Efficiency of insect-proof net tunnels in reducing virus-related seed degeneration in sweet potato
Ogero, K.O. ; Kreuze, J.F. ; McEwan, M.A. ; Luambano, N.D. ; Bachwenkizi, H. ; Garrett, K.A. ; Andersen, K.F. ; Thomas-Sharma, S. ; Vlugt, R.A.A. van der - \ 2019
Plant Pathology 68 (2019)8. - ISSN 0032-0862 - p. 1472 - 1480.
farmer-multiplier - modelling - net tunnels - seed - sweet potato - virus-related degeneration
Virus-related degeneration constrains production of quality sweet potato seed, especially under open field conditions. Once in the open, virus-indexed seed is prone to virus infection leading to decline in performance. Insect-proof net tunnels have been proven to reduce virus infection under researcher management. However, their effectiveness under farmer-multiplier management is not known. This study investigated the ability of net tunnels to reduce degeneration in sweet potato under farmer-multiplier management. Infection and degeneration were assessed for two cultivars, Kabode and Polista, grown in net tunnels and open fields at two sites with varying virus pressures. There was zero virus incidence at both sites during the first five generations. Sweet potato feathery mottle virus and sweet potato chlorotic stunt virus were present in the last three generations, occurring singly or in combination to form sweet potato virus disease. Virus infection increased successively, with higher incidences recorded at the high virus pressure site. Seed degeneration modelling illustrated that for both varieties, degeneration was reduced by the maintenance of vines under net tunnel conditions. The time series of likely degeneration based on a generic model of yield loss suggested that, under the conditions experienced during the experimental period, infection and losses within the net tunnels would be limited. By comparison, in the open field most of the yield could be lost after a small number of generations without the input of seed with lower disease incidence. Adopting the technology at the farmer-multiplier level can increase availability of clean seed, particularly in high virus pressure areas.
A Systematic Parameter Study on Film Freeze Concentration
Vuist, Jan Eise ; Schutyser, Maarten ; Boom, Remko - \ 2019
In: 29th European Symposium on Computer Aided Process Engineering. - Elsevier B.V. (Computer Aided Chemical Engineering ) - ISBN 9780128186343 - p. 1501 - 1506.
freeze concentration - modelling - solute inclusion
Film freeze concentration is an alternative method to concentrate aqueous streams compared to suspension freeze concentration. Major advantage is that the equipment is less complex and thus capital costs are in principle lower. In our research we investigated especially how hydrodynamics, applied freezing temperatures and solution properties influence inclusion of solutes in ice and ice yield during film freeze concentration. For this we carried out both lab-scale experiments and CFD simulations. Model solutions of sucrose and maltodextrin were concentrated in a stirred vessel by growth of an ice layer at the bottom freezing plate. For varying stirring speeds, feed concentrations and freezing plate temperature profiles we determined the solute inclusion in the grown ice and the ice yield. When increasing stirrer speeds a decreasing amount of solute included in ice was found at constant freezing plate temperature. This can be explained because the transport of the solute molecules in the boundary layer is diffusion limited. An increase in shear above the surface reduces the thickness of this layer and therefore less solute is included in ice at high shear rates. CFD simulations were carried out to describe the hydrodynamics near the surface and to relate the shear rate to the impeller Reynolds number. Moreover, the CFD simulations could explain the increased solute inclusions for higher concentrations of sucrose as higher viscosities lead to significant reduction of shear rates close to the ice layer. The CFD simulations will facilitate easier translation of the obtained results for a differently designed film freeze concentration system. Sucrose and maltodextrin appeared to behave very similar with respect to inclusion behaviour, which may be explained from their similar diffusivities. Ice growth rate is found another important factor and is very much influence by applied freezing temperatures. Our experiments showed that there is a critical ice growth rate. If this ice growth rate is exceeded more solutes will be included in the ice layer. In this case the solute molecules will not have the chance to move away from the ice boundary. The next step in our research is modelling of the ice growth rate as function of the freezing plate temperature to optimise both ice yield and solute inclusion.
The social construction and consequences of groundwater modelling : insight from the Mancha Oriental aquifer, Spain
Sanz, David ; Vos, Jeroen ; Rambags, Femke ; Hoogesteger, Jaime ; Cassiraga, Eduardo ; Gómez-Alday, Juan José - \ 2019
International Journal of Water Resources Development 35 (2019)5. - ISSN 0790-0627 - p. 808 - 829.
Groundwater governance - model-based policy-making - modelling - Social Construction of Technology (SCOT) - Spain
Groundwater flow models have been increasingly used to support policy making. A substantial amount of research has been dedicated to improving, validating and calibrating models and including stakeholders in the modelling process. However, little research has been done to analyze how the choices of model makers and steering by policy makers result in models with specific characteristics, which only allow specific modelling outcomes, and how the use of these modelling outcomes leads to specific social, economic and environmental consequences. In this study, we use the social construction of technology framework to explore the development, characteristics and uses of the groundwater model of the Mancha Oriental aquifer in Spain. The specific characteristics and functioning of this model influenced the policy implementation, implying that involving stakeholders in the development and use of models is crucial for improved democratic policy making.
Quantitative analysis of the dose–response of white spot syndrome virus in shrimp
Ngo, Thuy T.N. ; Senior, Alistair M. ; Culina, Antica ; Santos, Eduardo S.A. ; Vlak, Just M. ; Zwart, Mark P. - \ 2018
Journal of Fish Diseases 41 (2018)11. - ISSN 0140-7775 - p. 1733 - 1744.
dose–response - infection - meta-analysis - modelling - shrimp - white spot syndrome virus
White spot syndrome virus (WSSV) is an important cause of mortality and economic losses in shrimp farming. Although WSSV-induced mortality is virus dose dependent and WSSV infection does not necessarily lead to mortality, the relationships between virus-particle dose, infection and mortality have not been analysed quantitatively. Here, we explored WSSV dose–response by a combination of experiments, modelling and meta-analysis. We performed dose–response experiments in Penaeus vannamei postlarvae, recorded host mortality and detected WSSV infection. When we fitted infection models to these data, two models—differing in whether they incorporated heterogeneous host susceptibility to the virus or not—were supported for two independent experiments. To determine the generality of these results, we reanalysed published data sets and then performed a meta-analysis. We found that WSSV dose–response kinetics is indeed variable over experiments. We could not clearly identify which specific infection model has the most support by meta-analysis, but we argue that these results also are most concordant with a model incorporating varying levels of heterogeneous host susceptibility to WSSV. We have identified suitable models for analysing WSSV dose–response, which can elucidate the most basic virus–host interactions and help to avoid underestimating WSSV infection at low virus doses.
What is the role of the model in socio-hydrology? Discussion of “Prediction in a socio-hydrological world”*
Melsen, Lieke Anna ; Vos, Jeroen ; Boelens, Rutgerd - \ 2018
Hydrological Sciences Journal 63 (2018)9. - ISSN 0262-6667 - p. 1435 - 1443.
modelling - prediction - socio-hydrology - socio-natural relationships - transdisciplinarity
Srinivasan et al. provide an interesting overview of the challenges for long-term socio-hydrological predictions. Although agreeing with most of the statements made, we argue for the need to take socio-hydrological analysis a step further and add some fundamental considerations, especially concerning the crucial importance of many (conscious and unconscious) assumptions made upfront of the modelling exercise. Eventual assumptions of technological determinism need correction: Models are not “value-free”, but uncertain, subjective and a product of the society in which they were shaped. It is important to acknowledge this uncertainty and bias when making decisions based on socio-hydrological models, considering also that these models are “social and political actors” in and by themselves. Furthermore, socio-hydrological models require a transdisciplinary approach, since physical water availability is only one of the boundary conditions for society. Last but not least, interaction with stakeholders remains important to enable understanding of what the variable of interest is.
Integrated Adaptation Tipping Points (IATPs) for urban flood resilience
Ahmed, Farhana ; Khan, M.S.A. ; Warner, Jeroen ; Moors, Eddy ; Terwisscha van Scheltinga, Catharien - \ 2018
Environment and Urbanization 30 (2018)2. - ISSN 0956-2478 - p. 575 - 596.
Adaptation Tipping Point - Dhaka - flood risk management - modelling - resilience - social tipping point
This paper applies an Adaptation Tipping Point (ATP) approach for the assessment of vulnerability to flooding in the city of Dhaka, Bangladesh. A series of rigorous modelling exercises for fluvial and pluvial flooding was conducted to identify the critical ATPs of the physical system, under both existing and proposed flood risk management strategies, for different urban and climate change scenarios. But a standalone assessment of the physical system’s ATPs is insufficient to gain a complete understanding of flood risks; community resilience also depends on people’s adaptability and the acceptance of risks by the community in question. Through participatory public consultations, this study determines the critical ATPs for community risk acceptance. The concept of the “Integrated Adaptation Tipping Point (IATP)”, introduced here, combines the accepted level of risk to the community with the ATPs for physical systems. This approach reveals that the assessed vulnerability to flooding increases when social tipping points are considered.
How to analyse urban resource cycles : a dynamic systems approach to facilitate decision-making
Bozileva, Elvira ; Leusbrock, Ingo ; Cappon, Hans J. ; Rijnaarts, Huub H. ; Keesman, Karel J. - \ 2018
IFAC-PapersOnLine 51 (2018)2. - ISSN 2405-8963 - p. 541 - 546.
decision support - modelling - optimisation - sensitivity analysis - urban resources
Individual technologies allowing and enabling sustainable resource management in urban areas are available on the market. Modelling and analysis tools to aid in tailoring these technologies for a specific context are abundant as well. However, compartmentalization of scientific knowledge does not allow researchers and practitioners to take full advantage of the available information and work towards the common goal of sustainability. The aim of this paper is to present a methodology, which can support researchers, engineers and planners who intend to use a modelling approach to tailor the technological solutions for a specific urban system. The methodology encompasses a systematic inventory of tools and techniques that can be used at different stages of model-based decision-making, such as objective formulation, model development, sensitivity analysis and optimisation. Whereas the methodology is intended to be generic, its applicability is illustrated with an example related to a residential water-energy cycle.
Estimating winter survival of winter wheat by simulations of plant frost tolerance
Bergjord Olsen, A.K. ; Persson, T. ; Wit, A. de; Nkurunziza, L. ; Sindhøj, E. ; Eckersten, H. - \ 2018
Journal of Agronomy and Crop Science 204 (2018)1. - ISSN 0931-2250 - p. 62 - 73.
FROSTOL - LT - modelling - plant cover - risk assessments - winter damage
Based on soil temperature, snow depth and the grown cultivar's maximum attainable level of frost tolerance (LT50c), the FROSTOL model simulates development of frost tolerance (LT50) and winter damage, thereby enabling risk calculations for winter wheat survival. To explore the accuracy of this model, four winter wheat cultivars were sown in a field experiment in Uppsala, Sweden in 2013 and 2014. The LT50 was determined by tests of frost tolerance in November, and the cultivars’ LT50c was estimated. Further, recorded winter survival from 20 winter wheat field variety trials in Sweden and Norway was collected from two winter seasons with substantial winter damages. FROSTOL simulations were run for selected cultivars at each location. According to percentage of winter damage, the cultivar survival was classified as “survived,” “intermediate” or “killed.” Mean correspondence between recorded and simulated class of winter survival was 75% and 37% for the locations in Sweden and Norway, respectively. Stress factors that were not accounted for in FROSTOL might explain the poorer accuracy at the Norwegian locations. The accuracy was poorest for cultivars with intermediate LT50c levels. When low temperature was the main cause of damage, as at the Swedish locations, the model accuracy was satisfying.
Estimating the economic impact of subclinical ketosis in dairy cattle using a dynamic stochastic simulation model
Mostert, P.F. ; Bokkers, E.A.M. ; Middelaar, C.E. van; Hogeveen, H. ; Boer, I.J.M. de - \ 2018
Animal 12 (2018)1. - ISSN 1751-7311 - p. 145 - 154.
cost - dairy cow - disease - modelling - parity
The objective of this study was to estimate the economic impact of subclinical ketosis (SCK) in dairy cows. This metabolic disorder occurs in the period around calving and is associated with an increased risk of other diseases. Therefore, SCK affects farm productivity and profitability. Estimating the economic impact of SCK may make farmers more aware of this problem, and can improve their decision-making regarding interventions to reduce SCK. We developed a dynamic stochastic simulation model that enables estimating the economic impact of SCK and related diseases (i.e. mastitis, metritis, displaced abomasum, lameness and clinical ketosis) occurring during the first 30 days after calving. This model, which was applied to a typical Dutch dairy herd, groups cows according to their parity (1 to 5+), and simulates the dynamics of SCK and related diseases, and milk production per cow during one lactation. The economic impact of SCK and related diseases resulted from a reduced milk production, discarded milk, treatment costs, costs from a prolonged calving interval and removal (culling or dying) of cows. The total costs of SCK were €130 per case per year, with a range between €39 and €348 (5 to 95 percentiles). The total costs of SCK per case per year, moreover, increased from €83 per year in parity 1 to €175 in parity 3. Most cows with SCK, however, had SCK only (61%), and costs were €58 per case per year. Total costs of SCK per case per year resulted for 36% from a prolonged calving interval, 24% from reduced milk production, 19% from treatment, 14% from discarded milk and 6% from removal. Results of the sensitivity analysis showed that the disease incidence, removal risk, relations of SCK with other diseases and prices of milk resulted in a high variation of costs of SCK. The costs of SCK, therefore, might differ per farm because of farm-specific circumstances. Improving data collection on the incidence of SCK and related diseases, and on consequences of diseases can further improve economic estimations.
Measuring and modelling water transport on Skaftafellsheioi, Iceland
Dijksma, R. ; Avis, Lisette - \ 2017
Forum Geografic 15 (2017)suppl.. - ISSN 1583-1523 - p. 66 - 72.
Basalt aquifers - MODFLOW - modelling - Representative Elementary Volume
Areas with thick basaltic aquifers are used for drinking water supply and irrigation purposes, such as the Columbia River Basalt group in northwest USA and the Deccan Traps in India. However, rainfall-runoff processes in these basaltic areas are poorly understood. Cooling joints can transport large amounts of water, but – due to their limited porosity – they are vulnerable for over-abstraction. On Iceland, in the small Skaftafellsheiði basaltic catchment (4 x 6 km), field data were collected in 2014 and 2015. Two small streams discharge the rain surplus. Precipitation was measured at various elevations on the ridge. Also, the discharge of the streams was measured. A groundwater flow model was constructed in order to get more insight in the physical properties of the basalt aquifer and its rainfall-runoff properties. The field experiments showed that precipitation increases linearly with surface elevation. On average, the precipitation at 800 m+msl was almost double, relative to the precipitation at 200 m+msl. Calculated ETpot was rather high, due to the 19 potential sun hours per day during the Icelandic summer. Field experiments revealed quick discharge response on rainfall events, but also rather constant base flow during dryer periods. This indicates a limited infiltration capacity, but also a considerable storage capacity in the subsequent layers. The peat layer is believed to be the dominant storage/reservoir. Peat, regolith and an organic layer formed the top layer in the GMS-Modflow groundwater model. The thick basaltic aquifer was split in a series of model layers. Best results were obtained by using a decreasing hydraulic conductivity to depth. The transient model overestimated the groundwater levels at the outlet, but managed to reproduce the wet/dry conditions in the catchment rather well. This indicates that it is possible to model complex basaltic aquifers, by taking a large Representative Elementary Volume (REV) as starting point
Efficiency of phosphorus resource use in Africa as defined by soil chemistry and the impact on crop production
Magnone, Daniel ; Bouwman, Alexander F. ; Zee, Sjoerd E.A.T.M. Van Der; Sattari, Sheida Z. ; Beusen, Arthur H.W. ; Niasar, Vahid J. - \ 2017
Energy Procedia 123 (2017). - ISSN 1876-6102 - p. 97 - 104.
DPPS - modelling - phosphorus - soil - soil resources
By 2050 the global population will be 9.7 billion, placing an unprecedented burden on the world's soils to produce extremely high food yields. Phosphorus (P) is crucial to plant growth and mineral fertilizer is added to soil to maintain P concentrations, however this is a finite resource, thus efficient use is critical. Plants primarily uptake P from a labile (available) P pool and not from the stable solid phase; transfer between these pools limits bioavailability. Transfer is controlled by soil properties which vary between soil types. The dynamic phosphorus pool simulator (DPPS) quantifies crop production and soil P relationships by utilising the transfer. This approach effectively models crop uptake from soil inputs, but it does not quantify the efficiency use. This study incorporates geochemical techniques within DPPS to quantify the efficiency of fertilizer-P use based on soil chemistry.
Shifts of community composition and population density substantially affect ecosystem function despite invariant richness
Spaak, Jurg W. ; Baert, Jan M. ; Baird, Donald J. ; Eisenhauer, Nico ; Maltby, Lorraine ; Pomati, Francesco ; Radchuk, Viktoriia ; Rohr, Jason R. ; Brink, Paul J. van den; Laender, Frederik De - \ 2017
Ecology Letters 20 (2017)10. - ISSN 1461-023X - p. 1315 - 1324.
Algae - biodiversity - coexistence - community ecology - modelling - primary production
There has been considerable focus on the impacts of environmental change on ecosystem function arising from changes in species richness. However, environmental change may affect ecosystem function without affecting richness, most notably by affecting population densities and community composition. Using a theoretical model, we find that, despite invariant richness, (1) small environmental effects may already lead to a collapse of function; (2) competitive strength may be a less important determinant of ecosystem function change than the selectivity of the environmental change driver and (3) effects on ecosystem function increase when effects on composition are larger. We also present a complementary statistical analysis of 13 data sets of phytoplankton and periphyton communities exposed to chemical stressors and show that effects on primary production under invariant richness ranged from −75% to +10%. We conclude that environmental protection goals relying on measures of richness could underestimate ecological impacts of environmental change.
Empirical model for mineralisation of manure nitrogen in soil
Sørensen, Peter ; Thomsen, Ingrid K. ; Schroder, Jaap - \ 2017
Soil Research 55 (2017)5-6. - ISSN 1838-675X - p. 500 - 505.
cattle slurry - immobilisation - modelling - organic N - pig slurry
A simple empirical model was developed for estimation of net mineralisation of pig and cattle slurry nitrogen (N) in arable soils under cool and moist climate conditions during the initial 5 years after spring application. The model is based on a Danish 3-year field experiment with measurements of N uptake in spring barley and ryegrass catch crops, supplemented with data from the literature on the temporal release of organic residues in soil. The model estimates a faster mineralisation rate for organic N in pig slurry compared with cattle slurry, and the description includes an initial N immobilisation phase for both manure types. The model estimates a cumulated net mineralisation of 71% and 51% of organic N in pig and cattle slurry respectively after 5 years. These estimates are in accordance with some other mineralisation studies and studies of the effects of manure residual N in other North European countries.
Development and validation of a drinking water temperature model in domestic drinking water supply systems
Zlatanovic, Ljiljana ; Moerman, Andreas ; Hoek, Jan Peter van der; Vreeburg, Jan ; Blokker, Mirjam - \ 2017
Urban Water Journal 14 (2017)10. - ISSN 1573-062X - p. 1031 - 1037.
domestic systems - Drinking water - modelling - water temperature
Domestic drinking water supply systems (DDWSs) are the final step in the delivery of drinking water to consumers. Temperature is one of the rate-controlling parameters for many chemical and microbiological processes and is, therefore, considered as a surrogate parameter for water quality processes. In this study, a mathematical model is presented that predicts temperature dynamics of the drinking water in DDWSs. A full-scale DDWS resembling a conventional system was built and run according to one year of stochastic demands with a time step of 10 s. The drinking water temperature was measured at each point-of-use in the systems and the data-set was used for model validation. The temperature model adequately reproduced the temperature profiles, both in cold and hot water lines, in the full-scale DDWS. The model showed that inlet water temperature and ambient temperature have a large effect on the water temperature in the DDWSs.
A methodical approach for the assessment of waste sorting plants
Feil, Alexander ; Pretz, Thomas ; Vitz, Philipp ; Thoden van Velzen, Ulphard - \ 2017
Waste Management and Research 35 (2017)2. - ISSN 0734-242X - p. 147 - 154.
assessment - back-calculation - beverage cartons - decision tree - modelling - sample taking options - separation coefficient - Waste sorting plants - yield
A techno-economical evaluation of the processing result of waste sorting plants should at least provide a realistic assessment of the recovery yields of valuable materials and of the qualities of the obtained products. This practical data is generated by weighing all the output products and sampling these products. Due to the technological complexity of sorting plants, for example, lightweight packaging waste treatments plants and the high expenditures concerning time and costs of sampling with subsequent manual sorting for quality determination, usually only final products undergo such an investigation. Thereby, the transferability of the results depends decisively on the boundary conditions (extent, throughput of the plant, process parameterization). Given that the process is too complex, not all relevant information of the process steps can be determined by sampling. By model calculations and/or adjustment of reasonable assumptions, information concerning weak points in the process can be identified, which can be used for further plant optimization. For the example of the recovery of beverage cartons from co-collected and mechanically recovered mixtures of lightweight packaging waste, a methodical approach for the assessment of processing results will be presented.
Modelling the colour of strawberry spread during storage, including effects of technical variations
Kadivec, Mirta ; Tijskens, Pol ; Kopjar, Mirela ; Simčič, Marjan ; Požrl, Tomaž - \ 2016
Polish Journal of Food and Nutrition Sciences 66 (2016)4. - ISSN 1230-0322 - p. 271 - 276.
colour - modelling - strawberry spread - technical variation
The colour of freshly processed strawberry spread changes relatively rapidly from a bright red to a dull red, which then makes its appearance generally less acceptable for consumers. The colours of strawberry spreads following several processing conditions were measured under different storage conditions. Additional sugar and colorant had only slight effects on the colour decay, while exclusion of oxygen and daylight did not affect this process. The only condition that clearly maintained the freshly processed appearance was storage at 4°C. Hexagonal bottles were filled with the strawberry spreads and their colour was repeatedly measured at the six sides of the bottles, using a Minolta chroma meter. Data were analysed using non-linear indexed regression analysis based on a logistic function for the three colour aspect of a∗, b∗ and L∗. This technology allowed the determination of the variation in these data in terms of improved reliability (R2 adj, >90%). It also allowed better interpretation of the processes involved. All variations in the data could be attributed to technical variation.
Temperature response of bundle-sheath conductance in maize leaves
Yin, Xinyou ; Putten, Peter E.L. Van Der; Struik, Paul C. ; Driever, Steven M. - \ 2016
Journal of Experimental Botany 67 (2016)9. - ISSN 0022-0957 - p. 2699 - 2714.
Diffusive resistance - maximum PEPc activity - maximum Rubisco activity - modelling - warming effect - Zea mays
A small bundle-sheath conductance (g bs) is essential for the C4 CO2-concentrating mechanism to suppress photorespiration effectively. To predict the productivity of C4 crops accurately under global warming, it is necessary to examine whether and how g bs responds to temperature. We investigated the temperature response of g bs in maize by fitting a C4 photosynthesis model to combined gas exchange and chlorophyll fluorescence measurements of irradiance and CO2 response curves at 21% and 2% O2 within the range of 13.5-39 °C. The analysis was based on reported kinetic constants of C4 Rubisco and phosphoenolpyruvate carboxylase and temperature responses of C3 mesophyll conductance (g m). The estimates of g bs varied greatly with leaf temperature. The temperature response of g bs was well described by the peaked Arrhenius equation, with the optimum temperature being ~34 °C. The assumed temperature responses of g m had only a slight impact on the temperature response of g bs. In contrast, using extreme values of some enzyme kinetic constants changed the shape of the response, from the peaked optimum response to the non-peaked Arrhenius pattern. Further studies are needed to confirm such an Arrhenius response pattern from independent measurement techniques and to assess whether it is common across C4 species.
Plant uptake of cadmium as affected by variation in sorption parameters.
Boekhold, A.E. ; Zee, S.E.A.T.M. van der - \ 1990
In: Plant nutrition : physiology and applications : proceedings of the eleventh international plant nutrition colloquium, 30 July - 4 August 1989, Wageningen, The Netherlands / van Beusichem, M.L., Dordrecht : Kluwer - ISBN 9780792307402 - p. 313 - 316.
cadmium - crop quality - heavy metals - modelling - soil heterogeneity
The effect of accumulation of cadmium in the topsoil on cadmium contents in crops is evaluated for field scale situations, using a model that links cadmium input, plant uptake, and leaching to cadmium accumulation in the rootzone. Measurements of pH and organic matter content, which regulate sorption behaviour to a large extent, show significant field-scale variability. Taking this heterogeneity into account, the probability that the cadmium concentration in part of the plants exceeds quality standards is compared with exceedance of the distribution average.