101 research outputs found
The ability of contrasting ericaceous ecosystems to buffer nitrogen leaching
Much attention has been given to the carbon balance of peatland and heathland ecosystems and their role as global carbon stores. They are also important as buffers for atmospheric nitrogen (N) pollution, locking N into the soil and vegetation through tight nutrient cycling and preventing the leaching of soluble N into freshwater ecosystems. We compared mean annual soil exchangeable N, mineralisation and soil solution nitrogen at three contrasting ericaceous-dominated ecosystems: a lowland heath, an upland heath and an ombrotrophic raised bog at intermediate altitude, all of which were sites of long-term N-manipulation experiments. We expected that soil leachate N would be associated with soil C/N and total soil C, and that sites with higher C % and soil C/N would have greater ability to buffer N deposition before N saturation and leaching began. However, although soil solution N responded to N deposition at all the sites, we found that only the heathland sites were consistent with this expectation. The bog, with the highest C/N and largest C pool, was not the most strongly buffered. The upland heath was most effective at retaining N (extractable NH4+-N +3900 % from control) compared to the lowland heath (extractable NH4+-N +370 % from control) and the bog (extractable NH4+-N, +140–240 % from control). We concluded that the absence of a definable Calluna litter layer at the lowland heath and the bog, and the anoxic conditions at the bog, explained the earlier onset of leaching and that carbon and nitrogen cycles appeared more closely coupled in the heathlands but became decoupled at the bog due to the strong controlling effect of hydrology
Experimental field estimation of organic nitrogen formation in tree canopies
The content of organic N has been shown in many studies to increase during the passage of rain water through forest canopies. The source of this organic N is unknown, but generally assumed to come from canopy processing of wet or dry-deposited inorganic N. There have been very few experimental studies in the field to address the canopy formation or loss of organic N. We report two studies: a Scots pine canopy exposed to ammonia gas, and a Sitka spruce canopy exposed to ammonium and nitrate as wet deposition. In both cases, organic N deposition in throughfall was increased, but only represented a small fraction (<10%) of the additional inorganic N supplied, suggesting a limited capacity for net organic N production, similar in both conifer canopies under Scottish summertime conditions, of less than 1.6 mmol Nm2 mth1 (equivalent to 3 kg N ha1 y1)
Real Time Turbulent Video Perfecting by Image Stabilization and Super-Resolution
Image and video quality in Long Range Observation Systems (LOROS) suffer from
atmospheric turbulence that causes small neighbourhoods in image frames to
chaotically move in different directions and substantially hampers visual
analysis of such image and video sequences. The paper presents a real-time
algorithm for perfecting turbulence degraded videos by means of stabilization
and resolution enhancement. The latter is achieved by exploiting the turbulent
motion. The algorithm involves generation of a reference frame and estimation,
for each incoming video frame, of a local image displacement map with respect
to the reference frame; segmentation of the displacement map into two classes:
stationary and moving objects and resolution enhancement of stationary objects,
while preserving real motion. Experiments with synthetic and real-life
sequences have shown that the enhanced videos, generated in real time, exhibit
substantially better resolution and complete stabilization for stationary
objects while retaining real motion.Comment: Submitted to The Seventh IASTED International Conference on
Visualization, Imaging, and Image Processing (VIIP 2007) August, 2007 Palma
de Mallorca, Spai
δ15N of lichens reflects the isotopic signature of ammonia source
Although it is generally accepted that δ15N in lichen reflects predominating N isotope sources in the environment, confirmation of the direct correlation between lichen δ15N and atmospheric δ15N is still missing, especially under field conditions with most confounding factors controlled. To fill this gap and investigate the response of lichens with different tolerance to atmospheric N deposition, thalli of the sensitive Evernia prunastri and the tolerant Xanthoria parietina were exposed for ten weeks to different forms and doses of N in a field manipulation experiment where confounding factors were minimized. During this period, several parameters, namely total N, δ15N and chlorophyll a fluorescence, were measured. Under the experimental conditions, δ15N in lichens quantitatively responded to the δ15N of released gaseous ammonia (NH3). Although a high correlation between the isotopic signatures in lichen tissue and supplied N was found both in tolerant and sensitive species, chlorophyll a fluorescence indicated that the sensitive species very soon lost its photosynthetic functionality with increasing N availability. The most damaging response to the different N chemical forms was observed with dry deposition of NH3, although wet deposition of ammonium ions had a significant observable physiological impact. Conversely, there was no significant effect of nitrate ions on chlorophyll a fluorescence, implying differential sensitivity to dry deposition versus wet deposition and to ammonium versus nitrate in wet deposition. Evernia prunastri was most sensitive to NH3, then NH4+, with lowest sensitivity to NO3−. Moreover, these results confirm that lichen δ15N can be used to indicate the δ15N of atmospheric ammonia, providing a suitable tool for the interpretation of the spatial distribution of NH3 sources in relation to their δ15N signal
Identification of potential “Remedies” for Air Pollution (nitrogen) Impacts on Designated Sites (RAPIDS)
Atmospheric nitrogen (N) deposition is a significant threat to semi-natural habitats and species in the UK, resulting in on-going erosion of habitat quality and declines in many species of high conservation value. The project focused on impacts and remedies for designated conservation sites, especially Natura 2000 sites protected under the EU Habitats Directive. However, the approach and certainly the measures could be equally applied to other areas of high conservation value. Evidence was drawn together to develop a framework for identifying key N threats at individual sites as a basis to target mitigation options in the context of potential legislative, voluntary and financial instruments
Synthesizing greenhouse gas fluxes across nine European peatlands and shrublands: responses to climatic and environmental changes
In this study, we compare annual fluxes of methane
(CH4), nitrous oxide (N2O) and soil respiratory carbon dioxide
(CO2) measured at nine European peatlands (n = 4) and
shrublands (n = 5). The sites range from northern Sweden
to Spain, covering a span in mean annual air temperature
from 0 to 16 �C, and in annual precipitation from 300 to
1300mmyr−1. The effects of climate change, including temperature
increase and prolonged drought, were tested at five
shrubland sites. At one peatland site, the long-term (>30 yr)
effect of drainage was assessed, while increased nitrogen deposition
was investigated at three peatland sites.
The shrublands were generally sinks for atmospheric CH4,
whereas the peatlands were CH4 sources, with fluxes ranging
from −519 to +6890 mgCH4-Cm−2 yr−1 across the studied
ecosystems. At the peatland sites, annual CH4 emission
increased with mean annual air temperature, while
a negative relationship was found between net CH4 uptake
and the soil carbon stock at the shrubland sites. Annual
N2O fluxes were generally small ranging from −14
to 42 mgN2O-Nm−2 yr−1. Highest N2O emission occurred
at the sites that had highest nitrate (NO−
3 ) concentration
in the soil water. Furthermore, experimentally increased
NO−
3 deposition led to increased N2O efflux, whereas prolonged
drought and long-term drainage reduced the N2O efflux.
Soil CO2 emissions in control plots ranged from 310
to 732 gCO2-Cm−2 yr−1. Drought and long-term drainage generally reduced the soil CO2 efflux, except at a hydric
shrubland where drought tended to increase soil respiration.
In terms of fractional importance of each greenhouse gas
to the total numerical global warming response, the change in
CO2 efflux dominated the response in all treatments (ranging
71–96 %), except for NO−
3 addition where 89% was due to
change in CH4 emissions. Thus, in European peatlands and
shrublands the effect on global warming induced by the investigated
anthropogenic disturbances will be dominated by
variations in soil CO2 fluxes
Beam-induced backgrounds measured in the ATLAS detector during local gas injection into the LHC beam vacuum
Inelastic beam-gas collisions at the Large Hadron Collider (LHC), within a few hundred metres of the ATLAS experiment, are known to give the dominant contribution to beam backgrounds. These are monitored by ATLAS with a dedicated Beam Conditions Monitor (BCM) and with the rate of fake jets in the calorimeters. These two methods are complementary since the BCM probes backgrounds just around the beam pipe while fake jets are observed at radii of up to several metres. In order to quantify the correlation between the residual gas density in the LHC beam vacuum and the experimental backgrounds recorded by ATLAS, several dedicated tests were performed during LHC Run 2. Local pressure bumps, with a gas density several orders of magnitude higher than during normal operation, were introduced at different locations. The changes of beam-related backgrounds, seen in ATLAS, are correlated with the local pressure variation. In addition the rates of beam-gas events are estimated from the pressure measurements and pressure bump profiles obtained from calculations. Using these rates, the efficiency of the ATLAS beam background monitors to detect beam-gas events is derived as a function of distance from the interaction point. These efficiencies and characteristic distributions of fake jets from the beam backgrounds are found to be in good agreement with results of beam-gas simulations performed with theFluka Monte Carlo programme
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