Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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The uncertain climate footprint of wetlands under human pressure
Petrescu, A.J. ; Lohila, A. ; Tuovinen, J.P. ; Baldocchi, D.D. ; Desai, A.R. ; Veenendaal, E.M. ; Schrier-Uijl, A. - \ 2015
Proceedings of the National Academy of Sciences of the United States of America 112 (2015)15. - ISSN 0027-8424 - p. 4594 - 4599.
methane emissions - carbon-dioxide - peatlands - ecosystem - fluxes - variability - dynamics - drainage - balance - cycle
Significant climate risks are associated with a positive carbon–temperature feedback in northern latitude carbon-rich ecosystems, making an accurate analysis of human impacts on the net greenhouse gas balance of wetlands a priority. Here, we provide a coherent assessment of the climate footprint of a network of wetland sites based on simultaneous and quasi-continuous ecosystem observations of CO2 and CH4 fluxes. Experimental areas are located both in natural and in managed wetlands and cover a wide range of climatic regions, ecosystem types, and management practices. Based on direct observations we predict that sustained CH4 emissions in natural ecosystems are in the long term (i.e., several centuries) typically offset by CO2 uptake, although with large spatiotemporal variability. Using a space-for-time analogy across ecological and climatic gradients, we represent the chronosequence from natural to managed conditions to quantify the “cost” of CH4 emissions for the benefit of net carbon sequestration. With a sustained pulse–response radiative forcing model, we found a significant increase in atmospheric forcing due to land management, in particular for wetland converted to cropland. Our results quantify the role of human activities on the climate footprint of northern wetlands and call for development of active mitigation strategies for managed wetlands and new guidelines of the Intergovernmental Panel on Climate Change (IPCC) accounting for both sustained CH4 emissions and cumulative CO2 exchange.
Temporal and spatial variability of urban heat island and thermal comfort within the Rotterdam agglomeration
Hove, B. van; Jacobs, C.M.J. ; Heusinkveld, B.G. ; Elbers, J.A. ; Driel, B.L. van; Holtslag, A.A.M. - \ 2015
Building and Environment 83 (2015). - ISSN 0360-1323 - p. 91 - 103.
klimaatverandering - temperatuur - perceptie - stedelijke gebieden - ruimtelijke variatie - variatie in de tijd - rotterdam - climatic change - temperature - perception - urban areas - spatial variation - temporal variation - rotterdam - air-temperature - street geometry - canyon geometry - climate zones - land-use - environment - areas - radiation - impact - fluxes
This paper reports on temporal and spatial variability of local climate and outdoor human thermal comfort within the Rotterdam agglomeration. We analyse three years of meteorological observations (2010–2012) from a monitoring network. Focus is on the atmospheric urban heat island (UHI); the difference in air temperature between urban areas and rural surroundings. In addition, we calculate the Physiologically Equivalent Temperature (PET) which is a measure of thermal comfort. Subsequently, we determine the dependency of intra-urban variability in local climate and PET on urban land-use and geometric characteristics. During a large part of the year, UHI-intensities in densely built areas can be considerable, under calm and clear (cloudless) weather conditions. The highest maximum UHI-values are found in summer, with 95-percentile values ranging from 4.3 K to more than 8 K, depending on the location. In winter, UHI-intensities are generally lower. Intra-urban variability in maximum UHI-intensity is considerable, indicating that local features have an important influence. It is found to be significantly related to building, impervious and green surface fractions, respectively, as well as to mean building height. In summer, urban areas show a larger number of discomfort hours (PET > 23 °C) compared to the reference rural area. Our results indicate that this is mainly related to the much lower wind velocities in urban areas. Also intra-urban variability in thermal comfort during daytime appears to be mainly related to differences in wind velocity. After sunset, the UHI effect plays a more prominent role and hence thermal comfort is more related with urban characteristics.
Nitrous oxide and methane emissions from optimized and alternative cereal cropping systems on the North China Plain: A two-year field study
Gao, B. ; Ju, X.T. ; Su, F. ; Meng, Q.F. ; Oenema, O. ; Christie, P. ; Chen, X.P. ; Zhang, F.S. - \ 2014
Science of the Total Environment 472 (2014). - ISSN 0048-9697 - p. 112 - 124.
greenhouse-gas emissions - n2o emissions - soil - management - maize - fertilizer - fluxes - agriculture - balance - intensity
The impacts of different crop rotation systems with their corresponding management practices on grain yield, greenhouse gas emissions, and fertilizer nitrogen (N) and irrigation water use efficiencies are not well documented. This holds especially for the North China Plain which provides the staple food for hundreds of millions of people and where groundwater resources are polluted with nitrate and depleted through irrigation. Here, we report on fertilizer N and irrigation water use, grain yields, and nitrous oxide (N2O) and methane (CH4) emissions of conventional and optimized winter wheat-summer maize double-cropping systems, and of three alternative cropping systems, namely a winter wheat-summer maize (or soybean)-spring maize system, with three harvests in two years; and a single spring maize system with one crop per year. The results of this two-year study show that the optimized double-cropping system led to a significant increase in grain yields and a significant decrease in fertilizer N use and net greenhouse gas intensity, but the net greenhouse gas N2O emissions plus CH4 uptake and the use of irrigation water did not decrease relative to the conventional system. Compared to the conventional system the net greenhouse gas emissions, net greenhouse gas intensity and use of fertilizer N and irrigation water decreased in the three alternative cropping systems, but at the cost of grain yields except in the winter wheat-summer maize-spring maize system. Net uptake of CH4 by the soil was little affected by cropping system. Average N2O emission factors were only 0.17% for winter wheat and 0.53% for maize. In conclusion, the winter wheat-summer maize-spring maize system has considerable potential to decrease water and N use and decrease N2O emissions while maintaining high grain yields and sustainable use of groundwater.
Temperature and moisture affect methane and nitrous oxide emission from bovine manure patches in tropical conditions
Mazzetto, A.M. ; Barneze, A.S. ; Feigl, B.J. ; Groenigen, J.W. van; Oenema, O. ; Cerri, C.C. - \ 2014
Soil Biology and Biochemistry 76 (2014). - ISSN 0038-0717 - p. 242 - 248.
greenhouse-gas emissions - nitrification inhibitor dicyandiamide - excreta deposition - grazed grassland - grazing animals - soils - urine - n2o - fluxes - cattle
Animal production systems are important sources of greenhouse gases (GHG), especially methane (CH4) and nitrous oxide (N2O). Brazilian beef production is almost exclusively (more than 90%) pasture-based. GHG emissions from faeces deposited in pastures have been extensively studied in temperate climates, but emissions under tropical conditions are unclear. The aim of this study was to examine the effects of tropical temperature and moisture conditions on GHG emission from manure. We hypothesized that periodical rainfall and high temperature on tropical climates would increase the GHG emission from faeces by maintaining an anaerobic environment within the faeces. We measured the emission of CH4 and N2O from cattle faeces in two different field sites in Brazil: São Paulo (subtropical) and Rondônia (tropical), as well as under controlled conditions, simulating summer conditions. Emissions of CH4 from faeces ranged from 117 to 1007 mg C–CH4 m-2 h-1. In the field, summer emissions were 2.9 (São Paulo) and 2.5 (Rondônia) times higher than winter (p <0.05). In controlled conditions, prolonged moisture conditions at high temperature (35 °C) resulted in higher emissions (p <0.05) than the no-rewetted treatment (2831 and 1781 mgCH4 m-2, respectively). Emission factors determined were 0.02 and 0.05 kg CH4 head-1 year-1 (winter and summer São Paulo, respectively) and 0.06 and 0.10 kg CH4 head-1 year-1 (winter and summer Rondônia, respectively), significantly lower than the IPCC default value of 1 kg CH4 head-1 year-1. CH4 emissions from faeces were slightly higher than from others studies in temperate climates. N2O emission from faeces was lower than the control at the Rondônia site during the summer, with net negative fluxes. We conclude that climate is a strong factor controlling GHG emission from faeces. Our study showed that in a continental-size country as Brazil, an average emission factor as proposed by the IPCC is not the best option.
Uptake, translocation and elimination in sediment-rooted macrophytes: A model-supported analysis of whole sediment toxicity test data
Diepens, N.J. ; Arts, G.H.P. ; Focks, A. ; Koelmans, A.A. - \ 2014
Environmental Science and Technology 48 (2014)20. - ISSN 0013-936X - p. 12344 - 12353.
hydrophobic organic-chemicals - polychlorinated-biphenyls - myriophyllum-aquaticum - aromatic-hydrocarbons - translocation - pesticides - plants - fluxes - carbon - bioaccumulation
Understanding bioaccumulation in sediment-rooted macrophytes is crucial for the development of sediment toxicity tests using macrophytes. Here we explore bioaccumulation in sediment-rooted macrophytes by tracking and modelling chemical flows of chlorpyrifos, linuron, and six PCBs in water-sediment-macrophyte systems. Chemical fluxes across the interfaces between pore water, overlying water, shoots, and roots were modelled using a novel multi-compartment model. The modelling yielded the first mass transfer parameter set reported for bioaccumulation by sediment-rooted macrophytes, with satisfactory narrow confidence limits for more than half of the estimated parameters. Exposure via the water column led to rapid uptake by Elodea canadensis and Myriophyllum spicatum shoots, followed by transport to the roots within 1-3 days, after which tissue concentrations gradually declined. Translocation played an important role in the exchange between shoots and roots. Exposure via spiked sediment led to gradual uptake by the roots, but subsequent transport to the shoots and overlying water remained limited for the chemicals studied. These contrasting patterns show that exposure is sensitive to test set up, chemical properties, and species traits. Although field-concentrations in water and sediment will differ from those in the tests, the model parameters can be assumed applicable for modelling exposure to macrophytes in the field.
Similarity Relations for C_T^2 in the Unstable Atmospheric Surface Layer: Dependence on Regression Approach, Observation Height and Stability Range
Braam, M. ; Moene, A.F. ; Beyrich, F. ; Holtslag, A.A.M. - \ 2014
Boundary-Layer Meteorology 153 (2014)1. - ISSN 0006-8314 - p. 63 - 87.
nocturnal boundary-layer - aperture scintillometer - structure parameters - sonic anemometer - sensible heat - fluxes - temperature - scintillation - cases-99 - momentum
A great variety of similarity functions for the structure parameter of temperature ( C 2 T ) have been proposed in the literature. They differ in the way they were derived from the data and in the characteristics of the dataset used for their derivation (surface type, observation level, stability range). In this study, we use one single dataset (CASES-99 experiment) and investigate the impact on the similarity functions of applying various regression approaches, and measuring at different heights and within different stability ranges. We limit ourselves to similarity functions under unstable conditions, and evaluate only the most common shape that describes the relation with two coefficients ( f(z/L)=c 1 (1-c 2 z/L) -2/3 , where z is the height, and L is the Obukhov length and a measure of the stability, and c 1 and c 2 are the regression coefficients). The results show that applying various regression approaches has an impact on the regression coefficients c 1 and c 2 . Thus studies should always specify the regression approach when presenting similarity relations. We suggest use of an orthogonal distance regression method such that uncertainties in -z/L are also taken into account, to apply this to the logarithmic transformation of both dimensionless groups, and to use a weighted dataset such that unreliable data points have a smaller influence on the fit. Dividing the dataset into eight height ( z ) and eight stability ( -1/L classes) classes, we show that the observation height and the stability range has an impact on the coefficients too. This implies that variations in c 1 and c 2 found in the literature may result from variations in the height and stability ranges among the datasets. Furthermore, application of the coefficients on a dataset obtained at a different height or within a different stability range has to be made with care. Finally, the variation in the coefficients between the classes indicates that the Monin–Obukhov similarity function for C 2 T is not sufficiently described by the two-coefficient function used here.
Limited Reversibility of Bioconcentration of Hydrophobic Organic Chemicals in Phytoplankton
Koelmans, A.A. - \ 2014
Environmental Science and Technology 48 (2014)13. - ISSN 0013-936X - p. 7341 - 7348.
granular activated carbon - selenastrum-capricornutum - polychlorinated biphenyl - kinetics - sediment - water - chlorobenzenes - desorption - sorption - fluxes
Aging, reversibility and desorption rates for the binding of hydrophobic chemicals (HOC) to phytoplankton cells have not been directly measured. Here the effect of bioconcentration time on subsequent desorption of hexachlorobenzene (HCB) and polychlorinated biphenyls (PCBs) was studied for the alga Monoraphidium minutum. Cell suspensions were exposed to HCB and PCBs spanning a range of logKow values of 5.7 to 8.2, for 0.13 to 14 d. Subsequently, reversibility and desorption rates were assessed by extracting the chemicals from the cells using infinite sink extractions with Tenax beads or Empore disks employed in the cell suspension. Uptake was biphasic with constant relative contributions of fast surface sorption. Desorption was biphasic too and fitted well to a first order two compartment model. Increasing exposure times resulted in increasing slowly desorbing chemical fractions and decreased desorption rates from these fractions. For the most hydrophobic PCBs, slowly desorbing fractions were >80-90%, whereas desorption half-lives from these fractions ranged up to 120 days. The slow desorption rates directly prove that bioconcentration to algae can be rate limited and imply that already after a few hours of exposure HOCs may become practically unavailable for repartitioning.
Detection of Entrainment Influences on Surface-Layer Measurements and Extension of Monin–Obukhov Similarity Theory
Boer, A. van de; Moene, A.F. ; Graf, A. ; Schüttemeyer, D. ; Simmer, C. - \ 2014
Boundary-Layer Meteorology 152 (2014)1. - ISSN 0006-8314 - p. 19 - 44.
convective boundary-layer - temperature-humidity correlation - sonic anemometer - analytical-model - mixed-layer - turbulence - fluxes - transport - water - heat
We present a method to detect influences of boundary-layer processes on surface-layer measurements, using statistics and spectra of surface-layer variables only. We validated our detection method with boundary-layer measurements. Furthermore, we confirm that Monin–Obukhov similarity functions fit well to temperature-variance data obtained at two different homogeneous surfaces. However, we found that humidity variance measurements deviate from the universal functions above one of the two studied surfaces for days on which entrained air reached the surface layer. These results confirm that Monin–Obukhov similarity theory should be used with care in the analysis of surface-layer data. Finally, we propose the use of an extra term in flux-variance relations that depends on the entrainment ratio for humidity and on the boundary-layer height. If boundary-layer measurements are not available, we show how the entrainment ratio for humidity can be approximated from the skewness of the humidity distribution
Shallow cumulus rooted in photosynthesis
Vilà-Guerau De Arellano, J. ; Ouwersloot, H.G. ; Baldocchi, D. ; Jacobs, C.M.J. - \ 2014
Geophysical Research Letters 41 (2014)5. - ISSN 0094-8276 - p. 1796 - 1802.
heterogeneous land surfaces - boundary-layer - soil-moisture - gas-exchange - water - formulation - vegetation - clouds - fluxes - co2
We study the interactions between plant evapotranspiration, controlled by photosynthesis (C3 and C4 grasses), and moist thermals responsible for the formation of shallow cumulus clouds (SCu). Our findings are based on a series of systematic numerical experiments at fine spatial and temporal scales using large eddy simulations explicitly coupled to a plant-physiology model. The shading provided by SCu leads to strong spatial variability in photosynthesis and the surface energy balance. This in turn results in SCu characterized by less extreme and less skewed values of liquid water path. The larger water use efficiency of C4 grass leads to two opposite effects that influence boundary layer clouds: more vigorous and deeper thermals due to the larger buoyancy surface flux (positive effect) characterized by less moisture content (negative). We find that under these midlatitude and well-watered soil conditions, SCu are characterized by a larger cloud cover and liquid water path over C4 grass fields.
Variability of the Structure Parameters of Temperature and Humidity Observed in the Atmospheric Surface Layer Under Unstable Conditions
Braam, M. ; Moene, A.F. ; Beyrich, F. - \ 2014
Boundary-Layer Meteorology 150 (2014)3. - ISSN 0006-8314 - p. 399 - 422.
sonic anemometer - water-vapor - aperture scintillometer - heterogeneous surface - local-structure - boundary-layer - sensible heat - fluxes - turbulence - momentum
The structure parameters of temperature and humidity are important in scintillometry as they determine the structure parameter of the refractive index of air, the primary atmospheric variable obtained with scintillometers. In this study, we investigate the variability of the logarithm of the Monin-Obukhov-scaled structure parameters (denoted as log(2s )) of temperature and humidity. We use observations from eddy-covariance systems operated at three heights (2.5, 50, and 90 m) within the atmospheric surface layer under unstable conditions. The variability of log(C2 s ) depends on instability and on the size of the averaging window over which log(C2 s ) is calculated. If instability increases, differences in log(C2s ) between upward motions (large C2 s ) and downward motions (small C2 s ) increase. The differences are, however, not sufficiently large to result in a bimodal probability density function. If the averaging window size increases, the variances of log(C2 s ) decrease. A linear regression of the variances of log(C2 s ) versus the averaging window size for various stability classes shows an increase of both the offset and slope (in absolute sense) with increasing instability. For temperature, data from the three heights show comparable results. For humidity, in contrast, the offset and slope are larger at 50 and 90 m than at 2.5 m. In the end we discuss how these findings could be used to assess whether observed differences in C2 s along a scintillometer path or aircraft flight leg are just within the range of local variability in C2 s or could be attributed to surface heterogeneity. This is important for the interpretation of data measured above a heterogeneous surface.
Global water resources affected by human interventionss and climate change
Haddeland, I. ; Heinke, J. ; Biemans, H. ; Eisner, S. ; Florke, M.F. ; Hanasaki, N. ; Konzmann, M. ; Ludwig, F. - \ 2014
Proceedings of the National Academy of Sciences of the United States of America 111 (2014)9. - ISSN 0027-8424 - p. 3251 - 3256.
integrated model - bias correction - surface-water - validation - fluxes - scheme
Humans directly change the dynamics of the water cycle through dams constructed for water storage, and through water withdrawals for industrial, agricultural, or domestic purposes. Climate change is expected to additionally affect water supply and demand. Here, analyses of climate change and direct human impacts on the terrestrial water cycle are presented and compared using a multimodel approach. Seven global hydrological models have been forced with multiple climate projections, and with and without taking into account impacts of human interventions such as dams and water withdrawals on the hydrological cycle. Model results are analyzed for different levels of global warming, allowing for analyses in line with temperature targets for climate change mitigation. The results indicate that direct human impacts on the water cycle in some regions, e.g., parts of Asia and in the western United States, are of the same order of magnitude, or even exceed impacts to be expected for moderate levels of global warming (+2 K). Despite some spread in model projections, irrigation water consumption is generally projected to increase with higher global mean temperatures. Irrigation water scarcity is particularly large in parts of southern and eastern Asia, and is expected to become even larger in the future.
Canal blocking strategies for hydrological restoration of degraded tropical peatlands in Central Kalimantan, Indonesia
Ritzema, H.P. ; Limin, S. ; Kusin, K. ; Jauhiainen, J. ; Wösten, H. - \ 2014
Catena 114 (2014). - ISSN 0341-8162 - p. 11 - 20.
peat swamp forest - carbon-dioxide - southeast-asia - fluxes - land - co2 - fires - n2o - ch4
In the 1990s the Government of Indonesia derided to develop one million hectares of peatlands for agriculture in Central Kalimantan on the Island of Borneo. The construction of thousands of kilometres of canals resulted in over-drainage and targets for agricultural production failed. Abandoned, the area has been subject to severe forest and peat fires. Restoration of degraded peatlands normally starts with restoring the water table to rewet the surface in order to control fire and to initiate reforestation. Canal blocking strategies are a potential means for accomplishing this. In a test plot in the Northern part of Block C of the former Mega Rice Project (MRP), a series of dams were constructed and (ground)water tables and subsidence rates were monitored to assess the effects of dam construction on peatland hydrology. The resulting higher water tables did not completely compensate for the negative effects of increased subsidence near the canals. The canals, which are "eating" themselves into the peatland, create depressions in the peatland surface leading to interception of overland- and interflow and increased risk of overtopping of dams during extreme rainfall events. The lessons learned are being used to improve blocking strategies and dam design. The changes in peatland topography caused by drainage, however, need to be better understood in order to further refine strategies for hydrological restoration of degraded peatlands in Indonesia. (C) 2013 Elsevier B.V. All rights reserved.
On the variation of regional CO2 exchange over temperate and boreal North America
Zhang, X. ; Gurney, K.R. ; Peylin, P. ; Chevallier, F. ; Law, R.M. ; Patra, P.K. ; Rayner, P.J. ; Roedenbeck, C. ; Krol, M.C. - \ 2013
Global Biogeochemical Cycles 27 (2013)4. - ISSN 0886-6236 - p. 991 - 1000.
atmospheric carbon-dioxide - terrestrial ecosystems - united-states - interannual variability - climate - forest - trends - drought - fluxes - land
Inverse-estimated net carbon exchange time series spanning two decades for six North American regions are analyzed to examine long-term trends and relationships to temperature and precipitation variations. Results reveal intensification of carbon uptake in eastern boreal North America (0.1 PgC/decade) and the Midwest United States (0.08 PgC/decade). Seasonal cross-correlation analysis shows a significant relationship between net carbon exchange and temperature/precipitation anomalies during the western United States growing season with warmer, dryer conditions leading reduced carbon uptake. This relationship is consistent with global change-type drought dynamics which drive increased vegetation mortality, increases in dry woody material, and increased wildfire occurrence. This finding supports the contention that future climate change may increase carbon loss in this region. Similarly, higher temperatures and reduced precipitation are accompanied by decreased net carbon uptake in the Midwestern United States toward the end of the growing season. Additionally, intensified net carbon uptake during the eastern boreal North America growing season is led by increased precipitation anomalies in the previous year, suggesting the influence of climate memory carried by regional snowmelt water. The two regions of boreal North America exhibit opposing seasonal carbon-temperature relationships with the eastern half experiencing a net carbon loss with near coincident increases in temperature and the western half showing increased net carbon uptake. The carbon response in the boreal west region lags the temperature anomalies by roughly 6months. This opposing carbon-temperature relationship in boreal North America may be a combination of different dominant vegetation types, the amount and timing of snowfall, and temperature anomaly differences across boreal North America.
N2O consumption by low-nitrogen soil and its regulation by water and oxygen
Wu, D.M. ; Dong, W.X. ; Oenema, O. ; Wang, Y.Y. ; Trebs, I. ; Hu, C.S. - \ 2013
Soil Biology and Biochemistry 60 (2013). - ISSN 0038-0717 - p. 165 - 172.
spruce forest soil - aerobic denitrification - oxide - fluxes - emissions - exchange - n-2 - no - bacteria - nitrate
Soils can be a source and sink for atmospheric nitrous oxide (N2O). Consumption of N2O has been reported for anoxic soils and sediments rich in organic matter and depleted in nitrates (NO3-), and also for some dry, oxic soils. However, the mechanisms and controls of N2O consumption in dry soil are not clear. Here, we report on a field study in China (Taihang mountain region, Shijiazhuang), in which N2O uptake by a sandy loam soil was measured for the greater part of the season (from April to October in 2011), and on four incubation experiments, in which we tried to reveal the roles of water content and oxygen (O-2) concentrations on N2O consumption. Flux measurements in the field were made bi-weekly on unfertilized cropped land with static flux chambers (5 replicates) for 6 months. The results show that N2O-N fluxes ranged from -26.0 to -726.6 mu g m(-2) h(-1). Consumption of N2O was largest when the soil was dry (5-20% soil water filled pore space). In the incubation experiments, N2O consumption and N-2 production were measured in (an)aerobic soil with soil moisture content ranging from 1% to 50% (wt/wt) and with N2O addition, using a thermostatic, robotized incubation system. Under anaerobic conditions, N2O was rapidly consumed at water content of >10% (wt/wt). However, a significant consumption also occurred at 1% soil moisture. Under aerobic conditions, N2O consumption increased with increasing soil moisture content, but significant consumption was still measured at 2% moisture. Sterilization of oxic soil completely blocked N2O consumption, suggesting that the consumption had a biological nature. In conclusion, the steady N2O consumption measured in the field was confirmed by the laboratory experiments, but the relationship with soil moisture content was reversed. Further studies are required to understand this apparent anomaly.
Role of maize stover incorporation on nitrogen oxide emissions in a non-irrigated Mediterranean barley field
Abalos, D. ; Sanz-Cobena, A. ; Garcia-Torres, L. ; Groenigen, J.W. van; Vallejo, A. - \ 2013
Plant and Soil 364 (2013)1-2. - ISSN 0032-079X - p. 357 - 371.
treated pig slurries - nitric-oxide - inorganic fertilizer - microbial biomass - plant residues - crop residues - soil - n2o - fluxes - denitrification
Agricultural soils in semiarid Mediterranean areas are characterized by low organic matter contents and low fertility levels. Application of crop residues and/or manures as amendments is a cost-effective and sustainable alternative to overcome this problem. However, these management practices may induce important changes in the nitrogen oxide emissions from these agroecosystems, with additional impacts on carbon dioxide emissions. In this context, a field experiment was carried out with a barley (Hordeum vulgare L.) crop under Mediterranean conditions to evaluate the effect of combining maize (Zea mays L.) residues and N fertilizer inputs (organic and/or mineral) on these emissions. Crop yield and N uptake, soil mineral N concentrations, dissolved organic carbon (DOC), denitrification capacity, N2O, NO and CO2 fluxes were measured during the growing season. The incorporation of maize stover increased N2O emissions during the experimental period by c. 105 %. Conversely, NO emissions were significantly reduced in the plots amended with crop residues. The partial substitution of urea by pig slurry reduced net N2O emissions by 46 and 39 %, with and without the incorporation of crop residues respectively. Net emissions of NO were reduced 38 and 17 % for the same treatments. Molar DOC:NO (3) (-) ratio was found to be a robust predictor of N2O and NO fluxes. The main effect of the interaction between crop residue and N fertilizer application occurred in the medium term (4-6 month after application), enhancing N2O emissions and decreasing NO emissions as consequence of residue incorporation. The substitution of urea by pig slurry can be considered a good management strategy since N2O and NO emissions were reduced by the use of the organic residue.
Quantifying the transport of subcloud layer reactants by shallow cimulus clouds over the Amazon
Ouwersloot, H.G. ; Vilà-Guerau De Arellano, J. ; Stratum, B.J.H. van; Krol, M.C. ; Lelieveld, J. - \ 2013
Journal of Geophysical Research: Atmospheres 118 (2013)23. - ISSN 2169-897X - p. 13041 - 13059.
large-eddy simulation - topped mixed layers - convective boundary-layer - diurnal cycle - surface - land - fluxes - model - chemistry - campaign
We investigate the vertical transport of atmospheric chemical reactants from the subcloud layer to the cumulus cloud layer driven by shallow convection over the Amazon during the dry season. The dynamical and chemical assumptions needed for mesoscale and global chemistry transport model parametrizations are systematically analyzed using a Large Eddy Simulation model. We quantify the mass flux transport contribution to the temporal evolution of reactants. Isoprene, a key atmospheric compound over the tropical rain forest, decreases by 8.5% h-1 on average and 15% h-1 at maximum due to mass¿flux¿induced removal. We apply mass flux parametrizations for the transport of chemical reactants and obtain satisfactory agreement with numerically resolved transport, except for some reactants like O3, NO, and NO2. The latter is caused by the local partitioning of reactants, influenced by UV radiation extinction by clouds and small¿scale variability of ambient atmospheric compounds. By considering the longer¿lived NOx (NO + NO2), the transport is well represented by the parametrization. Finally, by considering heterogeneous surface exchange conditions, it is demonstrated that the parametrizations are sensitive to boundary conditions due to changes in the boundary layer dynamics.
Quantified turbulent diffusion of suspended sediment using acoustic Doppler current profilers
Sassi, M.G. ; Hoitink, A.J.F. ; Vermeulen, B. - \ 2013
Geophysical Research Letters 40 (2013)21. - ISSN 0094-8276 - p. 5692 - 5697.
reynolds stress - boundary-layer - open channels - flow - suspension - transport - fluxes - adcp - sand
Collocated profiles of the Reynolds stress tensor and eddy covariance fluxes are obtained to derive vertical profiles of turbulent momentum and sediment diffusivity in a tidal river, using coupled acoustic Doppler current profilers (ADCPs). Shear and normal stresses are obtained by combining the variances in radial velocities measured by the ADCP beams. The covariances between radial velocities and calibrated acoustic backscatter allow the determination of the three Cartesian components of the turbulent flux of suspended sediment. The main advantage of this new approach is that flow velocity and sediment concentration measurements are exactly collocated, and allowing for profiling over longer ranges, in comparison to existing techniques. Results show that vertical profiles of the inverse turbulent Prandtl-Schmidt number are coherent with corresponding profiles of the sediment diffusivity, rather than with profiles of the eddy viscosity.
Global atmospheric carbon budget: results from an ensemble of atmospheric CO2 inversions.
Peylin, P. ; Law, R.M. ; Gurney, K.R. ; Chevallier, F. ; Jacobsen, A.R. ; Maki, T. ; Niwa, Y. ; Patra, P.K. ; Peters, W. ; Rayner, P.J. ; Rödenbeck, C. ; Laan-Luijkx, I.T. van der; Zhang, X. - \ 2013
Biogeosciences 10 (2013). - ISSN 1726-4170 - p. 6699 - 6720.
interannual variability - dioxide exchange - transport model - sinks - fluxes - sensitivity - ocean - land - cycle - emissions
Atmospheric CO2 inversions estimate surface carbon fluxes from an optimal fit to atmospheric CO2 measurements, usually including prior constraints on the flux estimates. Eleven sets of carbon flux estimates are compared, generated by different inversions systems that vary in their inversions methods, choice of atmospheric data, transport model and prior information. The inversions were run for at least 5 yr in the period between 1990 and 2010. Mean fluxes for 2001-2004, seasonal cycles, interannual variability and trends are compared for the tropics and northern and southern extra-tropics, and separately for land and ocean. Some continental/basin-scale subdivisions are also considered where the atmospheric network is denser. Four-year mean fluxes are reasonably consistent across inversions at global/latitudinal scale, with a large total (land plus ocean) carbon uptake in the north (-3.4 Pg C yr(-1) (+/- 0.5 Pg C yr(-1) standard deviation), with slightly more uptake over land than over ocean), a significant although more variable source over the tropics (1.6 +/- 0.9 Pg C yr(-1)) and a compensatory sink of similar magnitude in the south (-1.4 +/- 0.5 Pg C yr(-1)) corresponding mainly to an ocean sink. Largest differences across inversions occur in the balance between tropical land sources and southern land sinks. Interannual variability (IAV) in carbon fluxes is larger for land than ocean regions (standard deviation around 1.06 versus 0.33 Pg C yr(-1) for the 1996-2007 period), with much higher consistency among the inversions for the land. While the tropical land explains most of the IAV (standard deviation similar to 0.65 Pg C yr(-1)), the northern and southern land also contribute (standard deviation similar to 0.39 Pg C yr(-1)). Most inversions tend to indicate an increase of the northern land carbon uptake from late 1990s to 2008 (around 0.1 Pg C yr(-1)), predominantly in North Asia. The mean seasonal cycle appears to be well constrained by the atmospheric data over the northern land (at the continental scale), but still highly dependent on the prior flux seasonality over the ocean. Finally we provide recommendations to interpret the regional fluxes, along with the uncertainty estimates.
Earthworms can increase nitrous oxide emissions from managed grassland: a field study
Lubbers, I.M. ; López González, E. ; Hummelink, E.W.J. ; Groenigen, J.W. van - \ 2013
Agriculture, Ecosystems and Environment 174 (2013). - ISSN 0167-8809 - p. 40 - 48.
nitrifier denitrification - carbon-dioxide - n2o emission - crop residue - soil - fluxes - agroecosystem - mesocosms - peat - gut
Earthworms are important in determining the greenhouse gas (GHG) balance of soils. In laboratory studies they have been shown to increase emissions of the potent GHG nitrous oxide (N2O). Here we test whether these earthworm-induced N2O emissions also occur in the field. We quantified N2O emissions in managed grassland in two different seasons (spring and autumn), applying two different types of fertilizer (organic and artificial fertilizer) and under two earthworm densities (175 individuals and 350 individuals m(-2)) of the species Lumbricus rubellus (Hoffmeister). We found an increase in earthworm-induced N2O emissions of 286 and 394% in autumn for low and high earthworm densities (P = 0.044 and P = 0.007, respectively). There were no effects of earthworms on N2O emissions in spring. Fertilizer additions significantly increased cumulative N2O emissions and grass N content in spring and autumn. For grass N content interactions between earthworm addition and fertilizer type existed in both seasons. Our results suggest that the pathways through which earthworms affect N cycling (and thereby N2O emission) differ with weather conditions. We postulate that in spring the dry weather conditions overruled any earthworm effects, whereas in autumn earthworms mainly improved soil aeration and thereby increased both plant N uptake and diffusion of N2O to the atmosphere. While we showed the presence of earthworm-induced N2O emissions in managed grassland under field conditions for the first time, the nature and intensity of the earthworm effect in the field is conditional on soil physicochemical parameters and thereby on meteorological and seasonal dynamics. (C) 2013 Elsevier B.V. All rights reserved.
Stable atmospheric boundary layers and diurnal Cycles-Challenges for Weather and Climate Models
Holtslag, A.A.M. ; Svensson, G. ; Baas, P. ; Basu, S. ; Beare, B. ; Beljaars, A.C.M. ; Bosveld, F.C. ; Cuxart, J. ; Lindvall, J. ; Steeneveld, G.J. ; Tjernstrom, M. ; Wiel, B.J.H. van de - \ 2013
Bulletin of the American Meteorological Society 94 (2013). - ISSN 0003-0007 - p. 1691 - 1706.
low-level jets - land-surface - contrasting nights - soil-moisture - ecmwf model - sea-ice - turbulence - cases-99 - parameterization - fluxes
The representation of the atmospheric boundary layer is an important part of weather and climate models and impacts many applications such as air quality and wind energy. Over the years, the performance in modeling 2 m temperature and 10 m wind speed has improved but errors are still significant. This is in particular the case under clear skies and low wind-speed conditions at night as well as during winter in stably stratified conditions over land and ice. In this paper, we review these issues and provide an overview of the current understanding and model performance. Results from weather forecast and climate models are used to illustrate the state of the art, as well as findings and recommendations from three inter-comparison studies held within the “Global Energy and Water Exchanges (GEWEX)” Atmospheric Boundary Layer Study (GABLS). Within GABLS, the focus has been on the examination of the representation of the stable boundary layer and the diurnal cycle over land in clear sky conditions. For this purpose, single-column versions of weather and climate models have been compared with observations, research models and Large Eddy Simulations. The intercomparison cases are based on observations taken in the Arctic, Kansas and at Cabauw in the Netherlands. From these studies, we find that even for the non-cloudy boundary layer important parameterization challenges remain.
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