Flocculation model of cohesive sediment using variable fractal dimension

A new flocculation model using variable fractal dimension is proposed and validated with several experimental data and an existing model. The proposed model consists of two processes: aggregation and breakup due to flow turbulence. For aggregation process, the aggregate structure is considered to have the characteristic of self-similarity, the main concept of fractal theory. Under this assumption, a variable fractal dimension instead of a fixed one adopted by previous studies is utilized here for general cohesive sediment transport. For breakup, similar concept is adopted in a more empirical manner because breakup is too abrupt to entirely apply the concept of variable fractal dimension. By a linear combination of the formulations for aggregation and breakup processes, a flocculation model which can describe the temporal evolution of floc size is obtained. Flocculation model using variable fractal dimension is capable of predicting equilibrium floc size when compared with several experimental data sets using different types of mud provided that empirical coefficients are calibrated. Through model-data comparison with Manning and Dyer (Marine Geology 160:147–170, 1999), it is also clear that some of the empirical coefficients may depend on sediment concentration. Model results for the temporal evolution of floc size are less satisfactory, despite model results shows a more smooth “S-curve” for the temporal evolution of floc size as compared with the previous model using fixed fractal dimension. The proposed model is limited to mono-size of primary particle and dilute flow condition. These other features shall be investigated as future work.     

Agrodiversity v.2: An educational simulation tool to address some challenges for sustaining functional agrodiversity in agro-ecosystems

Functional agrodiversity can be useful and even essential for, i.e., the long-term sustainability of agriculture. However, still many aspects of this concept are not well understood. The interplay between species in diverse agro-ecosystems is based on processes as, i.e., competition, facilitation, and predator-prey relations. The net-effect of these processes on crop growth is not static and can change over time as the relative density of species change. The equilibrium state of a diverse agro-ecosystem might be far from optimum or even unproductive. This makes agrodiveristy a concept which is not easily grasped nor obtained or maintained. We believe that an agent-based model can facilitate learning on the topic of functional agrodiversity. In this paper, we present the agent-based simulation model, Agrodiversity v.2, developed in Netlogo 3.1.5. The model simulates a virtual diverse agro-ecosystem with four ecological agents. The user is challenged to explore ecological parameters and design a productive sustainable system. The model's “simplest playing level” shows that a proper balance between the co-existing species is necessary so that their ecological interactions allow the multi-species system to become self-organized and persist over time. It demonstrates the transient nature of profitable functional agrodiversity. Our analysis on the effects of using Agrodiversity v.2 on actual learning shows that the learning took place. Students increased the quality of their answers to paper-based individual questions on the topic from 29% during passive/conceptual teaching to 86% after the simulation session. On average students stated to have learnt 55% of their current knowledge through the workshop of which 76% was learnt by using the simulation.     

Natural control mechanisms in models of aquatic ecosystems

Based on cybernetic categories of natural control mechanisms, four generations of ecosystem models are distinguished: feed-forward, feedback, self-adaptation and self-organization models. The analysis of the natural control mechanisms in aquatic ecosystems suggests that different processes are controlled in different ways, and, although the four mechanisms were identified in historical sequence, they all operate simultaneously. The concept of self-organization of an ecosystem is introduced and specified for a model of an aquatic pelagic ecosystem. The concept of the ecosystem as a multilayer, multigoal and multiechelon hierarchical system with hierarchy of the levels of biological organization is also introduced.     

Natural control mechanisms in models of aquatic ecosystems

Based on cybernetic categories of natural control mechanisms, four generations of ecosystem models are distinguished: feed-forward, feedback, self-adaptation and self-organization models. The analysis of the natural control mechanisms in aquatic ecosystems suggests that different processes are controlled in different ways, and, although the four mechanisms were identified in historical sequence, they all operate simultaneously. The concept of self-organization of an ecosystem is introduced and specified for a model of an aquatic pelagic ecosystem. The concept of the ecosystem as a multilayer, multigoal and multiechelon hierarchical system with hierarchy of the levels of biological organization is also introduced.     

The main anammox-based processes,the involved microbes and the novel process concept from the application perspective

• The PNA, denitratation/anammox, and DAMO/anammox process are reviewed together. • Denitratation/anammox-based process is promising in mainstream treatment. • DAMO and denitratation processes realize the higher nitrogen removal efficiency. • The utilization of metabolism diversity of functional microbe is worth exploring. • An effective waste treatment system concept is proposed. Anammox technology has been widely researched over the past 40-year from the laboratory-scale to full-scale. It is well-known that in actual applications, the solo application of anammox is not feasible. Since both ammonium and nitrite are prerequisites based on the reaction mechanism, the pre-treatment of wastewater is necessary. With the combination of anammox process and other pre-treatment processes to treat the actual wastewater, many types of anammox-based processes have been developed with distinct nitrogen removal performance. Thus, in order to heighten the awareness of researchers to the developments and accelerate the application of these processes to the treatment of actual wastewater, the main anammox-based processes are reviewed in this paper. It includes the partial nitritation/anammox process, the denitratation/anammox (PD/A) process, the denitrifying anaerobic methane oxidation/anammox (DAMO/A) process, and more complex deuterogenic processes. These processes have made the breakthroughs in the application of the anammox technology, such as the combination of nitrification and PD/A process can achieve stability and reliability of nitrogen removal in the treatment of mainstream wastewater, the PD/A process and the DAMO/A have brought about further improvements in the total nitrogen removal efficiency of wastewater. The diversity of functional microbe characteristics under the specific condition indicate the wide application potential of anammox-based processes, and further exploration is necessary. A whole waste treatment system concept is proposed through the effective allocation of above mentioned processes, with the maximum recovery of energy and resources, and minimal environmental impact.     

Application of the New Keystone-Species Concept to Prairie Dogs: How Well Does It Work?

Abstract: It has been suggested that the keystone-species concept should be dropped from ecology and conservation, primarily because the concept is poorly defined. This prompted Power et al. (1996) to refine the definition: keystone species have large effects on community structure or ecosystem function (i.e., high overall importance), and this effect should be large relative to abundance (i.e., high community importance). Using prairie dogs ( Cynomys spp.) as an example, I review operational and conceptual difficulties encountered in applying this definition. As applied to prairie dogs, the implicit assumption that overall importance is a linear function of abundance is invalid. In addition, community importance is sensitive to abundance levels, the definition of community, and sampling scale. These problems arise largely from the equation for community importance, as used in conjunction with removal experiments at single abundance levels. I suggest that we shift from the current emphasis on the dualism between keystone and nonkeystone species and instead examine how overall and community importance vary (1) with abundance, (2) across spatial and temporal scales, and (3) under diverse ecological conditions. In addition, I propose that a third criterion be incorporated into the definition: keystone species perform roles not performed by other species or processes. Examination of how these factors vary among populations of keystone species should help identify the factors contributing to, or limiting, keystone-level functions, thereby increasing the usefulness of the keystone-species concept in ecology and conservation. Although the quantitative framework of Power et al. falls short of being fully operational, my conceptual guidelines may improve the usefulness of the keystone-species concept. Careful attention to the factors that limit keystone function will help avoid misplaced emphasis on keystone species at the expense of other species.     

Environmental indicators as tools for the management of estuaries—Methodology and case study of the Tejo estuary

The need for a better management of estuaries requires an environmental characterization following a methodology that allows the comparison of distinct estuarine systems and the assessment of their evolution. The peculiar characteristics of estuaries, in particular their intrinsic variability, make this characterization difficult and there is no commonly accepted general methodology available. The approach followed in freshwater ecosystems is generally based on the concept of environmental indicators, but such a concept has not been developed for estuaries. Indeed, a different approach is needed here, due to the spatial heterogeneity and the different time scales associated with the processes that control water quality. This paper presents a proposal for a methodology that starts with observed values and uses a procedure to integrate these values in time and space in order to calculatesignificant values, upon whichnormalized indicators are built which take into account criteria based either on legal, scientific or heuristic concentration limits. A normalization is carried out in two steps: (1) application of a mathematical operator to theignificant values, (2) transformation using the concept ofpenalty curves. This methodology may be complemented with the definition ofquality classes, particularly appealing and useful, as tools to communicate with decision makers and the public in general. Water quality data pertaining to the Tejo estuary are used to test the methodology.     

Soil Quality: A Review of the Science and Experiences in the USA

An increasing human population is placing greater demand on soil resources, and as a result degradation is taking place in many regions of the world. This is critical because soils perform a number of essential processes including supporting food and fiber production, influencing air quality through interaction with the atmosphere, and serving as a medium for storage and purification of water. The soil quality concept was introduced to complement soil science research by making our understanding of soils more complete and helping guide the use and allocation of labor, energy, fiscal, and other inputs as agriculture intensifies and expands to meet increasing world demands. Soil quality thus provides a unifying concept for educating professionals, producers, and the public about the important processes that soils perform. It also provides an assessment tool for evaluating current management practices and comparing alternative management practices. Soil attributes comprising a minimum data set have been identified, and both laboratory and field methods have been developed for measuring them. A soil quality index is being developed to normalize measured soil quality indicator data and generate a numeric value that can be used to compare various management practices or to assess management-induced changes over time. Using previously published data, we evaluated the soil quality index as a tool to assess a wide range of management practices in the Northern Great Plains. The index ranked the treatments: grazed fertilized tame pasture > moderately grazed > ungrazed> heavily grazed > annual cropping with no-tillage > conventionally tilled crop-fallow which agrees with the way they were subjectively ranked in the publications. The soil quality index shows potential for use as a management assessment tool.     

Soil quality: a review of the science and experiences in the USA

An increasing human population is placing greater demand on soil resources, and as a result degradation is taking place in many regions of the world. This is critical because soils perform a number of essential processes including supporting food and fiber production, influencing air quality through interaction with the atmosphere, and serving as a medium for storage and purification of water. The soil quality concept was introduced to complement soil science research by making our understanding of soils more complete and helping guide the use and allocation of labor, energy, fiscal, and other inputs as agriculture intensifies and expands to meet increasing world demands. Soil quality thus provides a unifying concept for educating professionals, producers, and the public about the important processes that soils perform. It also provides an assessment tool for evaluating current management practices and comparing alternative management practices. Soil attributes comprising a minimum data set have been identified, and both laboratory and field methods have been developed for measuring them. A soil quality index is being developed to normalize measured soil quality indicator data and generate a numeric value that can be used to compare various management practices or to assess management-induced changes over time. Using previously published data, we evaluated the soil quality index as a tool to assess a wide range of management practices in the Northern Great Plains. The index ranked the treatments: grazed fertilized tame pasture > moderately grazed > ungrazed > heavily grazed > annual cropping with no-tillage > conventionally tilled crop-fallow which agrees with the way they were subjectively ranked in the publications. The soil quality index shows potential for use as a management assessment tool.     

3D model for a secondary facultative pond

This paper describes a comprehensive model of wastewater treatment in secondary facultative ponds, which combines 3D hydrodynamics with a mechanistic water quality model. The hydrodynamics are based on the Navier-Stokes equation for incompressible fluids under shallow water and Boussinesq assumptions capturing the flow dynamics along length, breadth and depth of the pond. The water quality sub model is based on the Activated Sludge Model (ASM) concept, describing COD and nutrient removal as function of bacterial growth following Monod kinetics, except for Escherichia coli removal, which was modelled as first order decay. The model was implemented in the Delft3D software and was used to evaluate the effect of wind and the addition of baffles on the water flow pattern, temperature profiles in the pond and treatment efficiency. In contrast to earlier models reported in the literature, our simulation results did not show any significant improvement in COD removal (based on the ASM concept) with addition of baffles or under intermittent wind-induced mixing. However, E. coli removal efficiency, based on a first order decay approach, showed a fair improvement in the presence of baffles or intermittent wind-induced mixing. Furthermore, simulations with continuous wind effect showed a decrease in removal efficiency for COD but a further increase in E. coli removal efficiency. Such contrasting results for two different approaches in modelling could indicate that the first order decay concept might not be appropriate to describe all the interactions between biochemical processes in a pond. However, these interpretations remain theoretical, as the model needs validation with field data.     

What enables coexistence in plant communities? Weak versus strong species traits and the role of local processes

Explaining the coexistence of species that basically depend on the same resources has been a brainteaser for generations of ecologists. Different mechanisms have been proposed to facilitate coexistence in plant communities, where space is an important resource. Using a stochastic cellular automaton simulation model we analyze - separately and in combination - the influence of different species traits and processes which alter local competition on the coexistence of plant species over a fixed time horizon. We show that different species traits operate on different time scales in competition. We therefore suggest the concept of weak versus strong traits according to short- or long-term exclusion of species differing in these traits. As a consequence, highly non-linear trade-offs between weak and strong traits can result in communities. Furthermore, we found that trade-offs based on physiological species traits such as plant lifetime, dispersal range and plant growth, did not support broad and long-term coexistence—further processes such as density-dependent mortality and light-dependent colonization were necessary. This suggests that coexistence in plant communities requires (stabilizing) local processes to support the (equalizing) trade-offs in species traits.     

Abfallwirtschaftskonzept im Rahmen eines Integrierten Umweltmanagementsystems

Economic regulations on recycling and respective waste disposal legislation will increasingly demand the realization of new waste management concepts. They do not stem from a ministerial goal in itself, but instead offen the enterprizes a chance to develop their own waste disposal strategies with a goal toward the future. In the course of an Intra-company analysis, this waste disposal concept must take the operative organization, the relevant processes and manufacturing techniques, the accumulation of waste in the cost centers as well as the waste disposal and utilization into consideration. Fundamental principles include the environmental regulations applicable to the enterprize in the form of both federal decress and injunctions. An environmental examination report demonstrates the methodical possiblities for stock-taking and makes it possible to identify the measures necessary for improving the operational waste disposal situation. The mandatory data acquisition and a feasible waste monitoring network can be used in the course of environmental management system for making an expert opinion by an independent, reputable environmental verifier.     

Ableitung ökotoxikologisch begründeter Bodenqualitätskriterien am Beispiel Arsen

Background

A vast amount of data on the concentration of substances in soils is being generated in environmental monitoring programmes. This data has to be assessed in terms of effects on terrestrial biota. Benchmarks for such an assessment have been missing up to now. This gap has been filled by the development of a concept for the derivation of ecotoxicologically based soil quality criteria (SQC) and the application of this concept to environmentally relevant substances.

Objectives

The derivation method was applied to arsenic. The derivation process was described in detail from the compilation of data regarding effects on microbial processes, plants, and soil invertebrates to the formulation of a recommendation for an SQC.

Methods

The conceptual framework for the derivation of ecotoxicologically based SQC was developed after reviewing national and international concepts for the assessment of the effects of substances on terrestrial communities. For the assessment of arsenic effects, all relevant biotic processes and trophic levels have been taken into account. Moreover, soil characteristics that may affect the toxicity to biota have been reviewed.

Results

Effects of arsenic on biota may occur at soil background concentrations or slightly above. There are only a few studies in which the influence of soil characteristics, such as soil pH, soil texture, and soil organic carbon, on the effects of arsenic has been investigated systematically. That is why the SQC was oriented on soil background concentrations for sandy soils (5 mg As/kg soil dw). A comparison of the SQC derived in this work with ecotoxicologically based soilquality values from Canada, Denmark, the Netherlands, and the United States shows an average value of 16 mg As/kg, with a range between 5 and 34 mg/kg. The variations in the soil quality values are mainly due to differences in the derivation approaches.

Conclusions and Outlook

The concept applied is considered suitable for the derivation of SQC designed to protect terrestrial communities against direct effects of substances in soils. Therefore, its use is planned to derive SQC for other environmentally relevant substances. In addition to compensation factors, statistical methods should be taken into account to compensate for risks which cannot be quantified. Furthermore, there is the need for an assessment of indirect effects of soil contaminants on birds and mammals.     

A multidimensional decision-support approach to sustainable development planning

SUMMARY

The concept of sustainable development has become widely accepted as an instrumental objective of resource planning and environmental policy analysis. Nevertheless, applied planning approaches appropriate to this task have been slow in forthcoming. This paper suggests that one avenue for the application of sustainable development principles to resource management problems may be through multidimensional decision-support models. This approach recognizes that contemporary decision problems in the field of environmental planning are characterized by a diversity of structures and processes, incommensurable variables, and conflicting development objectives and constraints. On the basis of the articulated approach to sustainable development, a case study centred on Clayoquot Sound, British Columbia, Canada is presented. The case study serves to illustrate the efficacy of a multidimensional decision-support approach to sustainable development.     

Coexistence of the niche and neutral perspectives in community ecology

The neutral theory for community structure and biodiversity is dependent on the assumption that species are equivalent to each other in all important ecological respects. We explore what this concept of equivalence means in ecological communities, how such species may arise evolutionarily, and how the possibility of ecological equivalents relates to previous ideas about niche differentiation. We also show that the co-occurrence of ecologically similar or equivalent species is not incompatible with niche theory as has been supposed, because niche relations can sometimes favor coexistence of similar species. We argue that both evolutionary and ecological processes operate to promote the introduction and to sustain the persistence of ecologically similar and in many cases nearly equivalent species embedded in highly structured food webs. Future work should focus on synthesizing niche and neutral perspectives rather than dichotomously debating whether neutral or niche models provide better explanations for community structure and biodiversity.     

Identifizierung toxischer Verbindungen in Sedimenten: Ansätze zur Integration von Wirkung und Bioverfügbarkeit

Sediments play an important role for aquatic ecosystem functions. However, they also act as sink, storage and source of lipophilic toxicants and metals. Effect-directed analysis (EDA) is a powerful tool to identify compounds causing adverse effects. In order to avoid misinterpretations and biased prioritization bioavailability needs to be considered together with effects. Bioavailability is a complex process finally resulting in the transfer of a so far particle bound molecule to the target location within the organism where it causes an effect. In order to operationalize this concept for EDA it can be divided into several partial processes. These include desorption from sediments and thus bioaccessibility, equilibrium partitioning of desorbable compounds between sediment, water and organisms driven by activity, and toxicological bioavailability as a result of toxicokinetics including resorption, transport, metabolization and excretion. Bioaccessibility is based on desorption kinetics and can be simulated with mild extraction methods e.?g. using TENAX. Equilibrium partitioning can be simulated with partition-based dosing techniques. First results with these approaches indicate that consideration of bioavailability increases the significance of polar sediment-associated toxicants relative to classical non-polar contaminants such as polycyclic aromatic hydrocarbons.     

Multi-parameter renewal processes and simulation of forest fires

The concept of the renewal property is extended to processes indexed by a multidimensional time parameter. The definition given includes not only partial sum processes, but also Poisson processes and many other point processes whose jump points are not totally ordered. Various properties of renewal processes are discussed. Renewal processes are proposed as a basis for modelling the spread of a forest fire under a prevailing wind.

Systemic risks of genetically modified crops: the need for new approaches to risk assessment

Background

European chemicals legislation (registration, evaluation, authorisation and restriction of chemical substances (REACH)) requires a broad assessment of chemicals with respect to, inter alia, their health-relevant properties. Due to the extreme number of substances to be assessed and the limited current toxicological knowledge on their respective properties, REACH implicitly requires a paradigm change: away from knowledge generated mainly from costly animal experiments towards the use of mechanistic findings. Moreover, effect mechanisms at the biochemical or cellular level are essential when conclusions shall be drawn about "new" endpoints and mixtures of xenobiotics. This study (funded by the German Federal Environment Agency) describes examples of biochemical processes in the mammalian organism and how xenobiotics interfere with them. Interference with physiological processes expected to lead to adverse health effects is characterised as "toxicity pathway". The study describes toxicological endpoints not usually covered in routine animal testing and the respective toxicity pathways.

Results and conclusions

Screening for chemicals which exert effects via common toxicity pathways and subsequently conducting targeted short-term tests may generate new information about the toxicity of chemicals without performing extensive substance-by-substance animal experiments. Information on common toxicity pathways may also provide input for the assessment of mixture effects. The U.S. Environmental Protection Agency is working intensely on this concept. It involves the use of enormous amounts of data on relevant biochemical and cellular processes, which are generated by "high-throughput screening" methods, and then are combined with substance-specific kinetic data, experimental apical test outcomes and modelling. Current limitations in the regulatory use of this integrated approach on risk assessment will be outlined.     

Usefulness of the Umbrella Species Concept as a Conservation Tool

Abstract:  In the face of limited funding, knowledge, and time for action, conservation efforts often rely on shortcuts for the maintenance of biodiversity. The umbrella species concept—proposed as a way to use species requirements as a basis for conservation planning—has recently received growing attention. We reviewed the literature to evaluate the concept's general usefulness. An umbrella species is defined as a species whose conservation is expected to confer protection to a large number of naturally co-occurring species. This concept has been proposed as a tool for determining the minimum size for conservation areas, selecting sites to be included in reserve networks, and setting minimum standards for the composition, structure, and processes of ecosystems. Among the species suggested as potential umbrellas, most are large mammals and birds, but invertebrates are increasingly being considered. Eighteen research papers, most of which were based on hypothetical reserves or conservation networks, have provided evaluations of umbrella species schemes. These show that single-species umbrellas cannot ensure the conservation of all co-occurring species because some species are inevitably limited by ecological factors that are not relevant to the umbrella species. Moreover, they provide evidence that umbrella species from a given higher taxon may not necessarily confer protection to assemblages from other taxa. On the other hand, multi-species strategies based on systematic selection procedures (e.g., the focal species approach) offer more compelling evidence of the usefulness of the concept. Evaluations of umbrella species schemes could be improved by including measures of population viability and data from many years, as well as by comparing the efficiency of the proposed scheme with alternative management strategies.