339 research outputs found
Exploding House Prices in Urban Housing Markets: Explanations and Policy Solutions for the Netherlands
Evaluating the SWAT model to predict streamflow, nitrate loadings and crop yields in a small agricultural catchment
This study aimed to evaluate the applicability of the Soil and Water
Assessment Tool (SWAT) to predict streamflow, nitrate loadings and crop
yields for a small agricultural catchment in northeastern Germany. To this
end, a 167 ha catchment was delineated consisting of 10 hydrological
response units. Daily data for streamflow and nitrate loadings from 2004 to
2015 were used to calibrate and validate the model, while annual values for
crop yields (winter wheat, winter barley, rapeseed, maize silage) were
available. In addition, the detailed field maps provided by the local farmer
were used to implement exact crop rotations and nitrogen fertilization into
the model. Nash-Sutcliffe-Efficiencies for streamflow were 0.54 during the
calibration and 0.57 for the validation period. The modeling performance for
nitrate loadings were lower with 0.31 for the calibration and 0.42 for the
validation period. The average crop yields were reproduced well, while SWAT
failed to reproduce the inter-annual crop yield variations. A scenario
analysis revealed that a slight decrease of nitrogen fertilization leads to
significant reductions in nitrate loadings, while crop yields remained on a
high level. The outcome of the study may help practitioners to operate
according to an economic and environmental optimal N management.
Nevertheless, experimental studies with varying fertilization intensities at
catchment scale are needed to underpin the modeling results.</p
Modelling marine emissions and atmospheric distributions of halocarbons and dimethyl sulfide: the influence of prescribed water concentration vs. prescribed emissions
Marine-produced short-lived trace gases such as dibromomethane (CH2Br2), bromoform (CHBr3), methyliodide (CH3I) and dimethyl sulfide (DMS) significantly impact tropospheric and stratospheric chemistry. Describing their marine emissions in atmospheric chemistry models as accurately as possible is necessary to quantify their impact on ozone depletion and Earth's radiative budget. So far, marine emissions of trace gases have mainly been prescribed from emission climatologies, thus lacking the interaction between the actual state of the atmosphere and the ocean. Here we present simulations with the chemistry climate model EMAC (ECHAM5/MESSy Atmospheric Chemistry) with online calculation of emissions based on surface water concentrations, in contrast to directly prescribed emissions. Considering the actual state of the model atmosphere results in a concentration gradient consistent with model real-time conditions at the ocean surface and in the atmosphere, which determine the direction and magnitude of the computed flux. This method has a number of conceptual and practical benefits, as the modelled emission can respond consistently to changes in sea surface temperature, surface wind speed, sea ice cover and especially atmospheric mixing ratio. This online calculation could enhance, dampen or even invert the fluxes (i.e. deposition instead of emissions) of very short-lived substances (VSLS). We show that differences between prescribing emissions and prescribing concentrations (−28 % for CH2Br2 to +11 % for CHBr3) result mainly from consideration of the actual, time-varying state of the atmosphere. The absolute magnitude of the differences depends mainly on the surface ocean saturation of each particular gas. Comparison to observations from aircraft, ships and ground stations reveals that computing the air–sea flux interactively leads in most of the cases to more accurate atmospheric mixing ratios in the model compared to the computation from prescribed emissions. Calculating emissions online also enables effective testing of different air–sea transfer velocity (k) parameterizations, which was performed here for eight different parameterizations. The testing of these different k values is of special interest for DMS, as recently published parameterizations derived by direct flux measurements using eddy covariance measurements suggest decreasing k values at high wind speeds or a linear relationship with wind speed. Implementing these parameterizations reduces discrepancies in modelled DMS atmospheric mixing ratios and observations by a factor of 1.5 compared to parameterizations with a quadratic or cubic relationship to wind spee
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Enigmatic persistence of dissolved organic matter in the ocean
Marine dissolved organic matter (DOM) contains more carbon than the combined stocks of Earth’s biota. Organisms in the ocean continuously release a myriad of molecules that become food for microheterotrophs, but, for unknown reasons, a residual fraction persists as DOM for millennia. In this Perspective, we discuss and compare two concepts that could explain this persistence. The long-standing ‘intrinsic recalcitrance’ paradigm attributes DOM stability to inherent molecular properties. In the ‘emergent recalcitrance’ concept, DOM is continuously transformed by marine microheterotrophs, with recalcitrance emerging on an ecosystems level. Both concepts are consistent with observations in the modern ocean, but they imply very different responses of the DOM pool to climate-related changes. To better understand DOM persistence, we propose a new overarching research strategy — the ecology of molecules — that integrates the concepts of intrinsic and emergent recalcitrance with the ecological and environmental context
A role for PKC-ɛ in FcγR-mediated phagocytosis by RAW 264.7 cells
Protein kinase C (PKC) plays a prominent role in immune signaling, and the paradigms for isoform selective signaling are beginning to be elucidated. Real-time microscopy was combined with molecular and biochemical approaches to demonstrate a role for PKC-ɛ in Fcγ receptor (FcγR)–dependent phagocytosis. RAW 264.7 macrophages were transfected with GFP-conjugated PKC isoforms, and GFP movement was followed during phagocytosis of fluorescent IgG–opsonized beads. PKC-ɛ, but not PKC-δ, concentrated around the beads. PKC-ɛ accumulation was transient; apparent as a “flash” on target ingestion. Similarly, endogenous PKC-ɛ was specifically recruited to the nascent phagosomes in a time-dependent manner. Overexpression of PKC-ɛ, but not PKC-α, PKC-δ, or PKC-γ enhanced bead uptake 1.8-fold. Additionally, the rate of phagocytosis in GFP PKC-ɛ expressors was twice that of cells expressing GFP PKC-δ. Expression of the regulatory domain (ɛRD) and the first variable region (ɛV1) of PKC-ɛ inhibited uptake, whereas the corresponding PKC-δ region had no effect. Actin polymerization was enhanced on expression of GFP PKC-ɛ and ɛRD, but decreased in cells expressing ɛV1, suggesting that the ɛRD and ɛV1 inhibition of phagocytosis is not due to effects on actin polymerization. These results demonstrate a role for PKC-ɛ in FcγR-mediated phagocytosis that is independent of its effects on actin assembly
Assessing a New Clue to How Much Carbon Plants Take Up
Current climate models disagree on how much carbon dioxide land ecosystems take up for photosynthesis. Tracking the stronger carbonyl sulfide signal could help
Modelling marine emissions and atmospheric distributions of halocarbons and dimethyl sulfide: The influence of prescribed water concentration vs. prescribed emissions
Marine-produced short-lived trace gases such as dibromomethane (CHBr), bromoform (CHBr), methyliodide (CHI) and dimethyl sulfide (DMS) significantly impact tropospheric and stratospheric chemistry. Describing their marine emissions in atmospheric chemistry models as accurately as possible is necessary to quantify their impact on ozone depletion and Earth’s radiative budget. So far, marine emissions of trace gases have mainly been prescribed from emission climatologies, thus lacking the interaction between the actual state of the atmosphere and the ocean. Here we present simulations with the chemistry climate model EMAC (ECHAM5/MESSy Atmospheric Chemistry) with online calculation of emissions based on surface water concentrations, in contrast to directly prescribed emissions. Considering the actual state of the model atmosphere results in a concentration gradient consistent with model realtime conditions at the ocean surface and in the atmosphere, which determine the direction and magnitude of the computed flux. This method has a number of conceptual and practical benefits, as the modelled emission can respond consistently to changes in sea surface temperature, surface wind speed, sea ice cover and especially atmospheric mixing ratio. This online calculation could enhance, dampen or even invert the fluxes (i.e. deposition instead of emissions) of very short-lived substances (VSLS). We show that differences between prescribing emissions and prescribing concentrations (-28%for CHBr to +11%for CHBr) result mainly from consideration of the actual, time-varying state of the atmosphere. The absolute magnitude of the differences depends mainly on the surface ocean saturation of each particular gas. Comparison to observations from aircraft, ships and ground stations reveals that computing the air–sea flux interactively leads in most of the cases to more accurate atmospheric mixing ratios in the model compared to the computation from prescribed emissions. Calculating emissions online also enables effective testing of different air–sea transfer velocity (k) parameterizations, which was performed here for eight different parameterizations. The testing of these different k values is of special interest for DMS, as recently published parameterizations derived by direct flux measurements using eddy covariance measurements suggest decreasing k values at high wind speeds or a linear relationship with wind speed. Implementing these parameterizations reduces discrepancies in modelled DMS atmospheric mixing ratios and observations by a factor of 1.5 compared to parameterizations with a quadratic or cubic relationship to wind speed
Brominated VSLS and their influence on ozone under a changing climate
Very short-lived substances (VSLS) contribute as source gases
significantly to the tropospheric and stratospheric bromine
loading. At present, an estimated 25 % of stratospheric
bromine is of oceanic origin. In this study, we investigate how
climate change may impact the ocean–atmosphere flux of brominated
VSLS, their atmospheric transport, and chemical transformations and
evaluate how these changes will affect stratospheric ozone over the
21st century.
Under the assumption of fixed ocean water concentrations and RCP6.0
scenario, we find an increase of the ocean–atmosphere flux of
brominated VSLS of about 8–10 % by the end of the 21st
century compared to present day. A decrease in the tropospheric
mixing ratios of VSLS and an increase in the lower stratosphere are
attributed to changes in atmospheric chemistry and transport. Our
model simulations reveal that this increase is counteracted by
a corresponding reduction of inorganic bromine. Therefore the total
amount of bromine from VSLS in the stratosphere will not be changed by
an increase in upwelling. Part of the increase of VSLS in the tropical
lower stratosphere results from an increase in the corresponding
tropopause height. As the depletion of stratospheric ozone due to
bromine depends also on the availability of chlorine, we find the
impact of bromine on stratospheric ozone at the end of the 21st
century reduced compared to present day. Thus, these studies
highlight the different factors influencing the role of brominated
VSLS in a future climate
Point-occurrence self-similarity in crackling-noise systems and in other complex systems
It has been recently found that a number of systems displaying crackling
noise also show a remarkable behavior regarding the temporal occurrence of
successive events versus their size: a scaling law for the probability
distributions of waiting times as a function of a minimum size is fulfilled,
signaling the existence on those systems of self-similarity in time-size. This
property is also present in some non-crackling systems. Here, the uncommon
character of the scaling law is illustrated with simple marked renewal
processes, built by definition with no correlations. Whereas processes with a
finite mean waiting time do not fulfill a scaling law in general and tend
towards a Poisson process in the limit of very high sizes, processes without a
finite mean tend to another class of distributions, characterized by double
power-law waiting-time densities. This is somehow reminiscent of the
generalized central limit theorem. A model with short-range correlations is not
able to escape from the attraction of those limit distributions. A discussion
on open problems in the modeling of these properties is provided.Comment: Submitted to J. Stat. Mech. for the proceedings of UPON 2008 (Lyon),
topic: crackling nois
Exploding House Prices in Urban Housing Markets: Explanations and Policy Solutions for the Netherlands
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