水环境数学模型的研究进展

在作者多年研究工作和查阅大量文献资料的基础上,本文综述了环境数学模型国内外的研究现状、发展历史及未来趋势。重点介绍了这方面研究的最新进展。该文还介绍了本领域所涉及的理论和实际应用问题,提出了今后值得进行研究的若干前沿课题,给出了60余篇关于水环境数学模型研究的主要参考文献目录。     

Modelling photochemical oxidant formation, transport, deposition and exposure of terrestrial ecosystems

The chemical processes responsible for production of photochemical oxidants within the troposphere have been the subject of laboratory and field study throughout the last three decades. During the same period, models to simulate the atmospheric chemistry, transport and deposition of ozone (O(3)) from individual urban sources and from regions have been developed. The models differ greatly in the complexity of chemical schemes, in the underlying meteorology and in spatial and temporal resolution. Input information from land use, spatial and temporally disaggregated emission inventories and meteorology have all improved considerably in recent years and are not fully implemented in current models. The development of control strategies in both North America and Europe to close the gaps between current exceedances of environmental limits, guide values, critical levels or loads and full compliance with these limits provides the focus for policy makers and the support agencies for the research. The models represent the only method of testing a range of control options in advance of implementation. This paper describes currently applied models of photochemical oxidant production and transport at global and regional scales and their ability to simulate individual episodes as well as photochemical oxidant climatology. The success of current models in quantifying the exposure of terrestrial surfaces and the population to potentially damaging O(3) concentrations (and dose) is examined. The analysis shows the degree to which the underlying processes and their application within the models limit the quality of the model products.     

Mercury in the Mediterranean. Part 2: processes and mass balance

Mass balance of contaminants can provide useful information on the processes that influence their concentrations in various environmental compartments. The most important sources, sinks and the equilibrium or non-equilibrium state of the contaminant in individual environmental compartments can also be identified. Using the latest mercury speciation data, the results of numerical models and the results of recent studies on mercury transport and transformation processes in the marine environment, we have re-evaluated the total mercury (HgT) mass balance in the Mediterranean Sea. New calculations have been performed employing three distinct marine layers: the surface layer, the thermocline and the deep sea. New transport mechanisms, deep water formation and density-driven sinking and upwelling, were included in the mass balance calculations. The most recent data have even enabled the calculation of an approximate methylmercury (MeHg) mass balance. HgT is well balanced in the entire Mediterranean, and the discrepancies between inputs and outputs in individual layers do not exceed 20 %. The MeHg balance shows larger discrepancies between gains and losses due to measurement uncertainties and gaps in our knowledge of Hg species transformation processes. Nonetheless, the main sources and sinks of HgT (deposition and evasion) and MeHg (fluxes from sediment, outflow through the Gibraltar Strait) are in accordance with previous studies on mercury in the Mediterranean Basin. Mercury in the Mediterranean fish harvest is the second largest MeHg sink; about 300 kg of this toxic substance is consumed annually with sea food.     

Estimating the relevance of engineered carbonaceous nanoparticle facilitated transport of hydrophobic organic contaminants in porous media

Naturally occurring nanoparticles (NP) enhance the transport of hydrophobic organic contaminants (HOCs) in porous media. In addition, the debate on the environmental impact of engineered nanoparticles (ENP) has become increasingly important. HOC bind strongly to carbonaceous ENP. Thus, carbonaceous ENP may also act as carriers for contaminant transport and might be important when compared to existing transport processes. ENP bound transport is strongly linked to the sorption behavior, and other carbonaceous ENP-specific properties. In our analysis the HOC-ENP sorption mechanism, as well as ENP size and ENP residence time, was of major importance. Our results show that depending on ENP size, sorption kinetics and residence time in the system, the ENP bound transport can be estimated either as (1) negligible, (2) enhancing contaminant transport, or (3) should be assessed by reactive transport modeling. One major challenge to this field is the current lack of data for HOC-ENP desorption kinetics.     

What environmental fate processes have the strongest influence on a completely persistent organic chemical's accumulation in the Arctic?

Fate and transport models can be used to identify and classify chemicals that have the potential to undergo long-range transport and to accumulate in remote environments. For example, the Arctic contamination potential (ACP), calculated with the help of the zonally averaged global transport model Globo-POP, is a numerical indicator of an organic chemical's potential to be transported to polar latitudes and to accumulate in the Arctic ecosystem. It is important to evaluate how robust such model predictions are and in particular to appreciate to what extent they may depend on a specific choice of environmental model input parameters. Here, we employ a recently developed graphical method based on partitioning maps to comprehensively explore the sensitivity of ACP estimates to variations in environmental parameters. Specifically, the changes in the ACP of persistent organic contaminants to changes in each environmental input parameter are plotted as a function of the two-dimensional hypothetical “chemical space” defined by two of the three equilibrium partition coefficients between air, water and octanol. Based on the patterns obtained, this chemical space is then segmented into areas of similar parameter sensitivities and superimposed with areas of high default ACP and elevated environmental bioaccumulation potential within the Arctic. Sea ice cover, latitudinal temperature gradient, and macro-diffusive atmospheric transport coefficients, and to a lesser extent precipitation rate, display the largest influence on ACP-values for persistent organic contaminants, including those that may bioaccumulate within the polar marine ecosystems. These environmental characteristics are expected to be significantly impacted by global climate change processes, highlighting the need to explore more explicitly how climate change may affect the long-range transport and accumulation behavior of persistent organic pollutants.     

Prediction of overall persistence and long-range transport potential with multimedia fate models: robustness and sensitivity of results

The hazard indicators persistence (P) and long-range transport potential (LRTP) are used in chemicals assessment to characterize chemicals with regard to the temporal and spatial extent of their environmental exposure. They are often calculated based on the results of multimedia fate models. The environmental and substance-specific input parameters of such models are subject to a range of methodological uncertainties and also influenced by natural variability. We employed probabilistic uncertainty analysis to quantify variance in P and LRTP predictions for chemicals with different partitioning and transport behavior. Variance found in the results is so large that it prevents a clear distinction between chemicals. Additionally, only small improvements are observed when evaluating the results relative to a benchmark chemical. This can be explained by the dominance of substance-specific parameters and the only small direct influence of environmental parameters on P and LRTP as model outcomes. The findings underline the importance of learning how environmental conditions cause variability in substance behavior for improved substance ranking and classification.     

Multicompartmental fate of persistent substances

Background, Aim and Scope Modelling of the fate of environmental chemicals can be done by relatively simple multi-media box models or using complex atmospheric transport models. It was the aim of this work to compare the results obtained for both types of models using a small set of non-ionic and non-polar or moderately polar organic chemicals, known to be distributed over long distances. Materials and Methods Predictions of multimedia exposure models of different types, namely three multimedia mass-balance box models (MBMs), two in the steady state and one in the non-steady state mode, and one non-steady state multicompartment chemistry-atmospheric transport model (MCTM), are compared for the first time. The models used are SimpleBox, Chemrange, the MPI-MBM and the MPI-MCTM. The target parameters addressed are compartmental distributions (i.e. mass fractions in the compartments), overall environmental residence time (i.e. overall persistence and eventually including other final sinks, such as loss to the deep sea) and a measure for the long-range transport potential. These are derived for atrazine, benz-[a]-pyrene, DDT, α and γ-hexachlorocyclohexane, methyl parathion and various modes of substance entry into the model world. Results and Discussion Compartmental distributions in steady state were compared. Steady state needed 2–10 years to be established in the MCTM. The highest fraction of the substances in air is predicted by the MCTM. Accordingly, the other models predict longer substance persistence in most cases. The results suggest that temperature affects the compartmental distribution more in the box models, while it is only one among many climate factors acting in the transport model. The representation of final sinks in the models, e.g. burial in the sediment, is key for model-based compartmental distribution and persistence predictions. There is a tendency of MBMs to overestimate substance sinks in air and to underestimate atmospheric transport velocity as a consequence of the neglection of the temporal and spatial variabilities of these parameters. Therefore, the long-range transport potential in air derived from MCTM simulations exceeds the one from Chemrange in most cases and least for substances which undergo slow degradation in air. Conclusions and Perspectives MBMs should be improved such as to ascertain that the significance of the atmosphere for the multicompartmental cycling is not systematically underestimated. Both types of models should be improved such as to cover degradation in air in the particle-bound state and transport via ocean currents. A detailed understanding of the deviations observed in this work and elsewhere should be gained and multimedia fate box models could then be ‘tuned in’ to match better the results of comprehensive multicompartmental transport models. ESS-Submission Editor: Prof. Dr. Michael Matthies (matthies@uos.de)     

A review of radionuclides in tide-washed pastures on the Irish Sea coast in England and Wales and their transfer to food products

Close to the Sellafield Reprocessing Plant activity concentrations of many radionuclides including the long-lived 137Cs and actinides on tide-washed pastures bordering the Irish Sea are high compared with other terrestrial ecosystems in the United Kingdom. Despite the comparatively high deposition of radionuclides, contamination of agricultural products from tide-washed pastures is lower than would be predicted from studies in terrestrial ecosystems. This is because the main source of contamination in tide-washed pasture, radionuclides associated with sedimentary particles, has low availability for uptake by plant roots and in the gut of ruminants. Generalised Derived Limits (GDLs), published by the National Radiological Protection Board (NRPB) are estimates of environmental radioactivity concentrations which would potentially be radiologically significant. These provide a benchmark against which environmental measurements can be assessed. In the past, several comparisons of radioactivity concentrations in tide-washed pastures with GDLs have been made, but only some of these comparisons are valid since current approaches used to assess doses are not always strictly appropriate to these ecosystems. Directly applicable GDLs are needed, and are currently being developed by the NRPB.     

Comparison of the industrial source complex and AERMOD dispersion models: case study for human health risk assessment

Air quality models are typically used to predict the fate and transport of air emissions from industrial sources to comply with federal and state regulatory requirements and environmental standards, as well as to determine pollution control requirements. For many years, the U.S. Environmental Protection Agency (EPA) widely used the Industrial Source Complex (ISC) model because of its broad applicability to multiple source types. Recently, EPA adopted a new rule that replaces ISC with AERMOD, a state-of-the-practice air dispersion model, in many air quality impact assessments. This study compared the two models as well as their enhanced versions that incorporate the Plume Rise Model Enhancements (PRIME) algorithm. PRIME takes into account the effects of building downwash on plume dispersion. The comparison used actual point, area, and volume sources located on two separate facilities in conjunction with site-specific terrain and meteorological data. The modeled maximum total period average ground-level air concentrations were used to calculate potential health effects for human receptors. The results show that the switch from ISC to AERMOD and the incorporation of the PRIME algorithm tend to generate lower concentration estimates at the point of maximum ground-level concentration. However, the magnitude of difference varies from insignificant to significant depending on the types of the sources and the site-specific conditions. The differences in human health effects, predicted using results from the two models, mirror the concentrations predicted by the models.     

Characterization of flow and transport processes within the unsaturated zone of Yucca Mountain, Nevada, under current and future climates

This paper presents a large-scale modeling study characterizing fluid flow and tracer transport in the unsaturated zone of Yucca Mountain, Nevada, a potential repository site for storing high-level radioactive waste. The study has been conducted using a three-dimensional numerical model, which incorporates a wide variety of field data and takes into account the coupled processes of flow and transport in the highly heterogeneous, unsaturated fractured porous rock. The modeling approach is based on a dual-continuum formulation of coupled multiphase fluid and tracer transport through fractured porous rock. Various scenarios of current and future climate conditions and their effects on the unsaturated zone are evaluated to aid in the assessment of the proposed repository's system performance using different conceptual models. These models are calibrated against field-measured data. Model-predicted flow and transport processes under current and future climates are discussed.     

Low dose effects and non-monotonic dose responses for endocrine active chemicals: Science to practice workshop: Workshop summary

A workshop was held in Berlin September 12–14th 2012 to assess the state of the science of the data supporting low dose effects and non-monotonic dose responses (“low dose hypothesis”) for chemicals with endocrine activity (endocrine disrupting chemicals or EDCs). This workshop consisted of lectures to present the current state of the science of EDC action and also the risk assessment process. These lectures were followed by breakout sessions to integrate scientists from various backgrounds to discuss in an open and unbiased manner the data supporting the “low dose hypothesis”. While no consensus was reached the robust discussions were helpful to inform both basic scientists and risk assessors on all the issues. There were a number of important ideas developed to help continue the discussion and improve communication over the next few years.     

Suitability of process-based tree growth models for addressing tree response to climate change

Empirical models of tree growth have been used for many years to predict timber yields and other properties of trees. However, such models rely on measured relationships between tree growth and historic environmental conditions. As anthropogenic actions alter the environment, especially atmospheric composition, empirical models become less reliable and process-based models become more useful. Process-based models are challenged to simulate growth of structurally and physiologically complex organisms using explicit mathematical expressions to capture growth response to environmental conditions. In this review we summarize the physiological requirements of process-based models and examine the capabilities of six published models (CARBON, ECOPHYS, PGSM, TREE-BGC, TREGRO, W91) for simulating tree response to changes in environmental conditions (elevated temperature, increased CO(2) concentration, and enhanced concentrations of tropospheric ozone). These analyses indicate that current models are reliable integrators of environmental effects on individual processes (e.g. photosynthesis), but may be less reliable where physiological acclimation occurs or when extrapolated to growth of specific tree compartments.     

Ecological literacy and beyond: Problem-based learning for future professionals

Ecological science contributes to solving a broad range of environmental problems. However, lack of ecological literacy in practice often limits application of this knowledge. In this paper, we highlight a critical but often overlooked demand on ecological literacy: to enable professionals of various careers to apply scientific knowledge when faced with environmental problems. Current university courses on ecology often fail to persuade students that ecological science provides important tools for environmental problem solving. We propose problem-based learning to improve the understanding of ecological science and its usefulness for real-world environmental issues that professionals in careers as diverse as engineering, public health, architecture, social sciences, or management will address. Courses should set clear learning objectives for cognitive skills they expect students to acquire. Thus, professionals in different fields will be enabled to improve environmental decision-making processes and to participate effectively in multidisciplinary work groups charged with tackling environmental issues.     

Use of scientific inputs for environmental policymaking: the RAINS model and the Sulfur Protocols

This article discusses the use of Integrated Assessment Models for supporting the decision-making process in environmental issues. In particular, we discuss the case of sulphur emissions and the RAINS model, used in the process of negotiation of the Oslo Protocol (signed in June 1994), in relation to new targets for sulphur emissions reductions. To illustrate how scientific tools are not simply 'neutral' we discuss the particular case of Spain during the international negotiations leading to the final Protocol. The use of models as providers of scientific inputs for policy processes has grown during recent years. They are an aid to the policy-makers who may not know in depth all the issues on which they have the responsibility of taking decisions. We argue that these tools may indeed be helpful in their technical contribution but they can also have unrecognized consequences, depending on the way in which they are used in the policy-making process. They can also be used as a means to export cultural and technological patterns to late-comers from pioneer countries in the field of environmental policy. We conclude by proposing the post-normal science approach to deal with the complexity of environmental issues and to design more effective methods for policy formation.     

Modeling and interpreting bioavailability of organic contaminant mixtures in subsurface environments

Bioavailability often controls the fate of organic contaminants in surface and subsurface aquatic environments. Bioavailability can be limited by sorption, mass transfer, and intrinsic biodegradation potential and can be further altered by the presence of other compounds. This paper reviews current perspectives on the processes influencing subsurface contaminant bioavailability, how these processes are modeled, and how the relative role of the various processes can be assessed through bioavailability indices. Although these processes are increasingly well understood, the use of sophisticated models and indices often are precluded by an inability to estimate the many parameters that are associated with complex models. Nonetheless, the proper representation of sorption, mass transfer, biodegradation, and co-solute effects can be critical in predicting bio-attenuation. The influence of these processes on contaminant fate is illustrated with numerical simulations for the simultaneous degradation of toluene (growth substrate) and trichloroethylene (nongrowth cometabolite) in hypothetical, aerobic, solid-water systems. The results show how the relative impacts on contaminant fate of the model's various component processes depends upon system conditions, including co-solute concentrations. Slow biodegradation rates increase the inhibition effects of a cometabolite and suppress the rate enhancement effects of a growth substrate. Irrespective of co-solute effects, contaminant fate is less sensitive to biodegradation processes in systems with strong sorption and slow desorption rates. Bioavailability indices can be used to relate these findings and to help identify appropriate modeling simplifications. In general, however, there remains a need to redefine such indices in order that bioavailability concepts can be better incorporated into site characterization, remediation design, and regulatory oversight.     

Rigorous uncertainty assessment in contaminant transport inverse modelling: a case study of fluoride diffusion through clay liners

Inverse methods used in assessing landfill liner design have not yet taken advantage of current developments in inverse procedures. Here, a method for inverting contaminant transport models is presented including a general error model and procedures for differentially weighted multiple response regression. General error models are employed in cases where the residuals are heteroscedastic and correlated, and lead to valid inference on model parameter and predictive uncertainty. The Shuffled Complex Evolution algorithm is used to optimise model parameters. Model parameter uncertainty is assessed by exploring the posterior probability distribution with the Metropolis algorithm, a Markov chain Monte Carlo sampling method. The inverse method is applied to simultaneously determine the sorption and diffusion parameters from laboratory diffusion cell experiments. In these experiments, fluoride migration through kaolin clays was measured by sampling the source and collector cells over time. To uniquely determine the transport model parameters, it was necessary to simultaneously fit the observed data from two independent diffusion cell experiments with different initial concentrations. The jointly fitted transport model parameters compared well with those fitted to independent batch experiments.     

Reflections about three influential Ambio articles impacting environmental biogeochemistry research and knowledge: This article belongs to Ambio’s 50th Anniversary Collection. Theme: Environmental contaminants

Reflections about three influential environmental contaminants papers published in Ambio are presented. The PCB Story by Jensen in (1972) had a very important influence on environmental chemistry. This is captured by way of comments and personal anecdotes. Wania’s and MacKay’s (1993) paper highlights the physical chemistry underlying transport of PCBs and organochlorine pesticides from temperate zone ecosystems to Polar Regions. Their paper exemplifies how principles of chemistry and environmental processes informed understanding the biogeochemical cycles of chemicals of environmental concern (CEC). Mergler et al.’s (2007) paper reviews knowledge of methyl mercury exposure and impacts in humans and served as an example of how to approach exposure and human health concerns for all CECs. All great progress. Then, the question: “How we missed for two decades the importance of plastics in the environment identified in a paper published the same year as The PCB Story? Are we missing yet another important environmental contaminant now?     

Plant uptake and transport models for neutral and ionic chemicals

BACKGROUND: Models for predicting uptake and transport of chemicals in plants are applied in pesticide design, risk assessment, and environmental biotechnology. OBJECTIVE: This review considers the theoretical basics of the most popular models, and discusses what they have in common. The line is drawn between models for neutral compounds, and models for weak and strong electrolytes. MAIN FEATURES: Neutral Compounds. Neutral compounds undergo only very few processes inside plants (lipophilic interactions, metabolism), in contrast to weak electrolytes. The models developed for neutral compounds are widely applied in the risk assessment of environmental contaminants, but are not of much use for weak electrolytes, such as pesticides. Weak electrolytes. A very important process for weak electrolytes is the 'ion trap', which traps chemicals that dissociate inside plant cells. This is considered in the popular models of Kleier, Satchivi and Briggs. Other relevant processes for electrolytes are electrophilic interactions, speciation and complex formation. None of the currently used models considers these processes. CONCLUSIONS: The accuracy of models for neutral compounds is satisfactory, but the prediction of electrolyte behavior inside plants is still quite difficult due to gaps in knowledge.