-south and east-west transects across Norway, Sweden and Finland. The data were analysed statistically and modelled using the mechanistic model DyDOC.Concentrations of DOC and DON were greatest in the O horizon and decreased downwards in the soil. The highest production of dissolved organic matter appears to take place in the O horizon and any contribution from thoroughfall is probably small. A pronounced seasonal effect with peak DOC concentrations in late summer/early autumn may be due to a seasonal (largely temperature) effect on DOC production.The effect of acidic precipitation upon DOC concentrations and fluxes was unclear. DOC in the O horizon was mostly of recent origin, while DOC in the B horizon appeared to include some older material, possibly desorbed from the soil. A positive correlation was found with electrical conductivity and a negative correlation with pH in DOC concentrations from the O horizon.A lack of correlation between DOC concentrations and temperature is probably due to a time lag between peak temperatures and peak DOC concentrations. Modelling of DOC concentrations and fluxes using DyDOC gave rasonable results, suggesting that it might be possible to use DyDOC as a general tool for modelling and forecasting DOC concentrations and fluxes in Nordic forest ecosytems.Scenario analysis using DyDOC suggested that increased temperature without increased litter input might result in increased production of CO2 rather than DOC. An increase in both temperature and litter input would lead to increased DOC concentrations, with possible implications for drinking water quality. Increased precipitation will lead to increased fluxes of DOC.
Forfattere
Nicholas ClarkeSammendrag
In natural waters, total organic carbon (TOC) is the sum of particulate and dissolved organic carbon. Dissolved organic carbon (DOC) is operationally defined, usually as organic carbon that passes through a 0.45 µm filter. Cellulose acetate or nitrate filters should not be used for this purpose due to contamination or adsorption problems. Glass fibre filters are preferable. Although the discussion below concerns DOC, much of it applies to TOC as well. Organic carbon is most often determined after oxidation to CO2 using combustion, an oxidant such as persulphate, UV or other high-energy radiation, or a combination of some of these. If only UV radiation with oxygen as oxidant is used, low DOC values may be obtained in the presence of humic substances. A variety of methods are used for detection, including infrared spectrometry, titration and flame ionization detection after reduction to methane. Always follow the instrument manufacturer’s instructions. For determination of dissolved organic carbon, dissolved inorganic carbon must be either removed by purging the acidified (for example with phosphoric acid) sample with a gas which is free from CO2 and organic compounds, or determined and subtracted from the total dissolved carbon. If acidification followed by purging is used, care should be taken as volatile organic compounds may also be lost. After acidification, remove CO2 by blowing a stream of pure carbon-free inert gas through the system for at least 5 minutes. Carbon is ubiquitous in nature, so reagents, water, and glassware cannot be completely cleaned of it. Method interferences (positive bias) may be caused by contaminants in the carrier gas, dilution water, reagents, glassware, or other sample processing hardware (for example a homogenization device). All of these materials must be routinely demonstrated to be free from interference under the conditions of analysis by running reagent blanks. Plastic bottles can bleed carbon into water samples, especially when they are new, or when they are used for low-level samples (less than 200 ppb C). Any new bottles (especially plastic) should ideally be filled with clean water for a period of several days or boiled in water for a few hours before use. The use of high purity or purified reagents and gases helps to minimise interference problems. It is very important to use ultra-pure water with a carbon filter or boiled distilled water just before preparing stock and standard solutions, in order to remove dissolved CO2. The stock solution should not be kept too long (about one week). For most DOC instruments a correction for DOC (due to dissolved CO2) in the dilution water used for calibration standards is necessary, especially for standards below 10 ppm C. The carbon in the blank should only be subtracted from standards and not from samples. For calibration, standard solutions are most often potassium hydrogen phthalate for total dissolved carbon and sodium bicarbonate for dissolved inorganic carbon. The DOC concentration should be within the working range of the calibration. If necessary the sample can be diluted. Sample DOC below about 50 ppb C can be affected by atmospheric exposure. In these cases, sampling bottles should be kept closed when possible, and autosampler vials should be equipped with septa for needle piercing by the autosampler.
Forfattere
Nicholas ClarkeSammendrag
Within ICP Forests, the question has arisen whether it is necessary to determine DOC or TOC in deposition. There are several possible reasons for doing so, which can be summarised under two headings: quality control and process studies.
Sammendrag
The project reported here was a co-operation between the National Focal Centers for four of the ICPs in Norway: ICP Mapping and Modeling, ICP Waters, ICP Forest and ICP Integrated Monitoring. Dynamic modeling was carried out using data from several sites in the ICP networks, with the aim of making predictions on the future acidification status for surface waters, forest and soils in Norway. Predictions are made for three different deposition scenarios. At two of the sites, the model predictions suggest that the Current Legislation scenario will not promote water qualities sufficient for sustainable fish populations, while the scenario seems sufficient for the others. Under the Maximum Feasible Reduction scenario one of the sites still will not reach a sufficiently high ANC. In general, the modeling results for forest soils agree with results from previous investigations stating that surface water acidification is more severe than the soil acidification. However, the results suggest that there has been soil acidification at all sites as a result of acid deposition and that the base saturation will not be built up again to pre-industrial levels during the next 50 years at any of the sites, not even with the Maximum Feasible Reduction Scenario.
Sammendrag
Det er ikke registrert sammendrag
Sammendrag
Det er ikke registrert sammendrag
Forfattere
O. Janne Kjønaas Isabella Børja Nicholas Clarke Heleen A. de Wit Lars Strand Hooshang MajdiSammendrag
Det er ikke registrert sammendrag
Sammendrag
The Norwegian intensive monitoring programme of forest condition has recorded rainfall, throughfall and soil water data from 1986 at 16 forest plots. Using covariance analysis, this study has examined short term and episodic influences on soil water ionic concentration at three of the plots, and identified both seasonal and long-term temporal trends. Acidity has decreased in bulk precipitation and throughfall, and the concentrations of base cations in the organic soil horizon have increased. Nevertheless, there is evidence of continued acidification in the organic and mineral soil horizons, though of a small scale. The influence of sea salt and drought effects on soil water chemistry are examined, but found to be unimportant in causing acidification effects such as increased soil aluminium concentration.