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  • 1
    Electronic Resource
    Electronic Resource
    The fate of 15N added to high Arctic tundra to mimic increased inputs of atmospheric nitrogen released from a melting snowpack (2005)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 11 (2005), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Increases in the long-range aerial transport of reactive N species from low to high latitudes will lead to increased accumulation in the Arctic snowpack, followed by release during the early summer thaw. We followed the release of simulated snowpack N, and its subsequent fate over three growing seasons, on two contrasting high Arctic tundra types on Spitsbergen (79°N). Applications of 15N (99 atom%) at 0.1 and 0.5 g N m−2 were made immediately after snowmelt in 2001 as either Na15NO3 or 15NH4Cl. These applications are approximately 1 × and 5 × the yearly atmospheric deposition rates. The vegetation at the principal experimental site was dominated by bryophytes and Salix polaris while at the second site, vegetation included bryophytes, graminoids and lichens. Audits of the applied 15N were undertaken, over two or three growing seasons, by determining the amounts of labeled N in the soil (0–3 and 3–10 cm), soil microbial biomass and different vegetation fractions.Initial partitioning of the 15N at the first sampling time showed that ∼60% of the applied 15N was recovered in soil, litter and plants, regardless of N form or application rate, indicating that rapid immobilization into organic forms had occurred at both sites. Substantial incorporation of the 15N was found in the microbial biomass in the humus layer and in the bryophyte and lichen fractions. After initial partitioning there appeared to be little change in the total 15N recovered over the following two or three seasons in each of the sampled fractions, indicating highly conservative N retention. The most obvious transfer of 15N, following assimilation, was from the microbial biomass into stable forms of humus, with an apparent half-life of just over 1 year. At the principal site the microbial biomass and vascular plants were found to immobilize the greatest proportion of 15N compared with their total N concentration. In the more diverse tundra of the second site, lichen species and graminoids competed effectively for 15NH4-N and 15NO3-N, respectively. Results suggest that Arctic tundra habitats have a considerable capacity to immobilize additional inorganic N released from the snow pack. However, with 40% of the applied 15N apparently lost there is potential for N enrichment in the surrounding fjordal systems during the spring thaw.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2486.2005.01044.x
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  • 2
    Electronic Resource
    Electronic Resource
    Speciation and solubility of Cu, Ni and Pb in contaminated soils (2004)
    Oxford, UK; Malden, USA : Blackwell Publishing Ltd/Inc.
    European journal of soil science 55 (2004), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: A long-term incubation experiment was established to assess the solid ⇅ solution equilibria of (Cu2+), (Pb2+) and (Ni2+) in soil pore water. The experiment comprised 23 soils spiked with 135, 300 and 75 mg kg−1 of Cu, Pb and Ni, respectively, added as nitrate salts in solution. Samples of soil pore water were extracted several times during the incubation period of 818 days and concentrations of Cu, Pb, Ni, dissolved organic carbon and major cations and anions were measured. Similar measurements were carried out on a smaller selection of historically contaminated soils to extend the range of data and assess compatibility of the measurements with the incubated soils. The chemical speciation program ‘WHAM VI’ was used to speciate metal ions in solution. A pH-dependent Freundlich equation was used to describe free ion activities, p(M2+), for Cu, Pb and Ni using total adsorbed metal, soil pH, soil organic carbon content and ionic strength as determining variables. For all three metals the greatest improvements in model fit were found when metal ions were assumed to be adsorbed exclusively on soil organic carbon rather than on the ‘whole soil’. Further improvements in the description of p(Cu2+) and p(Ni2+) were found when the ionic strength of the soil pore water was included within the model formulation. Residual standard deviations (–log10(M2+) units) for the best-fit models were 0.36, 0.53 and 0.29 for p(Cu2+), p(Pb2+) and p(Ni2+), respectively. The effects of progressive fixation of Pb, Cu and Ni on model parameterization, during the course of the experiment, were found to be small. Independent datasets from both published and unpublished sources were used to compare experimental protocols and validate the model for the determination of (M2+) in soil pore water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2389.2004.00627.x
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  • 3
    Electronic Resource
    Electronic Resource
    The use of dietary calcium intake of dairy ruminants to predict the transfer coefficient of radiostrontium to milk (1997)
    Springer
    Radiation and environmental biophysics 36 (1997), S. 39-43 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Transfer coefficients (the equilibrium ratio be-tween radionuclide activity concentration in milk or meat and the daily intake of radionuclide) are widely used to predict the contamination of animal products following the release of radionuclides into the environment. For a transfer coefficient to be generally applicable, its value must be constant for a range of circumstances. However, this is not the case for radiostrontium, the behaviour of which is strongly influenced by that of the homeostatically controlled nutrient, calcium. In this study, a relationship is derived between radiostrontium transfer coefficients and dietary calcium intake which takes into account the observed ratio for strontium:calcium transfer to milk. This relationship is tested against a range of observed data collated from the literature (n = 30) and found to account for 93% of the variability in transfer coefficient values. Model calculations show that a reduction in F m of at least 40%–60% would be expected if dairy cattle, fed rations typical for well-managed herds, were supplemented with 100–200 g per day. Larger reductions would be predicted when dietary calcium intake is low.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050053
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  • 4
    Electronic Resource
    Electronic Resource
    A metabolic approach to simulating the dynamics of C-14, H-3 and S-35 in sheep tissues (1998)
    Springer
    Radiation and environmental biophysics 36 (1998), S. 243-250 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The results of a study in which groups of sheep were given single oral administrations of 14C, 3H and 35S and then slaughtered over a period of 1 year are reported. The experimental data were used to investigate the potential of metabolically based models for describing the transfer of the three radionuclides to sheep tissues. The structure of these models is based upon a simplified understanding of the transfer of the macro-elements C, H and S by processes such as respiration and protein synthesis/degradation. A consequence of this approach is that the three models have many common parameters. The models reproduced the general trends of the observations, accounting for 74%, 66%, and 58% of the observed variation in the 14C, 3H and 35S data, respectively, suggesting that they may provide a useful alternative approach to modelling the transfer of these radionuclides. The models presented are limited to the particular experimental situation for which they were developed, and further experimental work would be required to extend them. However, such metabolically based models have great potential: for example, they should be able to account for the influence of dietary intake, physiological status or the form of the radionuclide in the animals diet (e.g. tritiated water or organically bound tritium).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050078
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  • 5
    Electronic Resource
    Electronic Resource
    Variation in the metabolism of radiocaesium between individual sheep (1998)
    Springer
    Radiation and environmental biophysics 37 (1998), S. 277-281 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Considerable variability has been recorded in the radiocaesium activity concentration of muscle between individual sheep in the same flocks in upland areas that received fallout from the Chernobyl accident. In a previous paper we demonstrated that there is a propensity for certain sheep within a flock to be always amongst the most contaminated and others to be consistently the least contaminated. Here we report a study to determine the extent to which variation in the metabolism of radiocaesium by individual sheep may contribute to the observed variability within sheep flocks. The transfer coefficient and biological half-life of orally administered ionic radiocaesium in muscle were determined under controlled conditions in 22 ewes from an upland farm in an area of the UK which received comparatively high levels of Chernobyl fallout. There was considerable variation between individuals in both the transfer coefficient (0.19–0.56 day⋅kg–1; mean 0.34 day⋅kg–1) and biological half-life in muscle (5.2– 18.7 days; mean 9.8 days). Changes in liveweight during the study and feed intake together accounted for 72% of the variation in the derived transfer coefficients; liveweight change also accounted for 56% of the observed variation in biological half-life. In a subsequent study, the true absorption coefficient of radiocaesium was determined in 12 of the ewes. There was a positive correlation between transfer and true absorption coefficients (R=0.57). We conclude that differences in the metabolism of radiocaesium will contribute to the observed variability in radiocaesium activity concentrations within sheep flocks in areas which were contaminated by Chernobyl fallout. We also suggest that for growing animals, the influence of liveweight change and feed intake on radiocaesium transfer may be greater than observed here. Similarly, in dairy cattle, for which feed intake changes considerably during the course of a lactation, large temporal variation in radiocaesium transfer to milk could be expected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050129
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  • 6
    Electronic Resource
    Electronic Resource
    Generic relationship between calcium intake and radiostrontium transfer to the milk of dairy ruminants (1998)
    Springer
    Radiation and environmental biophysics 37 (1998), S. 129-131 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The hypothesis is tested that there is a generic relationship between the calcium intake and the transfer of radiostrontium to milk which can be used for all dairy ruminants. In addition to the daily calcium intake, the relationship also requires values for the strontium to calcium observed ratio, which describes the discrimination in transfer of the two elements to milk (a value of 0.11 is used), and the calcium concentration in milk. The relationship had previously only been validated for dairy cattle as there were insufficient data for other ruminant species. Here, we present recently available data for dairy goats, and also a limited amount of data for sheep derived from the literature. From the comparison between these data and predicted values, we conclude that it is possible to derive a generic model of the transfer of radiostrontium to the milk of dairy ruminants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004110050105
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  • 7
    Electronic Resource
    Electronic Resource
    Development and testing of a revised dynamic model of radiocaesium transfer to sheep tissues (1996)
    Springer
    Radiation and environmental biophysics 35 (1996), S. 19-24 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The model of radiocaesium transfer to sheep presented by Galer et al. [1] provides reliable predictions only for sheep of a similar body weight to those used in the development of the model (approximately 30 kg). To extend the applicability of the model, it was necessary to re-parameterise it in terms of activity concentrations in tissues rather than total activities within them (although for gut compartments the use of activity has been retained). The rate coefficients for the new model have been estimated by fitting the model to the data used by Galer et al. [1] which was derived from a single “calibration” experiment. The new model was found to account for 94% of the observed variation in the data (n=42), a result similar to that obtained by Galer et al. [1]. The model has also been tested against data not used in its development but obtained from four separate experiments undertaken by three different laboratories. Good agreement between the predictions of the new model and observations was found for most circumstances and for several breeds of sheep with different body weights. It is concluded that the new model provides a useful dynamic description of radiocaesium transfers to the tissues of sheep of different breeds and under different contamination scenarios.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01211238
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  • 8
    Electronic Resource
    Electronic Resource
    The tree-crop interface: representation by coupling of forest and crop process-models (1995)
    Springer
    Agroforestry systems 30 (1995), S. 199-221 
    Details
    ISSN: 1572-9680
    Keywords: agroforestry models ; crop models ; forest models ; root growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Three process-based approaches to agroforestry modelling are described. These are (a) coupling a continuous-canopy forest model (Hybrid) and tropical crop model (PARCH); (b) coupling an individual-tree model (MAESTRO) with a crop model (PARCH); and (c) incorporating a combined model of evaporation and radiation interception by neighbouring species (ERIN). The coupled Hybrid/PARCH was parameterised for maize and eucalyptus, and run in five contrasting weather-types. As expected, shade is the most important factor limiting yield in wet sites; water in dry sites. Year-to-year variability in crop yield is increased by light and water competition. MAESTRO/PARCH was run with similar assumptions, and gave comparable yield predictions, except at the driest site where it allows small areas distant from the tree sufficient water to produce a modest yield. Hybrid/PARCH predicted total crop failure in the same climate. Yields on drier sites were higher in the shade, but water competition was severe close to the tree. ERIN is simpler than the above models, but is unique in including the transfer of heat and water vapour between the two canopies. Transpiration from a moist understorey can humidify air in the overstorey, and reduce its transpiration; whilst a dry understorey will give off sensible heat, which increases the vapour pressure deficit in the overstorey and causes its transpiration to increase. Changes in overstorey transpiration due to fluxes from the understorey may approach 15–20%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00708921
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