Dynamic Conceptual Model Research Articles

A simulation model for studying the implementation of performance-based fire safety design in buildings

A large volume of huge and complex buildings are being constructed in many cities, especially in the Far East Asia, The conventional regulatory control of building design on the basis of prescriptive building and fire safety codes and regulations may not facilitate the building designers to compile an innovative design. In particular, fire safety codes and regulations are noted to be rigid and have significant influence on the design of building layout and structures. The introduction of a performance-based approach, in which buildings are designed to meet the performance requirements rather than strictly complying with the prescribed rules, recently provides the opportunity for building designers to generate unique and daring solutions. To examine the effect of introducing such performance approach in the regulatory system, a conceptual system dynamic model has been established, with reference to the Hong Kong building control system, to explore the behavior and changes of the system. The model is conceptualized around the technical and mental factors that impact on the decisions of building control officials and various issues. To build the system dynamics model, a causal diagram showing the interrelationships of the system components is first established. It can assist the identification of attributes that affect the implementation and the performance of building design control policy. On the basis of the causal diagram, a simulation model is formulated. Some issues that may affect the implementation of performance-based fire safety design can be examined and discussed.

Seasonal flooding, instream habitat structure and fish assemblages in the Mulgrave River, north-east Queensland: towards a new conceptual framework for understanding fish-habitat dynamics in small tropical rivers

Strong relationships between seasonal flooding, instream habitat structure and fish assemblages have been well documented in large tropical rivers (e.g. the flood pulse concept). However, the mechanics of these relationships are likely to differ substantially in smaller coastal rivers, such as those in Costa Rica, south-east Brazil and Australia’s Wet Tropics. These systems typically feature steep upland streams with short, deeply incised lowland channels and poorly connected floodplains. This hypothesis was investigated by documenting spatial and temporal variation in fish-habitat relationships in the Mulgrave River, north-east Queensland. Sampling was conducted at four lowland sites under a range of flow conditions, from dry-season baseflows to a one-in-ten-year flood. Longitudinal environmental gradients and fine-scale habitat patches were important in regulating fish assemblage structure during the dry season. However, high wet-season flows, constrained by the deep channel, acted as disturbances rather than gentle flood-pulses. In particular, the mobilisation of bed sediments led to scouring of aquatic vegetation and a dramatic reduction in habitat heterogeneity. Seasonal movements of fish led to significant changes in assemblage structure – from a community dominated by Neosilurus ater, Hypseleotris compressa, Awaous acritosus and Redigobius bikolanus during the dry season, to one dominated by Nematalosa erebi, Ambassis agrammus and Glossamia aprion during the wet season. Based on these observations, together with information from the literature, a conceptual model of fish-habitat dynamics is presented that is better suited to small tropical rivers than those developed in larger systems with expansive floodplains.

Geomorphology of upland peat: erosion, form and landscape change

Series Editors' Preface. Acknowledgements. 1. Introduction. 1.1 The aims of this volume. 1.1.1 Thematic coverage. 1.1.2 Geographical context. 1.2 Terminology, definitions and peatland geomorphology. 1.2.1 Definitions of Peat. 1.2.2 The Physical and geotechnical properties of peat. 1.2.3 Peatland classification. 1.3 The geography of blanket mire complexes. 1.4 Patterns of peat erosion in space and time. 1.4.1 The onset of peat erosion. 1.4.2 Direct observation of the onset of erosion. 1.5 Causes of peat erosion. 1.6 A brief history of the evolution of peatland geomorphology. 1.6.1 Accounts of erosion in the natural science tradition. 1.6.2 Descriptive accounts of widespread peat erosion. 1.6.3 Quantitative observations of blanket peatlands. 1.7 Structure of this volume and the peat land system model. 2. The Hydrology of Upland Peatlands. 2.1 Introduction. 2.2. Controls on water movement in peatland systems. 2.2.1 Hydraulic conductivity of upland peat soils. 2.2.2 The diplotelmic mire hypothesis. 2.2.3 Groundwater flow in upland peatlands. 2.2.4 Evaporation. 2.2.5 Runoff generation. 2.2.6 The Water balance of ombrotrophic mires. 2.3 Geomorphology and the hydrology of upland peatlands. 3. Sediment Production. 3.1 Introduction. 3.1.1 Monitoring sediment production using erosion pins. 3.1.2 Sediment trap data. 3.2 Sediment production as a control on catchment sediment flux. 3.3 Evidence from field observation. 3.3.1 Climate correlations with trap data. 3.3.2 Direct observations of surface change. 3.4 Evidence from controlled experiments. 3.5 Timescales of sediment supply. 3.6 Conclusion. 4. Fluvial Processes and Peat Erosion. 4.1 Introduction. 4.2 Gully erosion of blanket peat. 4.2.1 Gully morphology and topology. 4.2.2 Processes of Gully erosion. 4.3 Erosion and transport of peat in perennial stream channels. 4.3.1 Production of peat blocks by fluvial erosion. 4.3.2 Transport of peat blocks in stream channels. 4.3.3 The fate of fine peat sediment in channel. 4.4 Sediment yield. 4.4.1 A conceptual model of sediment dynamics in eroding blanket peatlands. 4.4.2 Sediment yield, sediment supply and assessing catchment erosion status. 4.5 Conclusions. 5. Slope Processes and Mass Movements. 5.1 Introduction. 5.2 Peat covered hillslopes. 5.2.1 Limits to the stability of peat on slopes. 5.2.2 Creep on peat hillslopes. 5.3 Morphology of rapid peat mass movements. 5.3.1 Source zone. 5.3.2 Rafted peat debris. 5.3.3 Runout track. 5.3.4 Secondary tension and compression features. 5.3.5 Bog burst and peat slides - are they different?. 5.4 Mechanism of peat failure. 5.4.1 Speed of failure and movement. 5.5 Significance of surface hydrology in peat failures. 5.5.1 Water content and pore pressures. 5.5.2 Rainfall. 5.5.3 Slope drainage. 5.6 Stability analysis and modelling of peat mass movements. 5.7 The changing frequency of peat mass movements over time. 5.8 Summary and overall framework. 6. Wind Erosion Processes. 6.1 Introduction. 6.2 Wind erosion in the uplands and the significance in peatland environments. 6.3 Mechanisms of wind erosion. 6.4 The significance of wet or dry wind erosion processes. 6.5 Direct measurements of wind erosion of peat. 6.6 Aeolian landforms. 6.7 The significance of wind erosion for landscape development in upland peatlands. 6.8 Conclusions. 6.8.1 Further research - an agenda for pluvio-aeolian studies of upland peat. 7. Peat Erosion Forms - from Landscape to Micro-relief. 7.1 Rationale and introduction. 7.2 Macroscale - Region / Catchment Scale. 7.3 Mesoscale - Slope-Catena Scale. 7.4 Microscale - material structure scale. 7.5 Linking the geomorphological and the ecohydrological. 7.6 Conclusions. 8. Sediment Dynamics, Vegetation, and Landscape Change. 8.1 Introduction. 8.2 The effect of peatland dynamics on long term sediment budgets. 8.3 Mass balance evidence of patterns of long term erosion. 8.4 Re-vegetation of eroding peatlands. 8.4.1 Artificial re-vegetation of bare peat surfaces. 8.4.2 Natural revegetation of eroded landscapes. 8.5 Controls and mechanisms of natural re-vegetation. 8.5.1 Extrinsic controls on re-vegetation. 8.5.2 Intrinsic controls on re-vegetation. 8.5.3 Eriophorum spp. as Keystone Species for Re-vegetation of Eroded Peatlands. 8.5.4 Geomorphology, ecology, and 'erosion-regeneration complexes'. 8.5.5 Re-vegetation dynamics and long term patterns of erosion. 8.6 Stratigraphic evidence of erosion and re-vegetation. 8.7 The future of blanket peat sediment systems. 8.8 Changes in pollution climate. 8.9 Climate change impacts. 8.9.1 Increased summer drought. 8.9.2 Increased summer and winter storminess. 8.9.3 Changes in the growing season and vegetation. 8.9.4 Overall response of the peat land system. 8.10 Relative importance of peat erosion in wider upland sediment budgets. 8.11 Conclusions. 9. Implications and Conclusions. 9.1 Implications of widespread peat erosion. 9.2 Upland peatland erosion and carbon budgets. 9.2.1 Case Study Example: the Rough Sike sediment-carbon budget. 9.3 Release of stored contaminants from eroding peatlands. 9.4 Restoration of eroded upland peatlands. 9.4.1 Frameworks for restoration. 9.4.2 Approaches to restoration. 9.4.3 Implications of the landsystems model and sediment budget work for restoration. 9.5 Conclusions. 9.5.1 The nature of upland peatlands. 9.5.2 Geomorphological processes in upland peatlands. 9.5.3 The future of upland peatlands. 9.5.4 Representativeness of the peat land system model. Index.

A dynamic model of customer complaining behaviour from the perspective of service‐dominant logic

PurposeThe purpose of this paper is to propose a conceptual model of customer complaining behaviour as a dynamic process in accordance with the service‐dominant logic perspective of marketing.Design/methodology/approachThe study reviews the common behaviour models of customer complaints and relates this to the service‐dominant logic perspective in order to develop and describe a dynamic conceptual model of customer complaining behaviour.FindingsThe proposed model posits three categories of complaining behaviour due to a customer's unfavourable service experience: no complaining response, communication complaining responses, and action complaining responses.Research limitations/implicationsEmpirical validation of the proposed conceptual model is needed.Practical implicationsThe proposed model can be used by managers to understand the various behaviour responses of customer complaints that the company experiences. In addition, the model assists in framing appropriate managerial responses, including service recovery and improved service design.Originality/valueThe study represents a thorough conceptual examination of the complaint process and proposes a dynamic model of customer complaining behaviour based on the service‐dominant logic perspective.

How uncertain is model-based prediction of copper loads in stormwater runoff?

In this paper, we conduct a systematic analysis of the uncertainty related with estimating the total load of pollution (copper) from a separate stormwater drainage system, conditioned on a specific combination of input data, a dynamic conceptual pollutant accumulation-washout model and measurements (runoff volumes and pollutant masses). We use the generalized likelihood uncertainty estimation (GLUE) methodology and generate posterior parameter distributions that result in model outputs encompassing a significant number of the highly variable measurements. Given the applied pollution accumulation-washout model and a total of 57 measurements during one month, the total predicted copper masses can be predicted within a range of +/-50% of the median value. The message is that this relatively large uncertainty should be acknowledged in connection with posting statements about micropollutant loads as estimated from dynamic models, even when calibrated with on-site concentration data.

The lightning–biota climatic feedback

AbstractWe investigate a negative climatic feedback which involves an increase in deposition of lightning‐produced nitrogen compounds into ecosystems as a response to a global temperature rise. This increases primary production on both land and ocean, which reduces atmospheric carbon dioxide (CO2), and consequently global temperature in return. Large uncertainties in numerous processes and parameters in this feedback exist and therefore its importance is unclear. This feedback is investigated using a conceptual dynamical model, including assessing its role in counteracting anthropogenic‐induced warming by reducing the rate of accumulation and concentration of atmospheric CO2. Overall, this study suggests that this feedback is of mild strength in the climate system, but raises the intriguing possibility that it should be considered in long‐term climate simulations. Further work in investigating this climatic feedback is required.

A dynamic conceptual model of care planning

This article presents a conceptual model of the care planning process developed to identify the hypothetical links between structural, process and outcome factors important to the quality of the process. Based on existing literature, it was hypothesized that a thorough assessment of patients' health needs is an important prerequisite when making a rigorous diagnosis and preparing plans for various care interventions. Other important variables that are assumed to influence the quality of the process are the care culture and professional knowledge. The conceptual model was developed as a system dynamics causal loop diagram as a first essential step towards a computed model. System dynamics offers the potential to describe processes in a nonlinear, dynamic way and is suitable for exploring, comprehending, learning and communicating complex ideas about care processes.

A DELICATE BALANCE: ECOHYDROLOGICAL FEEDBACKS GOVERNING LANDSCAPE MORPHOLOGY IN A LOTIC PEATLAND

The Everglades ridge and slough landscape is characterized by elevated sawgrass ridges regularly interspersed among lower and more open sloughs that are aligned parallel to the historic flow direction. Landscape degradation, characterized by topographic flattening, has coincided with a century of drainage, levee construction, nutrient enrichment, and flow reductions. Here we develop a conceptual model of Everglades landscape dynamics based on a literature synthesis and supported by the numerical model PeatAccrete. We propose that two feedback mechanisms govern landscape characteristics. The first, simulated with PeatAccrete, involves differential peat accretion governed by water level and phosphorus concentration, leading to the attainment of an equilibrium ridge elevation relative to slough. Differential peat accretion, however, cannot produce a characteristic ridge width or landscape wavelength. Instead, we propose that feedback between channel morphology and sediment mass transfer controls lateral and longitudinal topographic features, consistent with processes in anabranching rivers. This sediment transport feedback was critical in pattern initiation and evolution, and sediment redistribution from slough to ridge provides a plausible mechanism for preventing gradual ridge expansion. However, PeatAccrete model results show that, in the absence of sediment transport, ridges expand only on the order of meters per century. This result suggests that a combination of factors has driven the widespread disappearance of sloughs over the past century, including altered vertical peat accretion rates that lead to slough infilling. Sensitivity tests indicated that changes in duration and depth of surface water inundation, phosphorus supply, and redox potential have altered differential peat accretion rates in a way that favors topographic flattening. These factors are relatively well defined compared with the role of sediment transport, which requires further quantification. Because both positive and negative feedback processes interact in the Everglades, the trajectory of landscape evolution in time will depend upon current conditions, with areas of remnant ridge and slough topography being more likely than areas of degraded topography to respond to changes in water management in ways that enhance landscape heterogeneity over human timescales. Dual feedbacks between peat accretion and sediment transport are likely important controls on landscape evolution in low-gradient peatlands worldwide with pulsed, unidirectional flow.

Entrepreneurial knowledge management and sustainable opportunity creations: a conceptual framework

The aim of this work is to develop a dynamic conceptual model to assess and to assist entrepreneurial knowledge management and sustainable opportunity creations. The conceptual model is backed by a theoretical framework drawing on the Resource-Based View (RBV) of the firm, the knowledge-based view of the firm, and entrepreneurship. The model employs the following elements: tacit and explicit knowledge; and internal, semi-internal and external knowledge reservoirs. Further, gate-keeping and processes concerning the identification of requisite knowledge, the attraction and exploitation of this knowledge, and finally, the mechanisms to protect the firm's knowledge reservoirs, are central elements. The model can be used in different scenarios, explaining and guiding a firm's challenges regarding achieving competitive advantage.

From rhetoric to reality: A systemic approach to understanding the constraints faced by Health For All initiatives in England

The increased appreciation of the effects socio-ecological factors have on health, witnessed over the last few decades, has given rise to many international, national, and local Health For All (HFA) initiatives tasked with addressing them. However, such initiatives have had to operate within environments which were not specifically designed for them or for the new social (rather than medical) perspective on health they were based upon. As a result, they have been facing significant barriers and constraints to fulfilling their mission. This paper explores the constraints which are imposed on such initiatives by the various environments within which they are nested. Drawing upon our experience in evaluating European Healthy City (HC) projects and English Health Action Zones (HAZs), we develop a dynamic conceptual model which shows how the national, governmental policy, interorganisational, organisational, and initiative environments relate with each other and their cumulative effects on initiatives. We argue that this model, and the principles on which it is based, can be used constructively to identify constraints facing HFA-type initiatives in many countries. We use our case study of English HCs and HAZs to illustrate the applicability of the model in a particular national context. We, first, interpret the model to reflect differences and similarities between their respective environments and trace the sources of the different constraints they encountered. We, then, show how an alternative structural configuration could enable some of these constraints to be eliminated. We argue that what is needed for HFA initiatives to be able to fulfill their brief in full is for governments to rethink existing organisational structures and update them to match the evolution of ideas on health which have emerged over the last decades.

Understorey gaps influence regeneration dynamics in subtropical coastal dune forest

Dominant understorey species influence forest dynamics by preventing tree regeneration at the seedling stage. We examined factors driving the spatial distribution of the monocarpic species Isoglossa woodii, a dominant understorey herb in coastal dune forests, and the effect that its cover has on forest regeneration. We used line transects to quantify the area of the forest understorey with I. woodii cover and with gaps in the cover. Paired experimental plots were established in semi-permanent understorey gaps with I. woodii naturally absent and in adjacent areas with I. woodii present to compare plant community composition, soil, and light availability between the two habitats. Isoglossa woodii was widespread, covering 65–95% of the understorey, while gaps covered the remaining 5–35% of the area. The spatial distribution of this species was strongly related to tree canopy structure, with I.␣woodii excluded from sites with dense tree cover. Seedling establishment was inhibited by low light availability (<1% of PAR) beneath I.␣woodii. When present, I. woodii reduced the density and species richness of tree seedlings. The tree seedling community beneath I. woodii represented a subset of the seedling community in gaps. Some species that were found in gaps did not occur beneath I. woodii at all. There were no significant differences between the sapling and canopy tree communities in areas with I. woodii gaps and cover. In the coastal dune forest system, seedling survival under I. woodii is dependent on a species’ shade tolerance, its ability to grow quickly during I. woodii dieback, and/or the capacity to regenerate by re-sprouting and multi-stemming. We propose a general conceptual model of forest regeneration dynamics in which the abundant understorey species, I. woodii, limits local tree seedling establishment and survival but gaps in the understorey maintain tree species diversity on a landscape scale.

SedTrap: A Conceptual Model for Trap Efficiencies in a Sedimentation Basin

Sedimentation basins and sediment traps are established methodologies for reducing sediment and other pollutants exiting small watersheds such as urban areas and construction sites. However, estimating the trap efficiency or designing a basin or trap to provide a pre-determined trap efficiency, is difficult, especially for dynamic conditions of water and sediment inflow. A conceptual dynamic model, called SedTrap, was developed that can be used to assess the varying removal efficiencies as a storm is routed through different sized basins or traps. The model uses the STELLA® modeling software from Iseesystems, Inc. to build a dynamic model to route both water and sediment through the system. Settling velocities are determined for a range of sediment sizes and temperatures using the Rubey-Watson law and compared to the more traditional Stokes’ law. The variation of efficiencies with time and by sediment size as the basin fills with sediment is also addressed. The results for the example used show a decrease in trap efficiencies with decreasing particle size, which leads to an increase in percent fine material of total sediment load at the outlet of the basin. This “fining” of the material coupled with the higher surface area per mass of the fine particles has implications for changes in the upstream-downstream concentrations of adsorbed contaminants.

Integrated modelling of conventional pollutants and organic contaminant fate in rivers: a microcosm study

A new conceptual dynamic integrated model is presented which can be used to describe both conventional pollutants and organic contaminant fate in rivers. The model is designed to assess the short-term fate of organic contaminants in two compartments (bulk water and benthic sediment), taking into account the effect of nutrient dynamics. The biodegradation submodel was refined using a microcosm (artificial river) study and Linear Alkylbenzene Sulphonate (LAS) as an example. Based on data generated during the microcosm study, the model was calibrated and validated in both steady state (continuous constant load) and dynamic (pulse load) conditions. The results show that the simulated data set agrees well with the measured data set. Furthermore, thorough investigation of the model output sensitivity to the model inputs was made, and the results show that the fate of LAS is sensitive to the following model input variables: ammonia nitrogen, dissolved oxygen, microbial biomass and readily biodegradable soluble COD, and the model parameters mainly related to the biodegradation submodel. The model provides good understanding of the interaction between conventional pollutants and organic contaminants fate in rivers.

An Investigation into PhD Supervisory Management Styles: Development of a dynamic conceptual model and its managerial implications

There has been a substantial increase in the number of candidates enrolled in PhD programmes in the past decade. Whereas the literature is relatively informative with its advice to candidates and supervisors, there is little evidence of research related to supervisory styles and changes of style over the supervisory period. This paper attempts to close that research gap by examining 60 items from the literature related to PhD completion. Eighty key variables identified from the literature were used to build a four‐quadrant supervisory style management grid based on the Blake and Moulton Managerial Grid model. The grid was subjected to a verification study through the results obtained from 12 in‐depth interviews with supervisors. Further, a hypothetical model was developed to examine changes in supervisory style over time, along with the managerial implications for supervisors. The study was taken within an Australian context using the European style of PhD structural practices which do not necessarily reflect the contemporary American model. The study has significant implications for alternative dissertation completion approaches where high levels of supervision are required.

Love and death in Goethe: "one and double"

Goethe, in association with his younger Romantic compatriots the Schlegels, Novalis, Fichte, and Schelling, struggled with the subject-object dichotomy, and tried to bridge the gap between self and other, consciousness and nature. His theory and practice prefigured the Romantics' determination to display and interrogate the linguistic and cultural structures informing their own thinking and modes of representation-what Goethe calls one's 'Vorstellungsart.' His work exploits, subverts, and supplants inherited conventions and signs, demonstrating with virtuosic irony that literature is a system of texts, pre-texts, and pre-established but dynamic conceptual models. ' Love and Death in Goethe:'One and Double' ' explores Goethe's use, in a wide range of his poetry and prose, of the theme of 'Liebestod' (love and death) and related embodiments of the paradox of unity in duality. Ellis Dye also examines Goethe's use of other themes related to love and death-the 'femme fatale,' the 'vagina dentata, Frau Welt,' the Lorelei, venereal disease, the 'Lustmord'-and considers issues of selfhood and individuation as well as the possibility that the love-death theme contains an implicit gender bias toward the existential fact of personal separateness. Poems, plays, and novels are dealt with, nevertheless, as works of art, not only as illustrations of an idea or as points of intersection in a system of rhetorical conventions, and are examined for intellectual cohesiveness, elegance, and integrity of design as well as special meanings and effects. ' Love and Death in Goethe:'One and Double' ' explores the meaning of the central theme of Romantic poetry in the works of the most important Romantic poet of all. Students of literary culture, both the lay reader and the Goethe specialist, will be enlightened by its approach and find pleasure and instruction in its revelations. Robert Ellis Dye is professor of German at Macalester College.

Dynamics of biogenic gas bubbles in peat and their effects on peatland biogeochemistry

Production and emission of peat gas has attracted great interest because substantial amounts of methane (CH4) are emitted to the atmosphere from peat soils. Many studies indicate supersaturation of CH4 in peat water, implying a high potential for gas bubble formation. However, observations of bubbles in peat are often only qualitatively described, and in most cases the presence of entrapped gas has been largely ignored in peatland studies. On the basis of a review of literature, a conceptual model of entrapped gas dynamics was developed and investigated using field and laboratory measurements at a poor fen in central Québec. We investigated variations in production and volume of gas and the effect of this gas on trace gas emissions, peat buoyancy, and pore water chemistry during 2002 and 2003. Measurements made with moisture probes and subsurface gas collectors revealed that gas volume varied throughout the growing season in relation to hydrostatic and barometric pressure. Shifts in entrapped gas volume were also coincident with changes in dissolved pore water CH4. The presence of these bubbles has important biogeochemical effects, including the development of localized CH4 diffusion gradients, alteration of local flow paths affecting substrate delivery, peat buoyancy, and the potential episodic release of CH4 via ebullition events. These interactions must be included in peatland models to describe accurately the hydrology and greenhouse gas emissions from these ecosystems and to make predictions about their response to environmental change.

The nature of spatial transitions in the Arctic

AbstractAim Describe the spatial and temporal properties of transitions in the Arctic and develop a conceptual understanding of the nature of these spatial transitions in the face of directional environmental change.Location Arctic tundra ecosystems of the North Slope of Alaska and the tundra‐forest region of the Seward Peninsula, AlaskaMethods We synthesize information from numerous studies on tundra and treeline ecosystems in an effort to document the spatial changes that occur across four arctic transitions. These transitions are: (i) the transition between High‐Arctic and Low‐Arctic systems, (ii) the transition between moist non‐acidic tundra (MNT) and moist acidic tundra (MAT, also referred to as tussock tundra), (iii) the transition between tussock tundra and shrub tundra, (iv) the transition between tundra and forested systems. By documenting the nature of these spatial transitions, in terms of their environmental controls and vegetation patterns, we develop a conceptual model of temporal dynamics of arctic ecotones in response to environmental change.Results Our observations suggest that each transition is sensitive to a unique combination of controlling factors. The transition between High and Low Arctic is sensitive primarily to climate, whereas the MNT/MAT transition is also controlled by soil parent material, permafrost and hydrology. The tussock/shrub tundra transition appears to be responsive to several factors, including climate, topography and hydrology. Finally, the tundra/forest boundary responds primarily to climate and to climatically associated changes in permafrost. There were also important differences in the demography and distribution of the dominant plant species across the four vegetation transitions. The shrubs that characterize the tussock/shrub transition can achieve dominance potentially within a decade, whereas spruce trees often require several decades to centuries to achieve dominance within tundra, and Sphagnum moss colonization of non‐acidic sites at the MNT/MAT boundary may require centuries to millennia of soil development.Main conclusions We suggest that vegetation will respond most rapidly to climatic change when (i) the vegetation transition correlates more strongly with climate than with other environmental variables, (ii) dominant species exhibit gradual changes in abundance across spatial transitions, and/or (iii) the dominant species have demographic properties that allow rapid increases in abundance following climatic shifts. All three of these properties characterize the transition between tussock tundra and low shrub tundra. It is therefore not surprising that of the four transitions studied this is the one that appears to be responding most rapidly to climatic warming.

A CONCEPTUAL DYNAMIC MODEL FOR EXTERNAL QUALITY IN KALANCHOE

Modelling quality in pot plants is still a weak feature in crop modelling research. This work aims at building a conceptual dynamic model for external quality (plant height and number of flower heads) in Kalanchoe blossfeldiana. Four experiments were conducted to quantify the effects of temperature and spacing schedules at two different planting dates. Five constant temperatures (18, 20, 22, 24 and 26°C) and nine spacing schedules, resulting from combinations of spacing at a given leaf area index (LAI: 1.6, 2, 3, 4 and 4.4) into a final plant density (31.1, 34.6, 43.4, 52.0 and 55.6 plants m-2) were studied. Stem length was modelled as the number of internodes (same as number of leaf pairs) times the average internode length. Plant height results from the stem length plus the uppermost pedicel length. The spacing schedules did not affect plant height, but total aerial dry mass (TDM, g plant-1), leaf area and number of flower heads were increased at earlier and wider spacing. In contrast, temperature had a significant effect on the average internode length (internode elongation rate linearly increased with temperature) and on the generative length (optimum response to temperature). However, internode appearance rate was not affected by temperature. Number of flower heads showed a positive linear relationship with TDM. Therefore, by simulating TDM the number of flower heads can be predicted. TDM was simulated based on the intercepted photosynthetic active radiation and light use efficiency. The reaction time showed a quadratic response to temperature, with a maximum rate of progress to flower at 23°C (10 days delay at 18°C). These modules need to be validated to form the basis of a year-round decision support system for Kalanchoe.

Dynamic neural networks with data assimilation

Neural networks (NNs) are often used as black-box techniques for the modelling of system relations. Standard NNs are static models, whereas in practice one often has to deal with dynamic systems or processes. In such cases, dynamic neural networks (DNNs) may be better suited. We will argue that the temporal processing in a DNN is highly related to that in dynamic physical-based models, and that this similarity provides the opportunity to include other important issues of conceptual dynamic models into an NN environment as well. In particular, we will propose to extend and upgrade NN models with data assimilation facilities. In hydrology one usually has to deal with complex dynamic systems, and lumped, aggregated, empirical, or fully black-box and data-driven techniques are often used for modelling. For this reason, the issues proposed here for upgrading of standard NNs may be particularly relevant for hydrology.

Monitoring approaches to assess bioaccessibility and bioavailability of metals: Matrix issues

Bioavailability and bioaccessibility are complex issues that determine whether or not adverse effects are to be expected when organisms or plants are exposed to contaminants. Clearly, the determinants of bioavailability and bioaccessibility must be understood if one is to monitor or, ultimately, predict the effects of metals. On the basis of a dynamic conceptual model, this article offers an analysis of the physicochemical and biological determinants underlying bioavailability and bioaccessibility. This analysis is used as the basis for a general monitoring strategy for assessing potentially and actually available and accessible metal fractions in the environmental matrices of water, soil, and sediment. We conclude that, lack of a universal expression of bioavailable and bioaccessible metal fractions precludes the presentation of a detailed monitoring strategy that is broadly applicable. Instead, we recommend that a critical assessment of the endpoints of determination become the basis for a need-specific monitoring strategy.