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.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Bodemonderzoek Lieftinghsbroek : ecopedologisch en bedemchemisch onderzoek voor maatregelen tegen effecten van stikstofdepositie
    Waal, R.W. de; Delft, S.P.J. van - \ 2014
    Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2580) - 59
    natura 2000 - bodemchemie - stikstofgehalte - droge depositie - graslanden - beekdalen - groningen - natura 2000 - soil chemistry - nitrogen content - dry deposition - grasslands - brook valleys - groningen
    Oerview of critical loads for nitrogen deposition of Natura 2000 habitat types occurring in The Netherlands
    Dobben, H.F. van; Bobbink, R. ; Bal, D. ; Hinsberg, A. van - \ 2014
    Wageningen : Alterra, Wageningen-UR (Alterra-report 2488) - 61
    natura 2000 - habitats - droge depositie - stikstof - emissiereductie - critical loads - natura 2000 - habitats - dry deposition - nitrogen - emission reduction - critical loads
    In this report an overview of unique critical load values for nitrogen deposition is presented for the Natura 2000-habitat types that occur in The Netherlands, and additionally for the nitrogen sensitive other habitats of species that are protected in Natura 2000-sites. These values are derived by combining the critical load ranges determined by UN-ECE in 2010, and specific model results for The Netherlands. If no other sources were available, expert opinion has been used. The results are in the form of unique (single) values that are always within the UN-ECE ranges.
    Dynamics of nitrogen oxides and ozone above and within a mixed hardwood forest in Northern Michigan
    Seok, B. ; Helmig, D. ; Ganzeveld, L.N. ; Williams, W. ; vogel, C.S. - \ 2013
    Atmospheric Chemistry and Physics 13 (2013). - ISSN 1680-7316 - p. 7301 - 7320.
    reactive oxidized nitrogen - volatile organic-compounds - nitric-acid photolysis - biogenic nox emissions - gas-phase chemistry - dry deposition - atmospheric chemistry - tropospheric ozone - global-model - canopy
    The dynamic behavior of nitrogen oxides (NOx=NO+NO2) and ozone (O3) above and within the canopy at the University of Michigan Biological Station AmeriFlux (UMBS Flux) site was investigated by continuous multi-height vertical gradient measurements during the summer and the fall of 2008. A daily maximum in nitric oxide (NO) mixing ratios was consistently observed during the morning hours between 06:00 and 09:00 EST above the canopy. Daily NO maxima ranged between 0.1 and 2 ppbv (with a median of 0.3 ppbv), which were 2 to 20 times above the atmospheric background. The sources and causes of the morning NO maximum were evaluated using NOx and O3 measurements and synoptic and micrometeorological data. Numerical simulations with a multi-layer canopy-exchange model were done to further support this analysis. The observations indicated that the morning NO maximum was caused by the photolysis of NO2 from non-local air masses, which were transported into the canopy from aloft during the morning breakup of the nocturnal boundary layer. The analysis of simulated process tendencies indicated that the downward turbulent transport of NOx into the canopy compensates for the removal of NOx through chemistry and dry deposition. The sensitivity of NOx and O3 concentrations to soil and foliage NOx emissions was also assessed with the model. Uncertainties associated with the emissions of NOx from the soil or from leaf-surface nitrate photolysis did not explain the observed diurnal behavior in NOx (and O3) and, in particular, the morning peak in NOx mixing ratios. However, a 30% increase in early morning NOx and NO peak mixing ratios was simulated when a foliage exchange NO2 compensation point was considered. This increase suggests the potential importance of leaf-level, bidirectional exchange of NO2 in understanding the observed temporal variability in NOx at UMBS.
    Atmosphere-ocean ozone fluxes during the TexAQS 2006, STRATUS 2006, GOMECC 2007, GasEx 2008, and AMMA 2008 cruises
    Helmig, D. ; Lang, E.K. ; Bariteau, L. ; Boylan, P. ; Fairall, C.W. ; Ganzeveld, L.N. ; Hare, J.E. ; Hueber, J. ; Pallandt, M. - \ 2012
    Journal of Geophysical Research: Atmospheres 117 (2012). - ISSN 2169-897X - 15 p.
    marine boundary-layer - dry deposition - surface - atlantic - iodine - water - coastal - parameterization - enhancement - chemistry
    A ship-based eddy covariance ozone flux system was deployed to investigate the magnitude and variability of ozone surface fluxes over the open ocean. The flux experiments were conducted on five cruises on board the NOAA research vessel Ronald Brown during 2006-2008. The cruises covered the Gulf of Mexico, the southern as well as northern Atlantic, the Southern Ocean, and the persistent stratus cloud region off Chile in the eastern Pacific Ocean. These experiments resulted in the first ship-borne open-ocean ozone flux measurement records. The median of 10 min oceanic ozone deposition velocity (v(d)) results from a combined similar to 1700 h of observations ranged from 0.009 to 0.034 cm s(-1). For the Gulf of Mexico cruise (Texas Air Quality Study (TexAQS)) the median v(d) (interquartile range) was 0.034 (0.009-0.065) cm s(-1) (total number of 10 min measurement intervals, N-f = 1953). For the STRATUS cruise off the Chilean coast, the median v(d) was 0.009 (0.004-0.037) cm s(-1) (N-f = 1336). For the cruise from the Gulf of Mexico and up the eastern U. S. coast (Gulf of Mexico and East Coast Carbon cruise (GOMECC)) a combined value of 0.018 (0.006-0.045) cm s(-1) (N-f = 1784) was obtained (from 0.019 (-0.014-0.043) cm s(-1), N-f = 663 in the Gulf of Mexico, and 0.018 (-0.004-0.045) cm s(-1), N-f = 1121 in the North Atlantic region). The Southern Ocean Gas Exchange Experiment (GasEx) and African Monsoon Multidisciplinary Analysis (AMMA), the Southern Ocean and northeastern Atlantic cruises, respectively, resulted in median ozone v(d) of 0.009 (-0.005-0.026) cm s(-1) (N-f = 2745) and 0.020 (-0.003-0.044) cms(-1) (N-f = 1147). These directly measured ozone deposition values are at the lower end of previously reported data in the literature (0.01-0.12 cm s(-1)) for ocean water. Data illustrate a positive correlation (increase) of the oceanic ozone uptake rate with wind speed, albeit the behavior of the relationship appears to differ during these cruises. The encountered wide range of meteorological and ocean biogeochemical conditions is used to investigate fundamental drivers of oceanic O-3 deposition and for the evaluation of a recently developed global oceanic O-3 deposition modeling system.
    Sources, distribution, and acidity of sulfate–ammonium aerosol in the Arctic in winter–spring
    Fisher, J.A. ; Jacob, D.J. ; Wang, Q. ; Bahreini, R. ; Carouge, C.C. ; Cubison, M.J. ; Dibb, J.E. ; Diehl, T. ; Jiminez, J.L. ; Leibensperger, E.M. ; Lu, Z. ; Meinders, M.B.J. ; Pye, H.O.T. ; Quinn, P.K. ; Sharma, S. ; Streets, D.G. ; Donkelaar, A. van; Yantosca, R.M. - \ 2011
    Atmospheric Environment 45 (2011)39. - ISSN 1352-2310 - p. 7301 - 7318.
    circulation model assessment - cloud resolving simulations - dry deposition - chemical-composition - asian pollution - ice nucleation - air-pollution - intex-b - atmospheric transport - ozone depletion
    We use GEOS-Chem chemical transport model simulations of sulfate–ammonium aerosol data from the NASA ARCTAS and NOAA ARCPAC aircraft campaigns in the North American Arctic in April 2008, together with longer-term data from surface sites, to better understand aerosol sources in the Arctic in winter–spring and the implications for aerosol acidity. Arctic pollution is dominated by transport from mid-latitudes, and we test the relevant ammonia and sulfur dioxide emission inventories in the model by comparison with wet deposition flux data over the source continents. We find that a complicated mix of natural and anthropogenic sources with different vertical signatures is responsible for sulfate concentrations in the Arctic. East Asian pollution influence is weak in winter but becomes important in spring through transport in the free troposphere. European influence is important at all altitudes but never dominant. West Asia (non-Arctic Russia and Kazakhstan) is the largest contributor to Arctic sulfate in surface air in winter, reflecting a southward extension of the Arctic front over that region. Ammonium in Arctic spring mostly originates from anthropogenic sources in East Asia and Europe, with added contribution from boreal fires, resulting in a more neutralized aerosol in the free troposphere than at the surface. The ARCTAS and ARCPAC data indicate a median aerosol neutralization fraction [NH4+]/(2[SO42-] + [NO3-]) of 0.5 mol mol-1 below 2 km and 0.7 mol mol-1 above. We find that East Asian and European aerosol transported to the Arctic is mostly neutralized, whereas West Asian and North American aerosol is highly acidic. Growth of sulfur emissions in West Asia may be responsible for the observed increase in aerosol acidity at Barrow over the past decade. As global sulfur emissions decline over the next decades, increasing aerosol neutralization in the Arctic is expected, potentially accelerating Arctic warming through indirect radiative forcing and feedbacks.
    The impact of Future Land Use and Land Cover Changes on Atmospheric Chemistry-Climate Interactions
    Ganzeveld, L.N. ; Bouwman, L. - \ 2010
    Journal of Geophysical Research: Atmospheres 115 (2010)D23. - ISSN 2169-897X - 18 p.
    general-circulation model - organic-compound emissions - isoprene emissions - technical note - dry deposition - sres scenarios - ozone - surface - echam5/messy1 - exchanges
    To demonstrate potential future consequences of land cover and land use changes beyond those for physical climate and the carbon cycle, we present an analysis of large-scale impacts of land cover and land use changes on atmospheric chemistry using the chemistry-climate model EMAC (ECHAM5/MESSy Atmospheric Chemistry) constrained with present-day and 2050 land cover, land use, and anthropogenic emissions scenarios. Future land use and land cover changes are expected to result in an increase in global annual soil NO emissions by ~1.2 TgN yr-1 (9%), whereas isoprene emissions decrease by ~50 TgC yr-1 (-12%). The analysis shows increases in simulated boundary layer ozone mixing ratios up to ~9 ppbv and more than a doubling in hydroxyl radical concentrations over deforested areas in Africa. Small changes in global atmosphere-biosphere fluxes of NOx and ozone point to compensating effects. Decreases in soil NO emissions in deforested regions are counteracted by a larger canopy release of NOx caused by reduced foliage uptake. Despite this decrease in foliage uptake, the ozone deposition flux does not decrease since surface layer mixing ratios increase because of a reduced oxidation of isoprene by ozone. Our study indicates that the simulated impact of land cover and land use changes on atmospheric chemistry depends on a consistent representation of emissions, deposition, and canopy interactions and their dependence on meteorological, hydrological, and biological drivers to account for these compensating effects. It results in negligible changes in the atmospheric oxidizing capacity and, consequently, in the lifetime of methane. Conversely, we expect a pronounced increase in oxidizing capacity as a consequence of anthropogenic emission increases
    Modeling the surface-atmosphere exchange of ammonia
    Wichink Kruit, R.J. ; Pul, W.A.J. van; Slauter, F.J. ; Broek, M. van den; Nemitz, E. ; Sutton, M.A. ; Krol, M.C. ; Holtslag, A.A.M. - \ 2010
    Atmospheric Environment 44 (2010)7. - ISSN 1352-2310 - p. 945 - 957.
    intensively managed grassland - nh3 deposition processes - oilseed rape plants - compensation point - dry deposition - seminatural vegetation - agricultural grassland - gradient measurements - apoplastic nh4+ - lolium-perenne
    New parameterizations for surfaceeatmosphere exchange of ammonia are presented for application in atmospheric transport models and compared with parameterizations of the literature. The new parameterizations are based on a combination of the results of three years of ammonia flux measurements over a grassland canopy (dominated by Lolium perenne and Poa trivialis) near Wageningen, the Netherlands and existing parameterizations from literature. First, a model for the surfaceeatmosphere exchange of ammonia that includes the concentration at the external leaf surface is derived and validated. Second, a parameterization for the stomatal compensation point (expressed as Gs, the ratio of [NH4+]/[H+] in the leaf apoplast) that accounts for the observed seasonal variation is derived from the measurements. The new, temperature-dependent Gs describes the observed seasonal behavior very well. It is noted, however, that senescence of plants and field management practices will also influence the seasonal variation of Gs on a shorter timescale. Finally, a relation that links Gs to the atmospheric pollution level of the location through the ‘long-term’ NH3 concentration in the air is proposed.
    Global reactive nitrogen deposition from lightning NOx
    Shepon, A. ; Gildor, H. ; Labrador, L.J. ; Butler, T. ; Ganzeveld, L.N. ; Lawrence, M.G. - \ 2007
    Journal of Geophysical Research: Atmospheres 112 (2007). - ISSN 2169-897X - 14 p.
    general-circulation model - dry deposition - atmospheric chemistry - organic nitrogen - climate-change - trace gases - distributions - parameterization - cycle - emissions
    We present results of the deposition of nitrogen compounds formed from lightning (LNO x ) using the global chemical transport Model of Atmospheric Transport and Chemistry¿Max Planck Institute for Chemistry version. The model indicates an approximately equal deposition of LNO x in both terrestrial and oceanic ecosystems, primarily in the tropics and midlatitudes open ocean, despite much higher intensities of lightning flashes above landmasses. The highest values of deposition are due to wet convective deposition, with highest values concentrated in the tropical continents. Nonconvective wet deposition, associated with large-scale weather patterns, occurs over large areas of the ocean amid lower values per square meter, manifesting the long-range transport of NO y , including long-lived species such as HNO3 at high altitudes and PAN. Dry deposition is concentrated primarily above landmasses, yet oceanic deposition over wide areas is still observed. Combined together, the total LNO x deposition exhibits maximal influx values over land, whereas oceanic deposition over wider areas renders the integrated deposition over both ecosystems almost identical. Peaks of terrestrial deposition values (located in Africa, South America, and Asia) show seasonal variability by meridionally penetrating the northern or southern midlatitude following the corresponding summer hemisphere, in accordance with the migration of LNO x production sites. On land, wet and dry deposition rates are more or less equal with a small bias toward wet deposition, whereas above the ocean, wet deposition is markedly higher because of a small water uptake efficiency and relatively small surface roughness. Further work of modeling additional species and obtaining more information on different compounds is required
    Water-side turbulence enhancement of ozone deposition to the ocean
    Fairall, C.W. ; Helmig, D. ; Ganzeveld, L.N. ; Hare, J. - \ 2007
    Atmospheric Chemistry and Physics 2007 (2007)7. - ISSN 1680-7316 - p. 443 - 451.
    dry deposition - boundary-layer - gas-exchange - wind-speed - parameterization - surface - fluxes - trends
    A parameterization for the deposition velocity of an ocean-reactive atmospheric gas (such as ozone) is developed. The parameterization is based on integration of the turbulent-molecular transport equation (with a chemical source term) in the ocean. It extends previous work that only considered reactions within the oceanic molecular sublayer. The sensitivity of the ocean-side transport to reaction rate and wind forcing is examined. A more complicated case with a much more reactive thin surfactant layer is also considered. The full atmosphere-ocean deposition velocity is obtained by matching boundary conditions at the interface. For an assumed ocean reaction rate of 103 s¿1, the enhancement for ozone deposition by oceanic turbulence is found to be up to a factor of three for meteorological data obtained in a recent cruise off the East Coast of the U.S.
    First measurements of H2O2 and organic peroxide surface fluces by the Relaxed Eddy Accumulation technique
    Valverde-Canossa, J. ; Ganzeveld, L.N. ; Rappenglück, B. ; Steinbrecher, R. ; Klemm, O. ; Schuster, G. ; Moortgat, G.K. - \ 2006
    Atmospheric Environment 40 (2006)Suppl. 1. - ISSN 1352-2310 - p. S55 - S67.
    gas-phase ozonolysis - dry deposition - hydrogen-peroxide - hydroxymethyl hydroperoxide - forest canopy - niwot ridge - model - acid - vegetation - chemistry
    The relaxed eddy-accumulation (REA) technique was specially adapted to a high-performance liquid chromatographer (enzymatic method) and scrubbing coils to measure concentrations and fluxes of hydrogen peroxide (H2O2) and organic peroxides with a carbon chain C4, of which only methylhydroperoxide (MHP) and hydroxymethylhydroperoxide (HMHP) were detected. Flux measurements were carried out above the canopy of a Norway spruce forest in Germany (775 m a.s.l.) in NE Bavaria, Germany, during the BEWA2000 research cluster in summer 2001. This period was characterised by H2O2 maximum mixing ratios of 1 ppb and mixing ratios of organic peroxides below 200 ppt. Daily mean H2O2 deposition fluxes of ¿0.8±0.3 nmol m¿2 s¿1, MHP of ¿0.03±0.03 nmol m¿2 s¿1 and HMHP of ¿0.7±0.5 nmol m¿2 s¿1 were obtained. Profile measurements were performed as a qualitative comparison of the controlling mechanism of the surface exchanges. The REA as well as the profile measurements show that during daylight the surface exchanges of H2O2 and MHP over coniferous forest are mainly controlled by dry deposition. The high H2O2 dry-deposition velocity suggests a negligible surface uptake resistance for H2O2, whereas the significantly smaller MHP-deposition velocity indicates a significant surface uptake resistance. However, nighttime surface exchanges of these compounds should be further investigated since the in-canopy ozonolysis reaction is expected to affect exchanges. HMHP REA flux measurements show mainly deposition, whereas the ones based on the profile method suggest in-canopy chemical production
    Evaluation of Peroxide Exchanges over a Coniferous Forest in a Single-Column Chemistry-Climate Model
    Ganzeveld, L.N. ; Valverde-Canossa, J. ; Moortgat, G. ; Steinbrecher, R. - \ 2006
    Atmospheric Environment 40 (2006)Supp.1. - ISSN 1352-2310 - p. S68 - S80.
    reactive trace gases - general-circulation model - red spruce needles - dry deposition - hydrogen-peroxide - flux experiments - ozone - nox - parameterization - emissions
    A single-column chemistry-climate model has been applied to evaluate peroxide exchanges measured over a coniferous forest during the BEWA2000 field campaign, July¿August 2001. Simulations indicate that for suppressed nocturnal turbulent mixing, the H2O2 mixing ratios are sensitive to the representation of sources and sinks, e.g., non-stomatal uptake and chemical transformations, the latter tightly linked to atmosphere¿biosphere NOx exchanges through its control on HO2 production. Comparison of observed and simulated H2O2 fluxes suggests that the commonly applied method to estimate uptake resistances results in a significant underestimation of the dry deposition flux. By using a very small surface uptake resistance, as observed, the modeled surface fluxes are still too low due to an underestimation of the simulated turbulent transport. Further, a reasonable agreement between simulated and observed methylhydroperoxide and hydroxymethylhydroperoxide mixing ratios in and above the canopy air is observed. Our analysis indicates the important role of daytime as well as nocturnal turbulent exchanges, which control the efficiency of dry deposition and downward transport of peroxides that are chemically produced higher up in the boundary layer. In turn, this chemical production depends on the upward transport of emitted precursor gases and their oxidization products. This demonstrates that improved simulations of atmosphere¿biosphere peroxide exchanges rely heavily on improved model representations of boundary layer and canopy turbulent exchanges.
    Coupled carbon-water exchange of the Amazon rain forest. II. Comparison of predicted and observed seasonal exchange of energy, CO2, isoprene and ozone at a remote site in Rondônia
    Simon, E. ; Meixner, F.X. ; Rummel, U. ; Ganzeveld, L.N. ; Ammann, C. ; Kesselmeier, J. - \ 2005
    Biogeosciences 2 (2005)3. - ISSN 1726-4170 - p. 255 - 275.
    atmospheric boundary-layers - organic-compound emissions - dry deposition - tropical forest - monoterpene emission - growth-conditions - temperate forest - deciduous forest - gas-exchange - model
    A one-dimensional multi-layer scheme describing the coupled exchange of energy and CO2, the emission of isoprene and the dry deposition of ozone is applied to a rain forest canopy in southwest Amazonia. The model was constrained using mean diel cycles of micrometeorological quantities observed during two periods in the wet and dry season 1999. Calculated net fluxes and concentration profiles for both seasonal periods are compared to observations made at two nearby towers. The modeled day- and nighttime thermal stratification of the canopy layer is consistent with observations in dense canopies. The observed and modeled net fluxes above and H2O and CO2 concentration profiles within the canopy show a good agreement. The predicted net carbon sink decreases from 2.5 t C ha-1 yr-1 for wet season conditions to 1 t C ha-1 yr-1 for dry season conditions, whereas observed and modeled midday Bowen ratio increases from 0.5 to 0.8. The evaluation results confirmed a seasonal variability of leaf physiological parameters, as already suggested in a companion study. The calculated midday canopy net flux of isoprene increased from 7.1 mg C m-2 h-1 during the wet season to 11.4 mg C m-2 h-1 during the late dry season. Applying a constant emission capacity in all canopy layers, resulted in a disagreement between observed and simulated profiles of isoprene concentrations, suggesting a smaller emission capacity of shade adapted leaves and deposition to the soil or leaf surfaces. Assuming a strong light acclimation of emission capacity, equivalent to a 66% reduction of the standard emission factor for leaves in the lower canopy, resulted in a better agreement of observed and modeled concentration profiles and a 30% reduction of the canopy net flux compared to model calculations with a constant emission factor. The mean calculated ozone flux for dry season conditions at noontime was ˜12 n mol m-2 s-1, agreeing well with observed values. The corresponding deposition velocity increased from 0.8 cm s-1 to >1.6 cm s-1 in the wet season, which can not be explained by increased stomatal uptake. Considering reasonable physiological changes in stomatal regulation, the modeled value was not larger than 1.05 cm s-1. Instead, the observed fluxes could be explained with the model by decreasing the cuticular resistance to ozone deposition from 5000 to 1000 s m-1
    Impact of Amazonian deforestation on atmospheric chemistry
    Ganzeveld, L.N. ; Lelieveld, J. - \ 2004
    Geophysical Research Letters 31 (2004). - ISSN 0094-8276 - 5 p.
    general-circulation model - dry deposition - emissions - parameterization - ozone
    A single-column chemistry and climate model has been used to study the impact of deforestation in the Amazon Basin on atmospheric chemistry. Over deforested areas, daytime ozone deposition generally decreases strongly except when surface wetness decreases through reduced precipitation, whereas nocturnal soil deposition increases. The isoprene and soil nitric oxide emissions decrease although nitrogen oxide release to the atmosphere increases due to reduced canopy deposition. Deforestation also affects vertical transport causing substantial ozone and hydroxyl changes, also depending on soil moisture. The analysis shows that assessment of the impact of land cover and land use changes on atmospheric chemistry requires the development of explicitly coupled chemistry and meteorological models including surface trace gas exchanges, micro-meteorology and the hydrological cycle
    Integrated water pollution assessment of the Ebrié Lagoon, Ivory Coast, West Africa
    Scheren, P.A.G.M. ; Kroeze, C. ; Jansen, F.J.J.G. ; Hordijk, L. ; Ptasinski, K.J. - \ 2004
    Journal of Marine Systems 44 (2004)1-2. - ISSN 0924-7963 - p. 1 - 17.
    north-atlantic ocean - dry deposition - world rivers - nitrogen - phosphorus - precipitation - emissions - nitrate - inputs - wet
    An environmental pollution assessment of the Ebrie lagoon, the largest coastal ecosystem in Western Africa, was executed by applying the Driving force-Pressure-State-Impacts-Response (DPSIR) framework. The domestic and industrial activities in Abidjan and agricultural activities in the wider catchment area were identified as the main driving forces. Two-thirds of Biological Oxygen Demand (BOD) loads and 95% of total nitrogen (N) and phosphorous (P) loads of Abidjan are from domestic effluents, with industry making up the rest. Outside of the direct influence of Abidjan, nutrient levels in the lagoon are governed by the influx of nutrients from the rivers Comoe, Me and Agneby, with nutrient land runoff as the key factors. Total annual N loads to the lagoon for 2000 are estimated at 33 kt, of which 45% from urban sources, 42% from land runoff and 13% from atmospheric deposition. Estimates for P are 2.5 kt, 39%, 48% and 13%, respectively. Scenario analysis has shown that autonomous growth, without pollution reduction measures, would result in an estimated five-fold increase in nutrient inputs to the lagoon over the period 1980-2050. Nutrient concentrations in the lagoon would consequently increase by a factor of 3 1/2, which could escalate to a dramatic level of eutrophication for the complete system. Pollution reduction policies aimed at non-point sources would be most effective in reducing nutrient concentrations. Point-source pollution reduction would improve conditions around Abidjan, but not substantially in the other sections of the lagoon. The approach taken in this study has proven efficient under conditions of relative data scarceness, and sufficiently reliable to allow for policy level conclusions to be drawn. (C) 2003 Elsevier B.V. All rights reserved.
    Uncertainties in the fate of nitrogen I: An overview of sources of uncertainty illustrated with a Dutch case study
    Kroeze, C. ; Aerts, R. ; Breemen, N. van; Dam, D. van; Hoek, K. van der; Hofschreuder, P. ; Hoosbeek, M.R. ; Klein, J. de; Kros, H. ; Oene, H. van; Oenema, O. ; Tietema, A. ; Veeren, R. van der; Verhoeven, H. ; Vries, W. de - \ 2003
    Nutrient Cycling in Agroecosystems 66 (2003)1. - ISSN 1385-1314 - p. 43 - 69.
    nitraten - milieueffect - monitoring - stikstofkringloop - onzekerheid - bronnen - nederland - bodemchemie - emissie - uitspoelen - soil chemistry - nitrates - emission - leaching - environmental impact - monitoring - nitrogen cycle - uncertainty - sources - netherlands - organic-matter accumulation - coastal marine ecosystems - forest ecosystems - oxide production - river-basins - managed grasslands - atlantic-ocean - dry deposition - n2o emission - world rivers
    This study focuses on the uncertainties in the fate of nitrogen (N) in the Netherlands. Nitrogen inputs into the Netherlands in products, by rivers, and by atmospheric deposition, and microbial and industrial fixation of atmospheric N2 amount to about 4450 Gg N y¿1. About 60% of this N is transported out of the Netherlands in products. The fate of the remaining 40%, however, is less clear. We discuss uncertainties in losses to the atmosphere (as ammonia or through denitrification), by leaching and runoff, and in N accumulation in biomass and soils. These processes may account for the fate of about 40% of the N in the Netherlands, and for the fate of about 60% of the N in Dutch agricultural soils. Reducing uncertainties in the estimates of these fluxes is necessary for reducing the impact of excess N in the environment. In particular, monitoring the environmental effects of ammonia emissions and nitrate leaching to groundwater and aquatic systems requires an increased understanding of the fate of N. Uncertainties arise because (1) some N fluxes cannot be measured directly and are usually quantified indirectly as the balance in N budgets, (2) direct measurements of N fluxes have inevitable inaccuracies, (3) lack of experimental data and other information (e.g. statistics) needed for upscaling, (4) large spatial and temporal variability of fluxes, and (5) poor understanding of the processes involved. These uncertainties can be reduced by additional experimental studies and by further development of process-based models and N budget studies. We prioritize these future research needs according to a range of different criteria
    Contribution of aerosol deposition to atmosphere deposition and soil loads into forests.
    Erisman, J.W. ; Draaijers, G.J.P. ; Duyzer, J.H. ; Hofschreuder, P. ; Leeuwen, N. van; Romer, F.G. ; Ruijgrok, W. ; Wijers, C.P. - \ 1994
    Bilthoven : RIVM - 63
    atmosfeer - aërosolen - samenstelling - stof - luchtverontreiniging - luchtkwaliteit - bosbouw - ecologie - bossen - verontreiniging - verzuring - bodem ph - bodemaciditeit - nederland - droge depositie - atmosphere - aerosols - composition - dust - air pollution - air quality - forestry - ecology - forests - pollution - acidification - soil ph - soil acidity - netherlands - dry deposition
    De invloed van atmosferische depositie op diatomeeen en chemische samenstelling van het water in sprengen, beken en bronnen
    Dam, H. van; Mertens, A. ; Janmaat, L.M. - \ 1993
    Wageningen : DLO-IBN (IBN - rapport 052)
    rivieren - waterlopen - kanalen - oppervlaktewater - rivierwater - chemische samenstelling - neerslag - chemische eigenschappen - zuurgraad - zure regen - bacillariophyta - verontreiniging - waterorganismen - nederland - droge depositie - biologische eigenschappen - rivers - streams - canals - surface water - river water - chemical composition - precipitation - chemical properties - acidity - acid rain - bacillariophyta - pollution - aquatic organisms - netherlands - dry deposition - biological properties
    The flux of ozone to a maize crop and the underlying soil during a growing season
    Pul, W.A.J. van - \ 1992
    Agricultural University. Promotor(en): L. Wartena; A.F.G. Jacobs. - S.l. : Van Pul - 147
    agrometeorologie - zea mays - maïs - ozon - droge depositie - agricultural meteorology - zea mays - maize - ozone - dry deposition

    To observe the flux or deposition of ozone above a maize crop, experiments were carried out during the growing season of maize in 1988. The flux of ozone was determined using meteorological techniques. The measurements used in the present study were carried out under atmospheric conditions in which the vertical divergence of the flux of ozone was the dominant term in the mass conservation equation of ozone. That is, under such conditions, the flux measured at a certain height served as a good estimate of the flux at the surface. This was demonstrated in chapter 2 by a scaling exercise of the mass conservation equation and the time dependency of the flux of ozone in order to reveal the importance of the various terms in the equations. The second important term in this scaling is the chemical reactions which produce and destroy ozone (section 2.1.1). However, an accurate estimate of this influence could not be given at first hand. More accurate estimates were made with a model which describes the vertical divergence of the flux of ozone and nitrogen oxides. By scaling the equation of the local time derivative of the flux of ozone (section 2.1.3) it was found that the gradient production and pressure fluctuation term were much larger than the chemical reaction term. From this scaling and the model calculations it was concluded that the chemical reactions did not severely influence the flux of ozone.

    Three meteorological techniques were used to assess the flux of ozone: the eddy correlation technique, the profile technique and the modified Bowen ratio technique. The theoretical background to these techniques was given in chapter 2. Chapter 3 and 4 presented the experimental outline and the accuracy of the measurements, respectively.

    It was found that the accuracies of the fluxes were strongly determined by the errors in the differential measurements or the profiles of the variables. The accuracy of the flux of ozone measured with the profile technique was 20-53%. For the modified Bowen ratio technique this was 13-58%. The accuracy of the eddy correlation fluxes was about 20%. 'Ibis was mainly caused by the intermittency of the flux in the 30 min time interval over which they were averaged.

    A comparison between the three techniques was made for nine days. The profile technique gave systematically lower values for the flux of ozone than the eddy correlation and modified Bowen ratio techniques. A reduction of about 40% of the flux of ozone was found, calculated from the ozone concentration at 6 z om + d and 30 z om + d, during near-neutral and unstable atmospheric conditions. This was caused by a) an inadequate use of the profile technique close to the roughness elements and b) an uncertertainty in the displacement height for ozone. The flux of ozone determined with the modified Bowen ratio technique was moderately consistent with that determined with the eddy correlation technique and no systematic deviations were found. This indicates that: a) the modified Bowen ratio technique is applicable close to the surface, b) sensible and latent heat (water vapour) are transported in. roughly the same way and c) chemical reactions did not cause large systematic deviations, i.e. no large flux divergence between the two techniques existed though the fluxes were measured at different heights.

    The time integrals over the day of the fluxes of ozone derived with the modified Bowen ratio and the eddy correlation techniques agreed very well. This means that a reliable estimate of the daytime deposition of ozone (accuracy ±10%) was obtained using these techniques. The accuracy of the 30 min values, however, is much smaller (20-50%).

    In chapter 5 a resistance model was used to deduce the ability of the surface to destroy ozone, expressed in the surface resistance, from the flux measurements. This was done for bare soil as well as the crop - soil system as a whole when the soil was entirely covered by the crop. The resistance of the soil to ozone was dependent on the soil water content, i.e. the soil surface resistance increased with increasing soil water content.

    In the evaluation of the magnitude of the different parallel sinks of ozone such as the stomata and the soil surface, the conductances of the surface and the crop to ozone were used. An estimate on the crop conductance to ozone i.e. the stomatal uptake of ozone, was made using the analogy to the transpiration of the crop.

    The surface conductance to ozone was mainly determined by the uptake of ozone by the stomata, the destruction at the soil surface and the transport towards the soil. When the soil surface is wet (i.e. rainfall occurred a few hours prior to the measurements) the surface conductance and the crop conductance to ozone coincided.

    The conductance of the remaining plant parts (mainly the cuticle) to ozone was small compared to the stomatal or soil conductance to ozone.

    The exchange of ozone with the soil was mainly determined by the turbulent mixing (expressed by the friction velocity), the stability of the air above the crop and the leaf area density.

    When the soil surface is not wet (i.e. no rainfall a day before the measurements), the flux of ozone towards the soil can be 25-50% of the total flux of ozone. In such circumstances the flux of ozone should be modelled using a surface resistance in which the soil resistance to ozone, as well as an in- crop aerodynamic resistance are incorporated. This in-crop aerodynamic resistance depends among others on the turbulent mixing above the crop and the leaf area density.

    A more quantitative analysis of the exchange of ozone with the crop and the underlying soil can be made by using more complex canopy flow models such as those by Meyers and Hicks (1988), Li et al., (1985). In such models the non-local transport of momentum and scalars are described. With these models a more detailed sink distribution of ozone in the crop can also be made using, for instance, measured profiles of ozone in the crop (Raupach, 1989). Another outcome of these models can be a parameterization of the in-crop aerodynamic resistance for use in air pollution dispersion models.

    In chapter 6 an overview of the deposition of ozone and the governing factors during the growing season of maize were presented. The total deposition of ozone calculated as the time integral of the flux over the entire day, varied from 5-50 mg m -2, with an average of 19.0 mg m -2. The daytime deposition accounted for on average 83% of the total deposition. The deposition during night-time was small compared to the total deposition (17%). The total deposition showed a seasonal pattern. This pattern is largely caused by the seasonal pattern of the concentration of ozone. This is illustrated by the findings that the daytime deposition of ozone can be well estimated by the average concentration of ozone. A better estimate is obtained if the time period is included over which the flux is calculated i.e. the dose of ozone. The main reason for this good estimate is the relatively small fluctuations in the mean daytime surface conductance to ozone. The best estimate of the daytime deposition of ozone is obtained by using the average values of the concentration, the deposition velocity and the time period. This value gives a small underestimate (10%) of the daytime deposition due to some loss in correlation between the deposition velocity and the concentration.

    The uptake by the crop varied from 2.8 - 25.2 mg m -2, with an average of 12.8 mg m -2. This uptake was 50-100% of the daytime deposition of ozone, with an average of 86%. This uptake can be reasonably estimated with the dose of ozone.

    To reveal a seasonal trend in the uptake of ozone by the crop, a data series of at least several growing seasons is necessary to obtain full coverage on all wind directions and environmental situations in which the crop was grown. It is especially the coupling of these data to the effects on plants such as a reduction in crop yield that requires very long data series, since the climatic 'noise' on these data is very large. Therefore a more appropriate approach would be to evaluate all available measurements in this field by means of coupled flow - crop growth models. This data set can be used, for example, to verify such models in which the exchange of air pollutants with the crop and the soil is described.

    Effects of NH3 and (NH4)2SO4 deposition on terrestrial semi-natural vegetation on nutrient-poor soils
    Eerden, L.J. van der; Dueck, T.A. ; Elderson, J. - \ 1990
    Wageningen etc. : IPO [etc.] (IPO report R 90/06) - 311
    luchtverontreiniging - ammoniak - atmosfeer - chemicaliën - klimaatfactoren - bosschade - bosbouw - heidegebieden - nederland - plantengemeenschappen - planten - sulfaten - bomen - vegetatie - pinus sylvestris - droge depositie - air pollution - ammonia - atmosphere - chemicals - climatic factors - forest damage - forestry - heathlands - netherlands - plant communities - plants - sulfates - trees - vegetation - pinus sylvestris - dry deposition
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