335,480 research outputs found
Dissolved organic carbon and nitrogen leaching from Scots pine, Norway spruce and silver birch stands in southern Sweden
Full text linkThe effects of three common tree species – Scots pine, Norway spruce and silver birch – on leaching of dissolved organic carbon and dissolved nitrogen were studied in an experimental forest with podzolised soils in southern Sweden. We analyzed soil water collected with lysimeters and modeled water fluxes to estimate dissolved C and N fluxes. Specific UV absorbance (SUVA) was analyzed to get information about the quality of dissolved organic matter leached from the different stands. Under the O horizon, DOC concentrations and fluxes in the birch stands were lower than in the spruce and pine stands; annual fluxes were 21 g m-2 y-1 for birch and 38 g m-2 y-1 and 37 g C m-2 y-1 for spruce and pine, respectively. Under the B horizon, annual fluxes for all tree species ranged between 3 and 5 g C m-2 y-1, implying greater loss of DOC in the mineral soil in the coniferous stands than in the birch stands. We did not find any effect of tree species on the quality of the dissolved organic matter, as measured by SUVA, indicating that the chemical composition of the organic matter was similar in leachates from all three tree species. Substantial amounts of nitrogen was leached out of the soil profile at the bottom of the B horizon from the pine and birch stands, whereas the spruce stands seemed to retain most of the nitrogen in the soil. These differences in N leaching have implications for soil N budgets
Spatio-Temporal Monitoring and Modelling of Birch Pollen in Belgium
No full textAir quality is primordially affected by anthropogenic emissions and has a tremendous impact on human health with more than 6 million premature deaths worldwide in 2015 (Landrigan et al. in The Lancet Commission on pollution and health, 2017) [3]. Biogenic emissions of aerosols such as pollen also impact the human wellbeing. The industrialized world suffers from a global increase in the burden of allergic respiratory diseases. Air pollution can influence both allergens and allergic subjects by increasing the immune reaction, and/or by an intensified biogenic emissions. In Europe, a quarter of the population suffers from pollinosis, whereas in some countries the prevalence is over 40%. To date, pollen of various trees and grasses in Belgium are monitored by the Belgian Scientific Institute for Public Health (Sciensano) at five stations on a daily basis. This sparse sampling cannot cover the spatial representativeness of the airborne pollen. Chemistry Transport Models (CTM’s) are therefore an interesting tool to both quantify and forecast its spatial and temporal distribution. Here we show the results of the spatio-temporal modelled birch pollen over Belgium using the CTM SILAM. This model is driven by 2008 ECMWF meteorological data and a MACC-III birch tree fraction map showing the spatial distribution of potential pollen sources. Pollen modelling is based on the temperature degree days approach.</p
Comparison of energy-wood and pulpwood thinning systems in young birch stands
Full text linkIn early thinnings, a profitable alternative to pulpwood could be to harvest whole trees as energy-wood. In theoretical analyses, we compared the extractible volumes of energy-wood and pulpwood, and their respective gross values in differently aged stands of early birch thinnings at varying intensities of removal. In a parallel field experiment, we compared the productivity at harvest of either pulpwood or energy-wood, and the profitability when the costs of harvesting and forwarding were included. The theoretical analyses showed that the proportion of the total tree biomass removed as pulpwood increased with increasing thinning intensity and stem size. The biomass volume was 1.5–1.7 times larger than the pulpwood volume for a 13.9 diameter at breast height stand and 2.0–3.5 times larger for a 10.4 diameter at breast height stand. In the field experiment, the harvested volume per hectare of energy-wood was almost twice as high as the harvest of pulpwood. The harvesting productivity (trees Productive harvesting Work Time-hour−1) was 205 in the energy-wood and 120 in the pulpwood treatment. The pulpwood treatment generated a net loss, whereas the energy-wood treatment generated a net income, the average difference being €595 ha−1. We conclude that in birch-dominated early thinning stands, at current market prices, harvesting energy-wood is more profitable than harvesting pulpwood
Observations and modelling of birch pollen emission and dispersion from an isolated source
Full text linkThe occurrence of allergic diseases in western countries increased during the last decades due to
greater awareness towards a hygienic lifestyle. The hygiene hypothesis relates the reduced expo-
sure to microbial pollution to an underdevelopment of the immune system, which in turn favours
the development of allergies. In order to provide information to affected individuals on adequate
pre-emptive measures, numerous studies on the health impact of allergenic pollen focus on their
atmospheric abundance and dispersion, including observations and simulation of emission and
transport. Prognostic models for the spatial distribution and concentration of different pollen
species on a regional scale are operational in many countries in order to identify highly affected
regions and allow health offices to announce warnings to the affected population. These models
are capable of predicting long-range transport in a full spatial resolution with respect to meteoro-
logical conditions. However, the initial abundance of airborne pollen in the models is determined
with empirically derived emission parameters, which are mostly based on long-term observation
averages with respect to large areas.
Field measurements and modelling work conducted in the framework of this thesis aimed at de-
scribing the emission and dispersion characteristics of an isolated natural birch pollen source in the
micro-scale, in order to improve the accuracy of the emission part in prognostic pollen transport
models. The basic approach was to infer the emission of the pollen source from downwind obser-
vations, with respect to meteorological conditions, by reproducing the observed pollen dispersion
with numerical simulations. Birch pollen are used, because they are among the most important
aeroallergens in Europe. In terms of quantifying the absolute pollen emission in speciffic cases,
however, the field observations of pollen concentrations were subject to various difficulties related
to sensor uncertainties and non-stationary conditions in the natural environment.
Firstly, the detailed investigation of pollen transport up- and downwind of the isolated source
relied on a large array of different instruments. In order to make the observations of birch pollen
concentrations comparable among different used instruments, a substantial part of this thesis is
dedicated to the description of performance and uncertainty of different pollen sampling methods.
Secondly, since naturally emitted pollen are used for tracers, instead of a controlled release of
artifficial particles, the observed pollen concentration can be biased by natural background con-
centration, which relates to emission from unknown sources upwind of the experiment site. The
wind
ow directed towards the birch canopy is substantially disturbed by its roughness and, addi-
tionally, a certain amount of airborne pollen is filtered by its vegetation elements. Observations
of undisturbed concentrations upwind of the windbreak thus fall short of describing the complex
pattern of downwind distribution. A computational
uid dynamics model, therefore, is used to
simulate Lagrangian-based trajectories of the pollen with respect to the disturbance of the wind
field. The results indicate that the portion of background concentration in the observed downwind
concentration is largely dependent on effects of accumulation due to deceleration of the wind
ow.
Deposition within the birch canopy is accounted for in a separate model, which is based on the
optical porosity of the windbreak. A combination of the two model approaches allows to eliminate
the portion of background concentration from the measured downwind concentrations, providing
information on the emissivity of the isolated birch pollen source.
Based on the corrected concentrations downwind of the windbreak, i.e. un-biased by background
concentration, a method of estimating the source strength of the isolated pollen source with a
Lagrangian particle model is assessed
MicroPoem: experimental investigation of birch pollen emissions
Full text linkDiseases due to aeroallergens constantly increased over the last decades and affect more and more people. Adequate protective and pre-emptive measures require both reliable assessment of production and release of various pollen species, and the forecasting of their atmospheric dispersion. Pollen forecast models, which may be either based on statistical knowledge or full physical transport and dispersion modeling, can provide pollen forecasts with full spatial coverage. Such models are currently being developed in many countries. The most important shortcoming in these pollen transport systems is the description of emissions, namely the dependence of the emission rate on physical processes such as turbulent exchange or mean transport and biological processes such as ripening (temperature) and preparedness for release. Thus the quantification of pollen emissions and determination of the governing mesoscale and micrometeorological factors are subject of the present project MicroPoem, which includes experimental field work as well as numerical modeling. The overall goal of the project is to derive an emission parameterization based on meteorological parameters, eventually leading to enhanced pollen forecasts. In order to have a well-defined source location, an isolated birch pollen stand was chosen for the set-up of a ‘natural tracer experiment', which was conducted during the birch pollen season in spring 2009. The site was located in a broad valley, where a mountain-plains wind system usually became effective during clear weather periods. This condition allowed to presume a rather persistent wind direction and considerable velocity during day- and nighttime. Several micrometeorological towers were operated up- and downwind of this reference source and an array of 26 pollen traps was laid out to observe the spatio-temporal variability of pollen concentrations. Additionally, the lower boundary layer was probed by means of a sodar and a tethered balloon system (also yielding a pollen concentration profile). In the present contribution a project overview is given and first results are presented. An emphasis is put on the relative performance of different sample technologies and the corresponding relative calibration in the lab and the field. The concentration distribution downwind of the birch stand exhibits a significant spatial (and temporal) variability. Small-scale numerical dispersion modeling will be used to infer the emission characteristics that optimally explain the observed concentration patterns
Betula papyrifera: paper birch, western birch, white birch, canoe birch
No full textSpecies profile for Betula papyrifera: paper birch, western birch, white birch, canoe birc
Larval parasitism of the autumnal moth reduces feeding intensity on the mountain birch
No full textPlants respond to grazing by herbivorous insects by emitting a range of volatile organic compounds, which attract parasitoids to their insect hosts. However, a positive outcome for the host plant is a necessary precondition for making the attraction beneficial or even adaptive. Parasitoids benefit plants by killing herbivorous insects, thus reducing future herbivore pressure, but also by curtailing the feeding intensity of the still living, parasitised host. In this study, the effect of parasitism on food consumption of the 5th instar larvae of the autumnal moth (Epirrita autumnata) was examined under laboratory conditions. Daily food consumption, as well as the duration of the 5th instar, was measured for both parasitised and non-parasitised larvae. The results showed that parasitism by the solitary endoparasitoid Zele deceptor not only reduced leaf consumption significantly but also hastened the onset of pupation in autumnal moth larvae. On the basis of the results, an empirical model was derived to assess the affects on the scale of the whole tree. The model suggests that parasitoids might protect the tree from total defoliation at least at intermediate larval densities. Consequently, a potential for plant–parasitoid chemical signalling appears to exist, which seems to benefit the mountain birch (Betula pubescens ssp. czerepanovii) by reducing the overall intensity of herbivore defoliation due to parasitism by this hymenopteran parasitoid
Spatio-temporal monitoring and modelling of birch pollen levels in Belgium
No full textIn Belgium, ~ 10% of the people is estimated to suffer from allergies due to pollen emitted by the birch family trees. Timely information on forthcoming pollen exposure episodes using a forecasting system can allow patients to take preventive measures. To date, the only available information on pollen concentrations in Belgium comes from five stations that monitor daily airborne birch pollen concentrations, but real-time and detailed spatial information is lacking. Pollen transport models can both quantify and forecast the spatial and temporal distribution of airborne birch pollen concentrations if accurate and updated maps of birch pollen emission sources are available and if the large inter-seasonal variability of birch pollen is considered. Here we show that the SILAM model driven by ECMWF ERA5 meteorological data is able to determine airborne birch pollen levels using updated maps of areal fractions of birch trees, as compared to the pollen observations of the monitoring stations in Belgium. Forest inventory data of the Flemish and Walloon regions were used to update the default MACCIII birch map. Spaceborne MODIS vegetation activity combined with an updated birch fraction map and updated start and end dates of the birch pollen season were integrated into SILAM. The correlation (R2) between SILAM modelled and observed time series of daily birch pollen levels of 50 birch pollen seasons increased up to ~ 50%. The slopes of the linear correlation increased on average with ~ 60%. Finally, SILAM is able to capture the threshold of 80 pollen grains m−3 exposure from the observations.</p
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