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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    Plaagbestrijding in de tropen: wedden op meer paarden
    Huis, A. van - \ 2008
    In: Natuur als Bondgenoot / Osse, J.W.M., Schoonhoven, L.M., Dicke, M., Buiter, R., Den Haag : Stichting Bio-Wetenschappen en Maatschappij (Cahiers bio-wetenschappen en maatschappij 4) - ISBN 9789073196490 - p. 57 - 64.
    geïntegreerde bestrijding - organismen ingezet bij biologische bestrijding - plagenbestrijding - insecten - genetische modificatie - biologische bestrijding - chemische bestrijding - tropen - sprinkhanen - akkerbouw - vollegrondsgroenten - integrated control - biological control agents - pest control - insects - genetic engineering - biological control - chemical control - tropics - locusts - arable farming - field vegetables
    Door de groei van de - steeds veeleisender - wereldbevolking, rijst de vraag naar landbouwproducten de pan uit. Daarom zullen boeren steeds grootschaliger gaan werken, ook in de tropen. Risico's op grootschalige plagen horen daarbij. 'Zeker in de tropen zul je die plagen op een diverse en geïntegreerde manier moeten bestrijden', zegt professor Arnold van Huis, hoogleraar tropische entomologie aan de Wageningen Universiteit
    La Cordillera Oriental Colombiana, Transecto Sumapaz
    Hammen, T. van der; Rangel, J.O. ; Cleef, A.M. - \ 2008
    Berlin-Stuttgart : J. Cramer (Studies on tropical Andean ecosystems vol. 7) - ISBN 9783443500320 - 1009
    ecosystemen - tropen - vegetatie - bossen - natuurbescherming - colombia - andes - ecosystems - tropics - vegetation - forests - nature conservation - colombia - andes
    The publication of this volume (volume 7) concludes the publication of the study of the Transects of Buritaca (Sierra Nevada de Santa Marta), Parque Los Nevados (Cordillera Central), Tatamá (Western Cordillera) and Sumapaz (Eastern Cordillera) in the Colombian Andes. The latter three studies represent a West-East transect through the Colombian Andes, from the Pacific to the Llanos Orientales (Eastern Plains) at an approximate latitude of 4 ° North.
    Review of carbon flux estimates and other greenhouse gas emissions from oil palm cultivation on Tropical peatlands - Identifying the gaps in Knowledge
    Verwer, C.C. ; Meer, P.J. van der; Nabuurs, G.J. - \ 2008
    Wageningen : Alterra (Alterra-rapport 1731) - 44
    oliepalmen - bosplantages - koolstofcyclus - veengebieden - tropen - maleisië - luchtverontreiniging - oil palms - forest plantations - carbon cycle - peatlands - tropics - malaysia - air pollution
    This report provides an independent review that clarifies current confusion on carbon dioxide emissions resulting from oil palm cultivation on tropical peatlands in Malaysia, that was brought about by two recent publications. It describes the processes of carbon flow in forests, degraded forests and oil palm plantations on peat and depicts uncertainties in existing datasets. The report identifies the gaps of knowledge and offers recommendations for further research to be commissioned by the Joint Committee on Carbon Emissions (JCCE), Malaysia-The Netherlands
    Forest plantations for sustainable production in the tropics : key issues for decision-makers
    Bodegom, A.J. van; Berg, J. van den; Meer, P.J. van der - \ 2008
    Wageningen : Wageningen University & Research centre (Publicatie / Wageningen International ) - ISBN 9789085852315 - 34
    bosplantages - duurzaamheid (sustainability) - besluitvorming - agroforestry - bosbouw - bosbeleid - biodiversiteit - subsidies - certificering - tropen - forest plantations - sustainability - decision making - agroforestry - forestry - forest policy - biodiversity - subsidies - certification - tropics
    PRIMET version 2.0, technical description and manual : a decision support system for assessing Pesticide RIsks in the tropics to Man, Environment and Trade
    Peeters, F.M. ; Brink, P.J. van den; Vlaming, J. ; Groenwold, J.G. ; Beltman, W.H.J. ; Boesten, J.J.T.I. - \ 2008
    Wageningen : Alterra (Alterra-rapport 1648) - 77
    pesticiden - gezondheid - blootstelling - risicoschatting - groenten - tropen - ontwikkelingslanden - milieueffect - beslissingsondersteunende systemen - pesticides - health - exposure - risk assessment - vegetables - tropics - developing countries - environmental impact - decision support systems
    Pesticide exposure via for instance spray drift or runoff to surface water, accumulation in the topsoil, and leaching to groundwater potentially affects organisms in water, in and around soil and on plants and might also pose risks to humans via dietary exposure, in case they consume contaminated products like groundwater, macrophytes and fish. To estimate these risks at the household level the PRIMET Decision Support System was developed. PRIMET runs with a minimum of input data and is developed to be used in developing countries
    Dynamics of secondary forests
    Breugel, M. van - \ 2007
    Wageningen University. Promotor(en): Frans Bongers, co-promotor(en): M. Ramos. - [S.l.] : S.n. - ISBN 9789085046936 - 240
    secundaire bossen - bossen - plantensuccessie - populatiedynamica - bosecologie - vegetatie - landbouwgronden - verlaten grond - tropen - mexico - secondary forests - forests - plant succession - population dynamics - forest ecology - vegetation - agricultural soils - abandoned land - tropics - mexico
    The succession of tropical secondary forests on abandoned agricultural fields has been studied since long, most often by comparing stands of different age since abandonment. These so-called chronosequence studies have yielded much insight in general patterns of succession and the constraints and conditions that affect the course of succession (shortly reviewed in chapter 1). Successional dynamics, however, are inferred rather than directly monitored in such studies; i.e. direction and rates of change of community structure and composition are deduced indirectly on the assumption that similar successional processes take place in any one stand. Only very few studies followed successional dynamics through repeated measurements in permanent sample plots, hence our current understanding of the variation in successional dynamics across secondary forest stands, the underlying processes of growth, mortality and recruitment, and the processes and mechanism that steer them, is still poor.

    This thesis presents data from one of the very few studies on secondary tropical forest succession in multiple permanent sample plots. The focus of this work is on the first years of secondary forest succession, and on the role of competition on the level of individuals, populations and communities. The main aims of this work were: 1) To evaluate the dynamics of young secondary forests on abandoned agricultural fields in terms of rates and direction of community changes, how these dynamics vary across sites and how they change with time since abandonment; 2) To evaluate the dynamics of young secondary forests in terms of growth, mortality and recruitment, and how community changes are related to these processes; and 3) To examine the degree to which competition for light can account for variation in growth and mortality of saplings within a population and for variation in population dynamics across distinct sites.

    The study was carried out in three villages in theMarquésdeComillas(MdC) region, part of theSelvaLacandonain easternChiapas,Mexico. The climate of theMdCregion is humid tropical, with an average annual temperature of 24 ºC, mean annual rainfall of ~3000 mm and a short dry period in February-April. The original vegetation consists mainly of tropical evergreen and semi-deciduous forests. Colonization of the region started in the late 1960s, and since then a large part of the landscape has been converted to a mosaic of temporary and permanent grazing pastures, cultivated land, young secondary forest and old-growth remnants. The prevailing land use types in the three villages are slash-and-burn shifting cultivation practices (mainly maize) with short fallow periods and semi-permanent cattle ranging.

    Data for this study were collected in secondary forests on abandoned agricultural fields and pastures with time since abandonment (age) ranging from 0.5 to 18 years. A first dataset consisted of a chronosequence of 72 stands, widely distributed over an area of roughly 60 km2 and encompassing differentgeomorphologicalunits (low hills vs. alluvial planes) and former land-use types (abandoned agricultural fields vs. pastures). In each stand, three 2 x 25 m transects were randomly located in which all woody stems with diameter at 1.3-m above ground (dbh) ≥ 1 cm identified to lowest possibletaxonand their dbh and height were measured. A second dataset consists of permanent sample plots in twelve secondary forests with similar former land-use (maize fields) and geomorphology (low hills with sandy acidic and unfertile soils). Initial stand age ranged from 1-17 y. In each stand a 10 x 50-m permanent sample plot is established, and all trees with height ≥ 1.5-m are recorded, and tagged. Location of each tree was determined using a 1 x 1-m grid system. Every year dead trees and new recruits are recorded and dbh and height of all living trees is (re-)measured. The first dataset is used in chapter 2, and in chapters 3-7 data are used from the first three years of permanent plot study.

    Chapter 2 demonstrates that patterns of species diversity, frequency and dominance are highly variable across secondary forests of an agricultural landscape, even when they are of similar age. Diversity varied widely between the plots, which could only partly be explained by differences in time since abandonment and geomorphology while the influence of former land use was even more ambiguous. Species richness changed with age, but dominance levels remained similar over the first 18 year of succession. Similarly, species richness, but not dominance, differed between secondary forests on low hills and alluvial plains. Across-stand frequency and abundance patterns varied strongly among tree species, and most among pioneer species. Despite the high species richness (almost 200 species identified across all plots), only a very small sub-set of the regional species pool dominated secondary forests in terms of frequency of occurrence and abundance, all of them pioneer species. Most pioneer species, however, and nearly all shade tolerant species, occurred in less than 15% of the plots and always in low densities. Only two species (Cecropia peltata and Trichospermum mexicanum) occurred in ≥ 50% of the plots and they were also the only species that were relatively dominant (> 10 stems / > 10% of stand basal area) in ≥ 20% of the plots. Other species were dominant (> 10% basal area) in the plots were they occurred, but never abundant (e.g.Ochromapyramidale); frequent but never abundant (e.g.Vernoniapatens); or locally abundant but with low relative basal area (e.g.Acalyphadiversifolia).

    The "Initial Floristic Composition" hypothesis predicts that, on abandoned agricultural fields with light previous land-use and close to seed sources, both pioneer and shade-tolerant species colonize a site directly after abandonment and that the recruitment of pioneers sharply declines while the recruitment of shade-tolerant species continues as soon as the canopy closes. It also predicts higher mortality among pioneers. Consequently, recruited and dead trees are expected to differ in species composition, with highest species richness for the recruits. To evaluate these predictions, recruitment and mortality was examined in eight permanent sample plots with initial fallow age of 1 to 5 y (chapter 3). Shade-tolerant species established in the first years of succession, albeit in low numbers. As predicted, recruited and dead trees differed in species richness and composition, and in shade-tolerant frequency. In contrast to expected, over 50% of recruits were from pioneer species. Results suggested that high stand-level mortality opened new opportunities for continued pioneer colonization. Results demonstrate that species turnover starts very early in succession but is not always a gradual and continuous process, complicating prevailing succession models.

    In chapter 4, stand structure dynamics (i.e, rate and direction of stand structure changes) were related to mortality, growth, and recruitment rates over a two-year period, and the dependence of these demographic processes on fallow age and initial stand structure attributes was evaluated. Changes in stand structure were especially fast in the first 5 y of succession, and decreased rapidly afterwards, which resulted from similar stand-level changes in relative mortality, growth, and recruitment rates. Changes in most stand structure attributes (e.g. basal area, canopy height) were closely correlated, and more linked with tree growth rates than with net changes in tree density due to recruitment and mortality. Demographic processes were negatively related with initial stand basal area, but independent of initial tree density. Results suggest that asymmetric competition and resulting patterns of size and density dependent mortality and growth are major driving forces determining secondary forest successional pathways. Sudden mass mortality among dominant species in some stands showed that early secondary forest succession is not always a gradual and unidirectional process.

    The strong spatial and temporal variability of successional dynamics emphasizes the need to monitor these dynamics in permanent plots across a range of initial stand ages, with multiple plots in a given age class. In chapter 5, case studies inCosta RicaandMexicoshow that the actual rates of change in tree communities often deviate from chronosequence trends. With respect to tree species composition, sites of different agesdiffermore than a single site followed over time through the same age range. While changes in stem density have little to do with chronosequence trends, changes in basal area within stands generally followed chronosequence trends. Stem turnover rates were poor predictors of species turnover rates, particularly at longer time-intervals. Effects of the surrounding landscape on tree community dynamics within individual plots were not specifically included in this or in any of the other chapters, but results suggest that they are likely to be important determinants of species accumulation rates and relative abundance patterns.

    Competition for light is often considered to be one of the main mechanisms that regulate successional vegetation dynamics. Competition for light is largely asymmetric, as larger trees shade smaller trees and not the other way around. Consequently, within-site variation in growth and survival of tree saplings can be expected to relate to variation in the degree of neighborhood competition, especially from the larger neighbors. In chapter 6, these hypotheses were tested for Cecropia peltata and Trichospermum mexicanum saplings in two adjacent 1-2 year old secondary forest stands. The degree of competition was estimated by neighborhood basal area (NBA). Both diameter and height growth were strongly negatively related to NBA of the larger neighbors. Only a small proportion of variation in survival, on the other hand, could be accounted for by variation in NBA, suggesting that other factors are more important. The effect of NBA of smaller neighbors on growth and survival was very weak or non-significant, indicating that competition between neighbors, indeed, is largely asymmetric.

    Population dynamics of a species vary much from one secondary forest to another. In chapter 7 we examined if such between-site differences in demographic behavior can be related to variation in asymmetric competition that result from differences in stand and population size structures. Specifically, we tested if differences in mean growth and mortality of the biggest and of the smallest trees of a population (growth and survival asymmetry) were related to differences in the average level of asymmetric neighborhood competition in both size groups (competition asymmetry). We used 24 populations of four pioneer tree species in nine early (1-5 y) secondary forest stands. For each population, we compared average neighborhood basal area, growth and survival of the twenty percent smallest and twenty percent largest trees. The between-plot variation in competition asymmetry explained a significant part of the between-plot variation in growth asymmetry, with smallest trees growing faster in populations with low competition asymmetry, and largest trees growing fastest in populations with high competition asymmetry. Survival was size-related, with lowest survival rates among the smallest plants, as expected. However, survival asymmetry was significantly related to competition asymmetry in just one species. The differences in

    theeffects of asymmetric competition on the mortality and survival of the four species show that susceptibility to competition for, presumably, light, varies considerably between early successional pioneer species. Results of chapter 6 and 7 support the prediction that in young secondary forests, asymmetric competition for light is one of the main mechanisms that govern secondary forest dynamics.

    Improving productivity in tropical lakes and reservoirs
    Kolding, J. ; Zwieten, P.A.M. van - \ 2006
    Cairo : WorldFish Center (Aquatic Ecosystems and Fisheries Review Series 1. Theme 3 of CPWF. 1) - ISBN 9789771730873 - 139
    meren - visproductie - visserijbeheer - reservoirs - tropen - aquatische ecosystemen - lakes - fish production - fishery management - reservoirs - tropics - aquatic ecosystems
    Diagnose van problemen met potplanten geteeld uit tropisch uitgangsmateriaal
    Weening, K. ; Leeuwen, G.J.L. van - \ 2005
    Naaldwijk : PPO BU Glastuinbouw (Rapporten BU Glastuinbouw ) - 26
    vegetatieve vermeerdering - vermeerderingsmateriaal - potplanten - sierplanten - tropen - vegetative propagation - propagation materials - pot plants - ornamental plants - tropics
    In Nederland doen zich in toenemende mate problemen voor met de afkweek van potplanten, waarvan het uitgangsmateriaal afkomstig is uit tropische gebieden. Vooral landen in Midden Amerika nemen hierbij een voorname plaats in. Een belangrijke aanleiding van de problemen is dat de groothandel en andere afnemers steeds stringentere eisen stellen aan kwaliteit en uniformiteit. Gedreven door stagnerende opbrengstprijzen en stijgende kosten moeten (Nederlandse) teelt bedrijven in staat zijn om tijdens een steeds kortere periode te kunnen afkweken. De afhankelijkheid van de kwaliteit van het geïmporteerde materiaal wordt hiermee vergroot. Optimalisering van de gehele keten is noodzakelijk om de centrale positie van Nederland in de teelt en handel te behouden.
    Optimization of water management in polder areas
    Wandee, P. - \ 2005
    Wageningen University. Promotor(en): E. Schultz, co-promotor(en): T. Tingsanchali. - S.l. : s.n. - ISBN 9780415375559 - 397
    polders - waterbeheer - simulatiemodellen - drainage - optimalisatie - tropen - humide tropen - geografische informatiesystemen - polders - water management - simulation models - drainage - optimization - tropics - humid tropics - geographical information systems
    Water management in polders in The Netherlands, compared with water management in Thailand. With the Dutch case studies: Schieveen, Duifpolder, Hoge en Lage Abtswoudse polder
    La Cordillera Occidental Colombiana. Transecto Tatamá
    Hammen, T. van der; Rangel, J.O. ; Cleef, A.M. - \ 2005
    Berlin : J. Cramer (Studies on tropical Andean ecosystems vol. 6) - ISBN 9783443500283 - 956
    ecosystemen - tropen - vegetatie - bossen - natuurbescherming - colombia - andes - ecosystems - tropics - vegetation - forests - nature conservation - colombia - andes
    This volume 6 of the series Studies on Tropical Andean Ecosystems, contains the results of the Colombian Western Cordillera around latitude 5° N. The fieldwork was realized in 1983. The transect consists of two parts, the first between 500 m and 2150 m altitude located slightly South of 5° N, at the latitude of San José del Palmar, and the other slightly North of 5° N, at the latitude of Santuario and the Tatamá massif, between 2150 and 4200 m altitude. The total transect was therefore named: "The Tatamá transect".
    PRIMET Version 1.0, manual and technical description; a decision support system for assessing pesticide risks in the Tropics to man, environment and trade
    Brink, P.J. van den; Horst, M.M.S. ter; Beltman, W.H.J. ; Vlaming, J. ; Bosch, H. van den - \ 2005
    Wageningen : Alterra (Alterra-report 1185) - 60
    pesticiden - gezondheid - blootstelling - risicoschatting - groenten - tropen - ontwikkelingslanden - milieueffect - beslissingsondersteunende systemen - pesticides - health - exposure - risk assessment - vegetables - tropics - developing countries - environmental impact - decision support systems
    Pesticide exposure via for instance spray drift or runoff to surface water, accumulation in the topsoil, and leaching to groundwater potentially affects organisms in water and soil and might also pose risks to humans via dietary exposure, in case they consume contaminated aquatic products like groundwater, macrophytes and fish. To estimate these risks at the household level the PRIMET Decision Support System was developed. PRIMET runs with a minimum of input data and is developed to be used in developing countries. The risk assessment is expressed in Exposure Toxicity Ratio’s which are calculated by dividing the predicted exposure by the safe concentration. This report provides a mathematical description of the processes incorporated into PRIMET and a user manual. PRIMET is freely available at
    Breeding objectives and breeding strategies for small ruminants in the tropics
    Kosgey, I.S. - \ 2004
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): J.P. Gibson. - [S.l.] : S.n. - ISBN 9789058089908 - 272
    schapen - geiten - herkauwers - dierveredeling - doelstellingen - veredelingsprogramma's - kleine landbouwbedrijven - pastoralisme - tropen - sheep - goats - ruminants - animal breeding - objectives - breeding programmes - small farms - pastoralism - tropics
    Small ruminants (i.e., sheep and goats) are widespread in the tropics and are important to the subsistence, economic and social livelihoods of a large human population in these areas. The aim of this thesis was to identify the breeding objectives for tropical small ruminants, and to develop appropriate breeding strategies for their improvement. The results indicated that breed substitution and crossbreeding programmes involving temperate breeds are rarely successful due to incompatibility of the genotypes with the farmers' breeding objectives and the production systems. Within-breed selection programmes utilizing indigenous breeds are likely to be more sustainable than breed substitution and crossbreeding. In addition, they help to maintain biodiversity. Indigenous genotypes were predominantly found among pastoral/extensive farmers and mixed crosses among smallholders. In general farmers perceived crosses less favourably than indigenous breeds for a range of traits. The effect was studied of including intangible benefits in the calculation of economic values of breeding goal traits. It resulted in increased values of traits related to longevity. Litter size and lambing frequency were more important traits in smallholder and pastoral production. 12-month live weight also featured prominently in pastoral production. Constraints to small ruminant productivity included low levels of management, disease and parasite challenge, inadequate feed and poor marketing. Nucleus breeding schemes are recommended to optimize the limited available resources. However, 'interactive cycling screening' schemes would be more practical under village settings as the farmers are actively involved in genetic improvement, and minimal recording is required in the commercial flocks. A single nucleus could serve both the smallholder and pastoral production. In conclusion, it is prudent to examine the production system holistically, and involve the producer at every stage in the planning and operation of a breeding programme, integrating traditional knowledge, practices, behaviour and values.
    "Wegwijzers in de jungle"
    Bongers, F. - \ 2003
    Wageningen : Wageningen Universiteit - 40
    tropische bossen - bossen - tropen - bosecologie - bosbedrijfsvoering - conservering - bescherming - openbare redes - tropical forests - forests - tropics - forest ecology - forest management - conservation - protection - public speeches
    Soil Fertility Decline in the Tropics with Case Studies on Plantations
    Hartemink, A.E. - \ 2003
    Wallingford : CAB International / ISRIC - ISBN 9780851996707 - 360
    bodemvruchtbaarheid - bodemdegradatie - tropische gronden - plantagegewassen - beplantingen - tropen - soil fertility - soil degradation - tropical soils - plantation crops - plantations - tropics
    This book, containing 12 chapters including an introduction which focuses on soil fertility under different land use systems in the tropics. Chapter 2 contains a global literature review on human population growth, soil resources of the tropics, tropical land use and management, soil degradation and sustainable land management. Chapter 3 reviews historical and productivity aspects of agricultural plantations in the tropics. Chapter 4 covers theoretical considerations of soil fertility decline and includes sections on data requirements, spatial and temporal variation, soil tests and interpretation of soil fertility decline studies. Chapter 5 focuses on soil fertility decline of annual cropping systems and brings together a wide range of data and studies. Soil changes under plantation crops are critically examined in Chapters 6 to 10 using published literature on perennial crops, sugarcane plantations and forest plantations. Two detailed case studies are included, based on research conducted at plantations in Tanzania and Papua New Guinea. Chapter 11 synthesizes data from the literature and the case studies. Finally, a summary of the soil changes followed by some of the implications for plantation cropping and a set of conclusions is given in Chapter 12.
    A model study on population dynamics of Striga that can infect a newly developed resistant Sorghum crop, with practical guidelines to safeguard the sustainability of resistant Sorghum varieties
    Kempenaar, C. ; Davies, J.A.R. ; Scheepens, P.C. - \ 2003
    Wageningen : Plant Research International (Note / Plant Research International 259) - 21
    striga hermonthica - striga - parasitaire planten - onkruiden - populatiedynamica - genetisch bepaalde resistentie - sorghum bicolor - zaadbanken - teeltsystemen - simulatiemodellen - tropen - striga hermonthica - striga - parasitic plants - weeds - population dynamics - genetic resistance - sorghum bicolor - seed banks - cropping systems - simulation models - tropics
    Towards sustainable and robust on-site domestic wastewater treatment for all citizens
    Mgana, S. - \ 2003
    Wageningen University. Promotor(en): Gatze Lettinga, co-promotor(en): W.T.M. Sanders. - [S.I.] : S.n. - ISBN 9789058087645 - 95
    afvalwaterbehandeling - anaërobe behandeling - haalbaarheidsstudies - tropen - waste water treatment - anaerobic treatment - feasibility studies - tropics

    In most developing countries commonly practiced domestic wastewater treatment systems predominantly constitute anaerobic treatment process. The anaerobic treatment units mostly installed are on-site at residential dwellings.

    However the commonly installed units, viz., traditional pit latrines and septic tanks are in fact 'low-rate' anaerobic pre-treatment units and are associated with inefficiency, poor maintenance and groundwater pollution. Moreover since most poor communities, who constitute the majority in the developing countries' populations could afford these types of anaerobic pre-treatment units, their numbers have also grown to unmanageable proportions. Consequently the demand for effective but low cost wastewater treatment facilities for developing countries is indisputably great.

    On the basis of already available technical information concerning the Upflow Anaerobic Sludge Bed (UASB) reactor performance a wastewater treatment system based on the UASB reactor can lead to a compact, effective and low cost community on-site pre-treatment unit for tropical wastewaters. However the performance of these systems in an actual community on-site situation has so far not been investigated. This thesis therefore investigates the performance and feasibility of using the UASB reactor for the pre-treatment of wastewater under the conditions that arise at community level in tropical regions, viz. highly varying organic and hydraulic loads, but low variation in temperature.

    On-site pilot scale UASB reactors were configured and operated in parallel at community level for the purpose of acquiring performance data. All the reactors were operated in gravity flow mode at ambient tropical temperature of 25 - 34 ºC. The wastewater in the study area - community level - was highly biodegradable with an average ratio COD:BOD 5 of 1.52 at a standard deviation of 0.13. The wastewater characteristic was highly variable. A 1277-day monitoring duration of the wastewater grab samples has shown that the values of organic loads (with standard deviation in brackets), in terms of COD tot , and COD ss , were 529.4 (544.6) and 264.4 (448.4) mg/L respectively.

    A conventional pilot single-step community on-site UASB reactor (volume: 1.5 m 3, height: 1.7 m) was operated over three and a half years at an average hydraulic retention time of 6.2 (4.92). The performance data obtained via regular monitoring of the treatment unit showed a declining removal efficiency over time with respect to COD total , which likely can be attributed to the increasing rate at which biogas was produced along with the growth of sludge bed and the presence of floating sludge. As a result the removal of dispersed sludge particles becomes poorer, which likely is reinforced by the possible 'less' optimal dimensions and design of the Gas-Solids-Separator (GSS) device. The average removal efficiency on COD tot basis was 64 percent. However a study of a parallel pilot two-step community on-site UASB reactor configuration gave more promising results. The two-step UASB pre-treatment unit in this research refers to two UASB reactors connected in series, viz. a first 2m high 1.8m 3UASB reactor put in front of a second 1m high 0.852 m 3UASB reactor. The second-step UASB reactor is a recipient of effluent including washouts from the first-step UASB reactor The average organic loads of the wastewater imposed to the system with respect to COD fractions COD tot , COD ss , COD col and COD sol were 537.2 (165.3), 189.9 (109.5), 127.4 (75) and 223.4 (108.8) respectively. The investigations were conducted over a period of 630 days. The overall removal efficiency obtained on the basis of the distinguished COD fractions was far better than for the individual reactors, i.e efficiencies for COD tot , COD ss , COD col and COD sol , were respectively 68.7 (16.7), 51.2 (41.8), 62.1(38.2), and 71.8 (30.5) %. The imposed overall HRT was 7.4 (1.6) (i.e. 5 + 2.4) hours. The advantages of the two-step UASB reactor configuration include 1) the distinct higher overall removal efficiency of the anaerobic pre-treatment system 2) the higher sludge age 3) the higher reliability of the anaerobic pre-treatment process 4) the two reactors can separately be operated in case of technical problems.

    Economic valuation of forests and nature : a support tool for effective decision making
    Lette, H. ; Boo, H. de - \ 2002
    Wageningen etc. : International Agricultural Centre [etc.] (Theme studies series / Forests, forestry and biodiversity support group 6) - 69
    bossen - natuurbescherming - taxatie - bosbouweconomie - besluitvorming - kosten-batenanalyse - tropen - natuur - forests - nature conservation - valuation - forest economics - decision making - cost benefit analysis - tropics - nature
    Included are several case studies, like: The Leuser ecosystem, Sumatra; The Borivili National Park, India; Tropical rain forests, Costa Rica; Mangrove forests, Philippines. This document has been prepared by: IAC and EC-LNV
    Acclimation of photosynthetic capacity to irradiance in tree canopies in relation to leaf nitrogen concentration and leaf mass per unit area
    Meir, P. ; Kruijt, B. ; Broadmeadow, M. ; Barbosa, E. ; Kull, O. ; Carswell, F. ; Nobre, A. ; Jarvis, P.G. - \ 2002
    Plant, Cell & Environment 25 (2002)3. - ISSN 0140-7791 - p. 343 - 357.
    bos - fotosynthese - regenwoud - tropen
    The observation of acclimation in leaf photosynthetic capacity to differences in growth irradiance has been widely used as support for a hypothesis that enables a simplification of some soil-vegetation-atmosphere transfer (SVAT) photosynthesis models. The acclimation hypothesis requires that relative leaf nitrogen concentration declines with relative irradiance from the top of a canopy to the bottom, in 1 : 1 proportion. In combination with a light transmission model it enables a simple estimate of the vertical profile in leaf nitrogen concentration (which is assumed to determine maximum carboxylation capacity), and in combination with estimates of the fraction of absorbed radiation it also leads to simple 'big-leaf' analytical solutions for canopyphotosynthesis. We tested how forests deviate from this condition in five tree canopies, including four broadleaf stands, and one needle-leaf stand: a mixed-species tropical rain forest, oak (Quercus petraea (Matt.) Liebl), birch (Betula pendula Roth), beech (Fagus sylvatica L.) and Sitka spruce (Picea sitchensis (Bong.) Carr). Each canopy was studied when fully developed (mid-to-late summer for temperate stands). Irradiance (Q, ~S^~mol m-2 s-1) was measured for 20 d using quantum sensors placed throughoutthe vertical canopy profile. Measurements were made to obtain parameters from leaves adjacent to the radiation sensors: maximum carboxylation and electron transfer capacity (Va, Ja, ~S^~mol m-2 s-1), day respiration (Rda, ~S^~mol m-2 s-1), leaf nitrogen concentration (Nm, mg g-1) and leaf mass per unit area (La, g m-2). Relative to upper-canopy values, Va declined linearly in 1 : 1 proportion with Na. Relative Va also declined linearly with relative Q, but with a significant intercept at zero irradiance (P < 0.01). This intercept was strongly related to La of the lowest leaves in each canopy (P < 0.01, rr = 0.98, n = 5). For each canopy, daily ln Q was also linearly related with ln Va (P < 0.05), and the intercept was correlated with the value for photosynthetic capacity per unit nitrogen (PUN: Va/Na, ~S^~mol g-1s-1) of the lowest leaves in each canopy (P < 0.05). Va was linearly related with La and Na (P < 0.01), but the slope of the Va : Na relationship varied widely among sites. Hence, whilst there was a unique Va : Na ratio in each stand, acclimation in Va to Q varied predictably with La of the lowest leaves in each canopy. The specific leaf area, Lm (cmr g-1), of the canopy-bottom foliage was also found to predict carboxylation capacity (expressed on a mass basis; Vm, ~S^~mol g-1 s-1) at all sites (P < 0.01). These results invalidate the hypothesis of full acclimation to irradiance, but suggest that La and Lm of the most light-limited leaves in a canopy are widely applicable indicators of the distribution of photosynthetic capacity with height in forests.
    Potentials of anaerobic (pre-)treatment for the cost-effective reclamation of domestic wastewater in irrigated agriculture
    Lier, J.B. van; Zeeman, G. ; Huibers, F.P. - \ 2002
    In: Regional symposium on water recycling in Mediterranean region, Iraklio, 26-20 Sept. 2002 / Angelakis, A.N., Tsagarakis, K.P., Paranychianakis, N.V., Asano, T., Iraklio : National Foundation for Agricultural Research - p. 97 - 104.
    afvalwater - hergebruik van water - irrigatie - tropen - watervoorziening - waterzuivering - waste water - water reuse - water supply - irrigation - tropics - water treatment
    Reuse of treated sewage in irrigated agriculture. Concepts for collection, transport and treatment of domestic wastewater
    Should phosphorus availability be constraining moist tropical forest responses to increasing CO2 concentrations?
    Lloyd, J. ; Bird, M.I. ; Veenendaal, E.M. ; Kruijt, B. - \ 2001
    In: Global biogeochemical cycles in the climate system. San Diego CA (USA) etc. Academic Press, 2001 / Schulze, E.D., Heimann, M., Harrison, S., Holland, E., Lloyd, J., Prentice, I.C., Schimel, D., - p. 95 - 114.
    bodemchemie - fosforkringloop - klimaatverandering - koolstofkringloop - nutriënten - regenwoud - tropen
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