森林生态系统发展和植物种群变化的热力学过程

随着生态学的发展,人们对自然生态系统的认识逐渐从对自然现象的记录、描述,发展为对机制的系统认识。热力学定律为人们提供了认识系统发展规律的理论基础,但在生态系统中的应用还处于起步阶段。基于前人关于生态系统可用能的研究。探讨了森林生态系统和植物种群变化的热力学过程。在生态系统水平上,把可用能耗散分为了植物耗散和环境耗散两个部分,并探讨了这两个过程之间的关系。第一次明确地提出蒸散是植物耗散的主要部分。在植物种群水平上,“可用能储存”与“可用能耗散”是决定植物竞争力的关键因子,在同一区域相同条件下,拥有更大可用能耗散能力的物种应当被优先选择。因此,群落中的优势物种应当比同层次的伴生种具有相对高的生长速度和更强的蒸腾能力。研究试图在热力学理论体系与实际生态系统的生理生态过程之间建立了纽带和桥梁,为开展森林生态系统的健康评估、深刻认识植物与环境的关系、以及评价物种竞争能力提供新的理论视野。     

Necessity and Inefficiency in the Generation of Waste

The laws of thermodynamics are employed as an analytical framework within which results about society's metabolism may be rigorously deduced in energetic and material terms. We demonstrate that the occurrence of waste is an unavoidable necessity in the industrial production of desired goods. Although waste is thus an essential qualitative element of industrial production, the quantitative extent to which waste occurs may vary within certain limits according to the degree of thermodynamic (in) efficiency with which these processes are operated. We discuss the question of which proportion of the amount of waste currently generated is due to thermodynamic necessity and which proportion is due to thermodynamic inefficiency.     

From Engineering Economics to Extended Exergy Accounting: A Possible Path from Monetary to Resource-Based Costing

The article describes the extended exergy accounting technique (EEA), a novel method for computing the cost of a commodity based on its resource-base equivalent value (as opposed to its monetary cost) that enables the analyst to perform more complete and meaningful assessments of a complex system. The claim made here is that the novelty, as well as the decisive advantage, of EEA consists in its being entirely and uniformly resource based, thanks to the inclusion in the system balance of exergetic fluxes equivalent to labor, capital, and environmental remediation costs. In this respect, EEA owes some of its structural formalism to Sraffa's network representation of the economic production of commodities by means of other commodities, which it extends by accounting for the unavoidable energy dissipation in the productive chain (whose economic implications were first discussed by Georgescu-Roegen), to Daly's pioneering work in resource-oriented economics, and to Szargut's cumulative exergy consumption method.
The representation of a process by means of its extended exergy flow diagram is discussed in this article, and it is argued that some of the issues that are difficult to address with a purely monetary approach can be properly resolved by EEA. The main shortcomings of EEA are its intrinsic locality in time and space: They are demonstrated to be necessary and not casual consequences of its very definition and of the nonuniformity of societal conditions. In the conclusions, some indications are given as to the possibility of using this new technique to complement (and extend) other current tools, such as life-cycle assessment or environmental footprint analysis.     

Life Cycle Assessment of Biomass‐based Combined Heat and Power Plants

Norway, like many countries, has realized the need to extensively plan its renewable energy future sooner rather than later. Combined heat and power (CHP) through gasification of forest residues is one technology that is expected to aid Norway in achieving a desired doubling of bioenergy production by 2020. To assess the environmental impacts to determine the most suitable CHP size, we performed a unit process‐based attributional life cycle assessment (LCA), in which we compared three scales of CHP over ten environmental impact categories—micro (0.1 megawatts electricity [MWe]), small (1 MWe), and medium (50 MWe) scale. The functional units used were 1 megajoule (MJ) of electricity and 1 MJ of district heating delivered to the end user (two functional units), and therefore, the environmental impacts from distribution of electricity and hot water to the consumer were also considered. This study focuses on a regional perspective situated in middle‐Norway's Nord‐ and Sør‐Trøndelag counties. Overall, the unit‐based environmental impacts between the scales of CHP were quite mixed and within the same magnitude. The results indicated that energy distribution from CHP plant to end user creates from less than 1% to nearly 90% of the total system impacts, depending on impact category and energy product. Also, an optimal small‐scale CHP plant may be the best environmental option. The CHP systems had a global warming potential ranging from 2.4 to 2.8 grams of carbon dioxide equivalent per megajoule of thermal (g CO₂‐eq/MJ_th) district heating and from 8.8 to 10.5 grams carbon dioxide equivalent per megajoule of electricity (g CO₂‐eq/MJ_el) to the end user.     

基于生命周期的户用沼气系统可用能核算——以广西恭城瑶族自治县为例

发展沼气生态农业可以实现资源的综合利用,带来经济效益与生态效益,同时解决我国农村地区能源短缺和环境污染问题。明确沼气系统内部的物质能量转化利用情况,可为沼气农业系统优化和效益提升提供科学依据。提出基于生命周期的户用沼气系统可用能核算方法,并以全国生态农业示范县——广西恭城瑶族自治县为例,核算了该县典型户用沼气系统建设、运行和利用单元投入产出的可用能流,分析了整个系统的可用能转化与利用效率。结果表明:系统的可用能投入为(1.06×108)kJ/a,可用能产出为(5.00×107)kJ/a,主要产出形式为沼渣;可用能转化率为48.82%,利用率为21.60%,其中沼气利用效率最高;系统产生的环境排放为(3.42×105)kJ/a,主要形式为系统利用单元沼气燃烧产生的CO2。由此可见,沼气生态农业可通过增加转化环节实现农业废弃物的再利用,系统可用能效率具备极大的提升空间,系统可持续性有待加强。可以考虑从改进工艺技术和改善发酵环境两方面提高户用沼气系统能量转化的能力,通过沼渣沼液综合利用技术方面的创新提高户用沼气系统的可用能利用效率。生命周期可用能核算方法可以更全面的反映系统的能量利用效率,便于诊断薄弱环节,为系统优化提供依据。     

扩展火用方法在区域生态经济驱动机制及效率研究中的应用

为分析区域生态退化的经济社会原因,针对以往扩展火用分析(EEA)应用以国家尺度为主,存在流通网络庞杂、规律辨识困难等问题,缩小空间尺度至县域,以宁夏彭阳为例,将生态经济系统划分为7个相互联系的部门,分别计算流通的物质、劳动力、资本的火用值,以分析驱动部门、要素和路径的扩展火用流特征并评价生态效率.结果表明: 彭阳县生态经济系统主要由农业和居民部门驱动,部门间31条流通路径平均扩展火用流值为0.80 PJ,高于该值的仅有8条流通路径,主要通过“居民部门劳动力输出和其他部门支持居民部门需求”两条连续路径驱动发展.矿产资源开采规模大,但直接输出区域外,无法从内部推动县域发展,反而由于资源开采加重了生态环境压力.县域2014年生态效率为68.1%,相当于10年前国内外国家尺度的中间水平,主要由服务和居民部门效率低造成.扩展火用分析有网络化、结构化的优势,可明确部门、要素和路径,突破驱动机制研究的“瓶颈”,对探究区域生态经济系统运行原理和选择优化模式具有一定适应性.区域尺度较国家大空间尺度分析更易识别生态经济系统驱动机制,能够明确指导区域管理部门改善生态环境压力.     

Estimation of ecological exergy using weighing parameters determined from DNA contents of organisms – a case study

We studied the changes of exergy and specific exergy with data of benthic macrofauna communities, periodically sampled along an estuarine gradient of eutrophication in the Mondego estuary (Western Portugal). Exergy estimates were calculated from organism biomass, based on weighing factors for the relative content of exergy per unit of biomass determined from DNA contents of organisms. Results were discussed in terms of both the macrofauna biomass production and the structural organisation of the system. Estimates for the exergy indices provided useful indications for the evaluation of environmental impact due to the eutrophication process. Different average values for the indices of exergy and specific exergy were estimated relatively to areas with different levels of eutrophication, in the spatial gradient of eutrophication. Higher exergy levels and lower exergy content per unit of biomass (specific exergy) were associated to populations more stabilized or areas less perturbed. Additionally, the index of specific exergy seemed capable of providing indications for the qualitative alterations in the communities (in temporal and spatial terms) that go in the direction of the observations made in this ecosystem.     

Life Cycle Assessment of a Magazine,Part I: Tablet Edition in Emerging and Mature States

Information and communication technology (ICT) is providing new ways to access media content. ICT has environmental benefits and burdens. The overall goal of the present study was to assess the environmental impacts of production and consumption of magazines read on tablets from a life cycle perspective. Important goals were to identify the activities giving rise to the main impacts and the key factors influencing the overall environmental impacts. Data gaps and uncertainties were also addressed. The results are compared against those for the print edition of the magazine in a separate article (part 2). The methodology used in the study was life cycle assessment. The environmental impacts assessed included climate change, cumulative energy/exergy demand, metal depletion, photochemical oxidant formation, particulate matter formation, terrestrial acidification, freshwater/marine eutrophication, fossil depletion, human toxicity, and ecotoxicity. The results indicate that content production can be the major contributor to environmental impacts if readers are few (as for the emerging version of the magazine studied). Assuming more readers (more mature version) or a larger file size for the tablet magazine, electronic storage and distribution may be the major contributor. Thus, in contrast to previous studies on electronic media, which reported a dominant impact of the use phase, this study found a higher impact for content production (emerging version) and electronic storage and distribution (mature version). However, with inefficient, low overall use of the tablet with a mature version of the tablet magazine, the greatest impact was shown to come from the reading activity (i.e., the use phase). In conclusion, the relative impacts of the tablet magazine would decrease considerably with high numbers of readers, their efficient use of the tablet (i.e., for many purposes over a long life of the device), and a smaller magazine file.     

Applying cumulative exergy demand (CExD) indicators to the ecoinvent database

Goal, Scope and Background Exergy has been put forward as an indicator for the energetic quality of resources. The exergy of a resource accounts for the minimal work necessary to form the resource or for the maximally obtainable amount of work when bringing the resource’s components to their most common state in the natural environment. Exergy measures are traditionally applied to assess energy efficiency, regarding the exergy losses in a process system. However, the measure can be utilised as an indicator of resource quality demand when considering the specific resources that contain the exergy. Such an exergy measure indicates the required resources and assesses the total exergy removal from nature in order to provide a product, process or service. In the current work, the exergy concept is combined with a large number of life cycle inventory datasets available with ecoinvent data v1.2. The goal was, first, to provide an additional impact category indicator to Life-Cycle Assessment practitioners. Second, this work aims at making a large source of exergy scores available to scientific communities that apply exergy as a primary indicator for energy efficiency and resource quality demand. Methods The indicator Cumulative Exergy Demand (CExD) is introduced to depict total exergy removal from nature to provide a product, summing up the exergy of all resources required. CExD assesses the quality of energy demand and includes the exergy of energy carriers as well as of non-energetic materials. In the current paper, the exergy concept was applied to the resources contained in the ecoinvent database, considering chemical, kinetic, hydro-potential, nuclear, solar-radiative and thermal exergies. The impact category indicator is grouped into the eight resource categories fossil, nuclear, hydropower, biomass, other renewables, water, minerals, and metals. Exergy characterization factors for 112 different resources were included in the calculations. Results CExD was calculated for 2630 ecoinvent product and process systems. The results are presented as average values and for 26 specific groups containing 1197 products, processes and infrastructure units. Depending on the process/product group considered, energetic resources make up between 9% and 100% of the total CExD, with an average contribution of 88%. The exergy of water contributes on the average to 8% the total exergy demand, but to more than 90% in specific process groups. The average contribution of minerals and metal ores is 4%, but shows an average value as high as 38% and 13%, in metallic products and in building materials, respectively. Looking at individual processes, the contribution of the resource categories varies substantially from these average product group values. In comparison to Cumulative Energy Demand (CED) and the abiotic-resource-depletion category of CML 2001 (CML’01), non-energetic resources tend to be weighted more strongly by the CExD method. Discussion Energy and matter used in a society are not destroyed but only transformed. What is consumed and eventually depleted is usable energy and usable matter. Exergy is a measure of such useful energy. Therefore, CExD is a suitable energy based indicator for the quality of resources that are removed from nature. Similar to CED, CExD assesses energy use, but regards the quality of the energy and incorporates non-energetic materials like minerals and metals. However, it can be observed for non-renewable energy-intensive products that CExD is very similar to CED. Since CExD considers energetic and non-energetic resources on the basis of exhaustible exergy, the measure is comparable to resource indicators like the resource use category of Eco-indicator 99 and the resource depletion category of CML 2001. An advantage of CExD in comparison to these methods is that exergy is an inherent property of the resource. Therefore less assumptions and subjective choices need to be made in setting up characterization factors. However, CExD does not coversocietal demand (distinguishing between basic demand and luxury), availability or scarcity of the resource. As a consequence of the different weighting approach, CExD may differ considerably from the resource category indicators in Eco-indicator 99 and CML 2001. Conclusions The current work shows that the exergy concept can be operationalised in product life cycle assessments. CExD is a suitable indicator to assess energy and resource demand. Due to the consideration of the quality of energy and the integration of non-energetic resources, CExD is a more comprehensive indicator than the widely used CED. All of the eight CExD categories proposed are significant contributors to Cumulative Exergy Demand in at least one of the product groups analysed. In product or service assessments and comparative assertions, a careful and concious selection of the appropriate CExD-categories is required based on the energy and resource quality demand concept to be expressed by CExD. Recommendations and Perspectives A differentiation between the exergy of fossil, nuclear, hydro-potential, biomass, other renewables, water and mineral/metal resources is recommended in order to obtain a more detailed picture of resource quality demand and to recognise trade-offs between resource use, for instance energetic and non-energetic raw materials, or nonrenewable and renewable energies. ESS-Submission Editor: Dr. Gerald Rebitzer (Gerald.Rebitzer@alcan.com)