Nitrogen metabolism in haloarchaea

The nitrogen cycle (N-cycle), principally supported by prokaryotes, involves different redox reactions mainly focused on assimilatory purposes or respiratory processes for energy conservation. As the N-cycle has important environmental implications, this biogeochemical cycle has become a major research topic during the last few years. However, although N-cycle metabolic pathways have been studied extensively in Bacteria or Eukarya, relatively little is known in the Archaea. Halophilic Archaea are the predominant microorganisms in hot and hypersaline environments such as salted lakes, hot springs or salted ponds. Consequently, the denitrifying haloarchaea that sustain the nitrogen cycle under these conditions have emerged as an important target for research aimed at understanding microbial life in these extreme environments. The haloarchaeon Haloferax mediterranei was isolated 20 years ago from Santa Pola salted ponds (Alicante, Spain). It was described as a denitrifier and it is also able to grow using NO₃ ^-, NO₂ ^- or NH₄ ⁺ as inorganic nitrogen sources. This review summarizes the advances that have been made in understanding the N-cycle in halophilic archaea using Hfx mediterranei as a haloarchaeal model. The results obtained show that this microorganism could be very attractive for bioremediation applications in those areas where high salt, nitrate and nitrite concentrations are found in ground waters and soils.     

Life Cycle of Titanium Dioxide Nanoparticle Production

Life cycle impact of emissions, energy requirements, and exergetic losses are calculated for a novel process for producing titanium dioxide nanoparticles from an ilmenite feedstock. The Altairnano hydrochloride process analyzed is tailored for the production of nanoscale particles, unlike established commercial processes. The life cycle energy requirements for the production of these particles is compared with that of traditional building materials on a per unit mass basis. The environmental impact assessment and energy analysis results both emphasize the use of nonrenewable fossil fuels in the upstream life cycle. Exergy analysis shows fuel losses to be secondary to material losses, particularly in the mining of ilmenite ore. These analyses are based on the same inventory data. The main contributions of this work are to provide life cycle inventory of a nanomanufacturing process and reveal potential insights from exergy analysis that are not available from other methods.     

城市系统碳循环:特征、机理与理论框架

城市是地表受人类活动影响最深刻的区域,城市系统碳循环在全球和区域碳过程中具有重要的地位和作用.提出了城市“自然-社会”二元碳循环的概念,探讨了城市系统碳循环的一般特征;分析了城市系统碳循环的内部机理,主要包括:城市系统碳储量和碳输入/输出通量的主要过程和途径、城市系统碳储量、碳通量和碳流通的生命周期分析、城市系统碳输入和碳输出的类型划分等;提出了基于系统层次划分和碳流通过程的城市系统碳循环的研究框架,分析了城市自然系统和城市经济系统的主要碳流通过程和环节,构建了城市系统碳循环研究的思路和理论框架;最后提出了城市系统碳循环领域未来的研究重点.     

生命周期方法在产业共生系统环境效益评价中的应用——研究进展及问题分析

近年来,产业共生作为产业生态学最具特征的领域引起了相关研究者的广泛关注。当前的研究逐渐从产业共生系统的定性描述分析转向定量的系统评价上。传统的产业共生系统环境效益评价仅仅关注共生系统本身,而忽视了占环境影响20%—50%的上、下游过程及替代过程的环境影响,为了得到客观的、系统的环境影响评价,将生命周期分析方法引入产业共生效益评价显得尤为重要。首先回顾了生命周期分析方法在产业共生研究中的发展过程,接着评述了3种生命周期分析方法在产业生态研究中的优劣势。并重点分析了将生命周期思想引入产业共生效益评价方法存在的功能单位设定问题及系统边界的选择问题。最后,呼吁为避免隐形污染的转移,必须尽快将生命周期分析的方法和管理理念引入我国生态工业园设计、规划、评价和管理的全过程中。     

On the Complexity of Life Cycle Inventory Networks: Role of Life Cycle Processes with Network Analysis

Determining the relevance and importance of a technosphere process or a cluster of processes in relation to the rest of the industrial network can provide insights into the sustainability of supply chains: those that need to be optimized or controlled/safeguarded. Network analysis (NA) can offer a broad framework of indicators to tackle this problem. In this article, we present a detailed analysis of a life cycle inventory (LCI) model from an NA perspective. Specifically, the network is represented as a directed graph and the “emergy” numeraire is used as the weight associated with the arcs of the network. The case study of a technological system for drinking water production is presented. We investigate the topological and structural characteristics of the network representation of this system and compare properties of its weighted and unweighted network, as well as the importance of nodes (i.e., life cycle unit processes). By identifying a number of advantages and limitations linked to the modeling complexity of such emergy‐LCI networks, we classify the LCI technosphere network of our case study as a complex network belonging to the scale‐free network family. The salient feature of this network family is represented by the presence of “hubs”: nodes that connect with many other nodes. Hub failures may imply relevant changes, decreases, or even breaks in the connectedness with other smaller hubs and nodes of the network. Hence, by identifying node centralities, we can rank and interpret the relevance of each node for its special role in the life cycle network.     

Connecting salt stress signalling pathways with salinity‐induced changes in mitochondrial metabolic processes in C3 plants

Salinity exerts a severe detrimental effect on crop yields globally. Growth of plants in saline soils results in physiological stress, which disrupts the essential biochemical processes of respiration, photosynthesis, and transpiration. Understanding the molecular responses of plants exposed to salinity stress can inform future strategies to reduce agricultural losses due to salinity; however, it is imperative that signalling and functional response processes are connected to tailor these strategies. Previous research has revealed the important role that plant mitochondria play in the salinity response of plants. Review of this literature shows that 2 biochemical processes required for respiratory function are affected under salinity stress: the tricarboxylic acid cycle and the transport of metabolites across the inner mitochondrial membrane. However, the mechanisms by which components of these processes are affected or react to salinity stress are still far from understood. Here, we examine recent findings on the signal transduction pathways that lead to adaptive responses of plants to salinity and discuss how they can be involved in and be affected by modulation of the machinery of energy metabolism with attention to the role of the tricarboxylic acid cycle enzymes and mitochondrial membrane transporters in this process.     

From Life Cycle Assessment to Life Cycle Management

Life cycle assessment (LCA) is a widely accepted methodology to support decision‐making processes in which one compares alternatives, and that helps prevent shifting of environmental burdens along the value chain or among impact categories. According to regulation in the European Union (EU), the movement of waste needs to be reduced and, if unavoidable, the environmental gain from a specific waste treatment option requiring transport must be larger than the losses arising from transport. The EU explicitly recommends the use of LCA or life cycle thinking for the formulation of new waste management plans. In the last two revisions of the Industrial Waste Management Programme of Catalonia (PROGRIC), the use of a life cycle thinking approach to waste policy was mandated. In this article we explain the process developed to arrive at practical life cycle management (LCM) from what started as an LCA project. LCM principles we have labeled the “3/3” principle or the “good enough is best” principle were found to be essential to obtain simplified models that are easy to understand for legislators and industries, useful in waste management regulation, and, ultimately, feasible. In this article, we present the four models of options for the management of waste solvent to be addressed under Catalan industrial waste management regulation. All involved actors concluded that the models are sufficiently robust, are easy to apply, and accomplish the aim of limiting the transport of waste outside Catalonia, according to the principles of proximity and sufficiency.     

Thermodynamics of natural selection II: Chemical Carnot cycles

This is the second in a series of three papers devoted to energy flow and entropy changes in chemical and biological processes, and to their relations to the thermodynamics of computation. In the first paper of the series, it was shown that a general-form dimensional argument from the second law of thermodynamics captures a number of scaling relations governing growth and development across many domains of life. It was also argued that models of physiology based on reversible transformations provide sensible approximations within which the second-law scaling is realized. This paper provides a formal basis for decomposing general cyclic, fixed-temperature chemical reactions, in terms of the chemical equivalent of Carnot's cycle for heat engines. It is shown that the second law relates the minimal chemical work required to perform a cycle to the Kullback-Leibler divergence produced in its chemical output ensemble from that of a Gibbs equilibrium. Reversible models of physiology are used to create reversible models of natural selection, which relate metabolic energy requirements to information gain under optimal conditions. When dissipation is added to models of selection, the second-law constraint is generalized to a relation between metabolic work and the combined energies of growth and maintenance.     

区域尺度陆地生态系统碳收支及其循环过程研究进展

地球系统的碳库和碳循环过程变化是影响气候系统的重要因素,而陆地生态系统的碳收支及其循环过程机制研究一直是全球气候变化成因分析、变化趋势预测、减缓和适应对策分析领域的科学研究热点。回顾了过去几十年区域尺度陆地生态系统碳循环和碳收支研究领域的国际前沿及其关键科学问题,并分析了我国在该研究领域的科技需求和发展方向。当前国际科学研究的热点和前沿领域主要包括:生态系统和区域碳储量和碳收支的清查、综合计量与碳汇认证,陆地生态系统碳通量的联网观测及其循环过程机制,陆地生态系统碳循环过程对气候变化响应野外控制试验,陆地生态系统水、碳、氮循环及其耦合关系机制和模拟模型研究等,同时指出在这些研究领域依然存在且急需解决的关键科学问题。我国近期的科技工作重点工作应该是努力构建天-地-空一体化的碳储量和碳收支动态监测体系、开展生态系统碳-氮-水耦合循环及其区域调控管理的前瞻性研究,定量评价中国生态系统的碳收支状况和增汇潜力,评估各种典型生态系统增汇技术的经济效益,为国家尺度的温室气体管理和碳交易机制与政策体系的建立提供可报告、可度量和可核查的科学数据和技术支持。     

Life cycle assessment of corn grain and corn stover in the United States

Background, aim, and scope  The goal of this study is to estimate the county-level environmental performance for continuous corn cultivation of corn grain and corn stover grown under the current tillage practices for various corn-growing locations in the US Corn Belt. The environmental performance of corn grain varies with its farming location because of climate, soil properties, cropping management, etc. Corn stover, all of the above ground parts of the corn plant except the grain, would be used as a feedstock for cellulosic ethanol. Materials and methods  Two cropping systems are under investigation: corn produced for grain only without collecting corn stover (referred to as CRN) and corn produced for grain and stover harvest (referred to as CSR). The functional unit in this study is defined as dry biomass, and the reference flow is 1 kg of dry biomass. The system boundary includes processes from cradle to farm gate. The default allocation procedure between corn grain and stover in the CSR system is the system expansion approach. County-level soil organic carbon dynamics, nitrate losses due to leaching, and nitrogen oxide and nitrous oxide emissions are simulated by the DAYCENT model. Life cycle environmental impact categories considered in this study are total fossil energy use, climate change (referred to as greenhouse gas emissions), acidification, and eutrophication. Sensitivities on farming practices and allocation are included. Results  Simulations from the DAYCENT model predict that removing corn stover from soil could decrease nitrogen-related emissions from soil (i.e., N₂O, NO _x , and NO₃ ⁻ leaching). DAYCENT also predicts a reduction in the annual accumulation rates of soil organic carbon (SOC) with corn stover removal. Corn stover has a better environmental performance than corn grain according to all life cycle environmental impacts considered. This is due to lower consumption of agrochemicals and fuel used in the field operations and lower nitrogen-related emissions from the soil. Discussion  The primary source of total fossil energy associated with biomass production is nitrogen fertilizer, accounting for over 30% of the total fossil energy. Nitrogen-related emissions from soil (i.e., N₂O, NO _x , and NO₃ ⁻ leaching) are the primary contributors to all other life cycle environmental impacts considered in this study. Conclusions  The environmental performance of corn grain and corn stover varies with the farming location due to crop management, soil properties, and climate conditions. Several general trends were identified from this study. Corn stover has a lower impact than corn grain in terms of total fossil energy, greenhouse gas emissions, acidification, and eutrophication. Harvesting corn stover reduces nitrogen-related emissions from the soil (i.e., N₂O, NO _x , NO₃ ⁻). The accumulation rate of soil organic carbon is reduced when corn stover is removed, and in some cases, the soil organic carbon level decreases. Harvesting only the cob portion of the stover would reduce the negative impact of stover removal on soil organic carbon sequestration rate while still bringing the benefit of lower nitrogen-related emissions from the soil. No-tillage practices offer higher accumulation rates of soil organic carbon, lower fuel consumption, and lower nitrogen emissions from the soil than the current or conventional tillage practices. Planting winter cover crops could be a way to reduce nitrogen losses from soil and to increase soil organic carbon levels. Recommendations and perspectives  County-level modeling is more accurate in estimating the local environmental burdens associated with biomass production than national- or regional-level modeling. When possible, site-specific experimental information on soil carbon and nitrogen dynamics should be obtained to reflect the system more accurately. The allocation approach between corn grain and stover significantly affects the environmental performance of each. The preferred allocation method is the system expansion approach where incremental fuel usage, additional nutrients in the subsequent growing season, and changes in soil carbon and nitrogen dynamics due to removing corn stover are assigned to only the collected corn stover.     

River stage response to alteration of Upper Mississippi River channels,floodplains, and watersheds

The Upper Mississippi River System (UMRS) is a large and diverse river system that changes character along its 1,200 mile network of rivers and canals and 2.6 million acres of floodplain. It supports more than 30 million people in its watershed, a significant commercial waterway, more than a million acres of “floodplain” agriculture and about one-half million acres of river-floodplain managed for fish, wildlife, and recreation. Large-scale geomorphology and climate patterns largely determine the hydrologic characteristics of a nested hierarchy of UMRS river reaches. The human impacts above are also important drivers determining hydrologic characteristics within the hierarchy. Understanding the relationship among physical and chemical processes and ecological responses is critical to implement an adaptive management framework for UMRS ecosystem sustainability. Historic or contemporary data from 42 locations were used to examine changes in UMRS hydrology and to demonstrate the utility of a multiple reference condition analysis for river restoration. A multivariate mathematical framework was used to show how river stage hydrology can be characterized by the variability, predictability, seasonality, and rate of change. Large-scale “geomorphic reaches” have distinct hydrologic characteristics and response to development throughout the UMRS region, but within navigation pool hydrology is similar among all impounded reaches regardless of geomorphic reach. Reaches with hydrologic characteristics similar to historic reference conditions should be examined to determine whether those characteristics support desired management objectives. Water levels can be managed, within limits to support navigation and agriculture, to more closely resemble natural hydrology for the benefit of a variety of species, habitats, and ecological processes.     

Tracking evolution of urban biogeochemical cycles: past,present, and future

This overview and synthesis paper focuses on the evolution of urban biogeochemical cycles across time. We synthesize empirical data and review existing literature, including papers in this special issue, and we propose the concept of “urban evolution.” The built environment often changes quickly in response to human activities, thus contributing to an urban evolution that affects structure, function, and ecosystem services of human settlements over time. Depending upon management, these changes can result in rapid losses of ecosystem functions/services or progress towards restoration. We explore urban evolution through empirical examples such as: (1) land development and nitrogen inputs within a metropolitan region over half a century; (2) watershed drainage by different forms of stormwater management over decades; (3) human-accelerated weathering in urbanized watersheds over decades; and (4) global salinization of freshwater across urbanizing landscapes over a century. We also synthesize concepts relevant to studying urban evolution of infrastructure and ecosystems including: (1) urban watersheds have challenged our whole notion of the “watershed approach” due to complex hydrologic boundaries and flow paths over time; (2) the urban hydrologic cycle evolves due to changing infrastructure and human water use over time; (3) the importance of extending research beyond individual sites using an urban watershed approach over space and time; (4) salinization as a universal tracer of watershed urbanization over time; (5) human-accelerated weathering of concrete and construction materials contributing to an “urban karst” over time; (6) human alteration of the carbon cycle in urban watersheds over time; and (7) detecting distinct biogeochemical signatures across cities globally over time. Our synthesis and this special issue suggest that urban biogeochemical cycles have exerted a major influence on the elemental composition of the Earth’s surface from local to global scales. A new global research agenda is needed to track the evolution of urban biogeochemical cycles as land development proceeds and infrastructure/management changes so we can better evaluate potential losses in ecosystem services, set realistic watershed and river restoration goals, and formulate effective environmental policy for Earth’s growing urban population.     

Attributional and Consequential Environmental Assessment of the Shift to Lead-Free Solders (10 pp)

- Goal, Scope, Background. As of July 1st, 2006, lead will be banned in most solder pastes used in the electronics industry. This has called for environmental evaluation of alternatives to tin-lead solders. Our life cycle assessment (LCA) has two aims: (i) to compare attributional and consequential LCA methodologies, and (ii) to compare a SnPb solder (62% tin, 36% lead, 2% silver) to a Pb-free solder (95.5% tin, 3.8% silver, 0.7% copper). Methods An attributional LCA model describes the environmental impact of the solder life cycle. Ideally, it should include average data on each unit process within the life cycle. The model does not include unit processes other than those of the life cycle investigated, but significant cut-offs within the life cycle can be avoided through the use of environmentally expanded input-output tables. A consequential LCA model includes unit processes that are significantly affected irrespective of whether they are within or outside the life cycle. Ideally, it should include marginal data on bulk production processes in the background system. Our consequential LCA model includes economic partial equilibrium models of the lead and scrap lead markets. However, both our LCA models are based on data from the literature or from individual production sites. The partial equilibrium models are based on assumptions. The life cycle impact assessment is restricted to global warming potential (GWP). Results and Discussion The attributional LCA demonstrates the obvious fact that the shift from SnPb to Pb-free solder means that lead is more or less eliminated from the solder life cycle. The attributional LCA results also indicate that the Pb-free option contributes 10% more to the GWP than SnPb. Despite the poor quality of the data, the consequential LCA demonstrates that, when lead use is eliminated from the solder life cycle, the effect is partly offset by increased lead use in batteries and other products. This shift can contribute to environmental improvement because lead emissions are likely to be greatly reduced, while batteries can contribute to reducing GWP, thereby offsetting part of the GWP increase in the solder life cycle. Conclusions The shift from SnPb to Pb-free solder is likely to result in reduced lead emissions and increased GWP. Attributional and consequential LCAs yield complementary knowledge on the consequences of this shift in solder pastes. At present, consequential LCA is hampered by the lack of readily available marginal data and the lack of input data to economic partial equilibrium models. However, when the input to a consequential LCA model is in the form of quantitative assumptions based on a semi-qualitative discussion, the model can still generate new knowledge. Recommendations and Outlook Experts on partial equilibrium models should be involved in consequential LCA modeling in order to improve the input data on price elasticity, marginal production, and marginal consumption.     

Probabilistic Forecast and Uncertainty Assessment of Hydrologic Design Values Using Bayesian Theories

Researches on hydrologic extreme events have great significance in reducing and avoiding the severe losses and impacts caused by natural disasters. When forecasting hydrologic design values of the hydrologic extreme events of interest by the conventional hydrologic frequency analysis (HFA) model, the results cannot take uncertainties and risks into account. In this article, in order to overcome conventional HFA model's disadvantages and to improve hydrologic design values’ forecast results, an improved HFA model named AM-MCMC-HFA is proposed by employing the AM-MCMC algorithm (adaptive Metropolis-Markov chain Monte Carlo) to HFA process. Differing with conventional HFA model, which is seeking single optimal forecast result, the AM-MCMC-HFA model can not only get the optimal but also the probabilistic forecast results of hydrologic design values. By applying to two obviously different hydrologic series, the performances of the model proposed have been verified. Analysis results show that four factors have great influence on hydrologic design values’ reliability, and also indicate that AM-MCMC-HFA has the ability of assessing the uncertainties of parameters and hydrologic design values. Therefore, by using the AM-MCMC-HFA model, hydrologic designs tasks can be operated more reasonably, and more rational decisions can be made by governmental decision-makers and public in practice.     

北京市住宅建筑生命周期碳足迹

从生命周期角度看,建筑碳足迹与能源和建材生产系统具有密切关系。随着技术的进步和节能政策的推进,中国能源的生产和使用,以及建材生产过程中的环境排放都随着时间在持续降低,这将间接地影响到建筑的环境表现。依据1990—2010年期间每5a的中国能源与建材生命周期清单数据,对北京市20年间住宅建筑系统开展生命周期评价和碳足迹核算,以揭示北京市住宅建筑系统的环境负荷变化特征。结果表明,北京市住宅建筑生命周期碳足迹随时间推移呈现降低趋势,主要来自能源系统和建材生产系统的碳减排贡献。不同结构建筑的碳足迹尽管有差异,但也呈现了相似的下降趋势。从生命周期阶段看,建筑碳足迹主要体现在建筑使用阶段和建材生产阶段。尽管建筑使用阶段的节能对于降低建筑生命周期碳足迹具有重要贡献,但节能在经济成本及环境成本方面而言是有限度的。在可持续的环境政策管理制定中,应从生命周期角度,统筹考虑协调各行业减碳的协调发展。论文同时也验证了在生命周期评价中考虑时间变量将有助于更好地利用生命周期评价结果支持环境可持续管理。结论对于城市规划的政策制定、量化环境表现是有益的。     

Uncovering the Fate of Critical Metals: Tracking Dissipative Losses along the Product Life Cycle

An increasing number of elements from the periodic table are being used in a growing number of products, enabling new material and product functionalities. Materials of high importance and high supply risks are usually referred to as critical materials. Many materials that are often considered critical are used in ways leading to their dissipative loss along the product life cycle. So far, the issue of material dissipation has been dealt with mainly on a rather aggregated level. Detailed knowledge on the occurrence and amount of dissipative losses in the life cycle of specific products is only scarcely available. Addressing this, a substance flow analysis of different critical metals along the life cycle of selected products is presented in this article. With regard to products used in Germany, the flows of indium and gallium used in copper‐indium‐gallium‐selenide (CIGS) photovoltaic cells, germanium used in polymerization catalysts, and yttrium used in thermal barrier coatings (TBCs) have been analyzed. The results comprise detailed knowledge about the life cycle stages in which dissipative losses occur and about the receiving media. In all case studies, a complete or almost complete dissipative loss can be observed, mainly to landfills and other material flows. In all case studies, material production can be identified as hotspots for dissipative losses. In two case studies fabrication and manufacturing (F&M for CIGS and TBCs) and in one case study end of life (polymerization catalysts) can be identified as further hotspots for dissipative losses. In addition, actions for reducing dissipation along the life cycle are discussed, targeting aspects such as the recovery of critical metals as by‐products, efficiency in F&M processes, and lack of recycling processes. Lack of economic incentives to apply more‐efficient technologies and processes already available is a key aspect in this regard.     

The hydraulic system of trees: theoretical framework and numerical simulation

Empirical studies pose the problem of the physiological integration of the tree organism, which is also important on the scale of ecosystems. Recently, spatially distributed models emerged, which approach this problem by reflecting the close linkage between physiological processes and the structures of trees and tree stands. In the case of water flow, the tree organism can be regarded as hydraulic system and the branched tree architecture as hydraulic network. Previous models of the hydraulic system either did not take into account the network structure, or they had shortcomings regarding the translation of the underlying physiological assumptions by the discrete computation method. We have developed a theoretical framework which takes the form of a numerical simulation model of tree water flow. A discrete initial boundary value problem (IBVP) combines the phenomena of Darcy flow, water storage and conductivity losses in the hydraulic network. The software HYDRA computes the solution of the IBVP. The theoretical derivation and model tests corroborate the consistent translation of the physiological assumptions by the computational method. Simulation studies enabled us to formulate hypotheses on the following points: (1) differences in the hydraulic segmentation between Picea abies and Thuja occidentalis, (2) responses of the hydraulic system to rapid transpiration changes and to a scenario of drought stress, and (3) how these responses depend on architectural quantities of the trees. The simulation studies demonstrated our possibilities of deriving theoretically well-founded hypotheses about the functioning of the hydraulic system and its relation to system structure. The numerical simulation model is designed as a tool for structure-function studies, which is able to treat tree architecture as independent variable. The model supports the integration of data on tree level, and it can be used for computer experiments which quantify the dynamics of the hydraulic system according to the concepts of system theory. Copyright 1999 Academic Press.     

Power: A new paradigm for energy use in sustainable construction

To achieve a sustainable management of resources, political and economic decision-makers need indicators to quantify their technical choice in relation with resource consumption. In this study, a new indicator that reflects the power demand next to energy demand of systems such as buildings is developed. The relevance of the proposed power indicator is tested through two different kinds of systems: retaining walls for civil and agricultural engineering and residential houses. It enables to highlight a close relation between this indicator and the high power energy sources that may exist at different steps of a building's life cycle. This dependence is presented as a better indicator of sustainability than a traditional energy account as it reflects the ability for the system to rely on flow energies rather than on stock energies.     

Giardia lamblia -- a model organism for eukaryotic cell differentiation

Giardia lamblia is a binucleated, flagellated protozoan parasite that inhabits the upper small intestine of its vertebrate hosts. The entire life cycle, which can be completed in vitro, is simple with cycling between a vegetative trophozoite and a highly resistant cystic form. The parasite is one of the earliest diverging eukaryotes known and more than 95% of the genome is sequenced. This makes Giardia an excellent model system for studies of basic eukaryotic processes like cell differentiation. In this review we will discuss recent data concerning Giardia differentiation with a focus on DNA replication and cytokinesis.     

Materials and Energy Flow Analysis of Paper Consumption in the United Kingdom, 1987-2010

This article presents the results of a life-cycle materials and energy flow analysis for the pulp and paper cycle in the United Kingdom. Material flows are reconstructed for the period be-tween 1987 and 1996 for all major processes associated with the paper cycle, and system energy requirements are calculated over this period using the best available data. Attention is drawn to the import dependence of U.K. paper demand, and the significant energy requirements associated with upstream forestry processes. The historical trend analysis is then used to model possible future developments in materials and energy consumption until 2010 under a variety of assumptions about process technology improvements, wastepaper utilization rates, and changing demand trends. The results indicate that policy options to increase recycling yield some energy benefits, but these are small by comparison with the benefits to be gained by reducing consumption of paper and improving process technology. The structure of the electricity supply industry in the United Kingdom means that global energy benefits could also be achieved by increasing the contribution from imported pulp.