基于生态能量视角的我国小水电可持续性分析

我国的小水电开发经历了以解决农村地区用电短缺到当前以促进节能减排、清洁能源建设为目的的转变。运用生态能量分析的方法之一——能值分析方法,选取贵州省安龙县红岩二级水电站为案例,对其建设与运行的可持续性进行了系统分析,并与国内外大水电的相关指标进行了平行对比。结果表明:该水电站2010年电力产出的能值转换率为1.03×105sej/J,其可再生性比例为52.01%,在能值产出率、环境负载率和可持续能力等方面的表现均好于大水电。但其能值交换率为0.58,表明2010年水电上网价格偏低。小水电的不稳定运行也使其系统能值指标呈现波动变化,当实际发电量为设计发电量的50%时,水电的能值转换率接近于湄公河上大坝生产水电的能值转换率,可持续性指标的值从6.12急剧降到3.01。系统评估水电资源,作好流域小水电总体开发规划,保证小水电系统稳定运行是提高其可持续性的关键之一。     

Quantifying electricity generation and waste transformations in a low-cost, plug-flow anaerobic digestion system

Methane production, electricity production, and wastewater transformations were quantified for a digestion system that combines biogas from a swine digester and dairy digester in Costa Rica. The low-cost, plug-flow digesters were not heated and were operated in the lower portion of the mesophilic range (25–27 °C).The dairy digester produced 27.5 m³/day of biogas with 62.6% methane and reduced organic matter (COD) by 86%. The swine digester produced 6.0 m³/day of biogas with 76.4% methane and reduced COD by 92%. Combining biogas from a swine and dairy digester, increased electricity production due to the higher biogas production rate of the dairy farm and the higher quality biogas obtained from the swine farm. The farm’s 2-h peak electricity demand (12.9 kW/day) was 81.8% met. The electricity was produced using manure equivalent to the quantity excreted by 5 dairy cows and 40 pigs remaining in corrals 100% of the time.The $21,000 capital cost of the digester project will be recovered in 10.1 years through electricity savings and reductions in wastewater fines. If the generator were more appropriately sized for the farm, the capital recovery time would have been 7.6 years.     

Status quo and perspectives of biogas production for energy and material utilization

Biogas is in many respects a serious alternative to other fossil resources and complements other renewable energy sources from wind and sun. Biogas can be produced in many places decentrally. Its energy potential is high, and it is widely used in the EU and all over the world. With more than 16,000 ktoe of oil equivalent in the EU in 2016, it corresponds to approximately 8% of the total primary energy produced by renewable energies in the EU, produced with nearly 17,000 biogas plants. Nevertheless, the production costs of biogas and its products like energy, heat, and fuel are still too high. Kost et al. (2018) show a comparison of electricity generation costs of different renewable energies and their future potentials. While electricity from huge biogas plants offers generation costs from 10 to 15 ct/kWh, electricity from onshore wind and huge solar systems offers generation costs from 4 to 8 ct/kWh. Although substantial progress has been made with regard to substrate use, production techniques and market designs, many more innovations are needed throughout the biogas value chain for it to be competitive in energy markets without high subsidies. As several papers in the special issue on biogas show, there are numerous innovations and product designs with regard to energy and material uses that could maintain or even increase the importance of biogas production both within and outside of the EU. There are many potential benefits of biogas, as it offers high shares of produced renewable energies as well as large amounts of material products like digestates and in future maybe products of higher value such as proteins or lactic acids.     

Emergy analysis of cassava chips-suitable feedstock for fuel ethanol in China

The theory and indices of Odum's concept of emergy are explained. The environmental and economic inputs and sustainability of cassava chips production system are evaluated by emergy methodology. The emergy indices of cassava chips production system were calculated as follows: Tr (transformity) was 6.85E + 11 sej/kg, EYR (emergy yield ratio) was 1.11, ELR (environmental loading ratio) was 1.75, EIR (emergy investment ratio) was 9.33, and ESI (emergy sustainability indice) was 0.63. The emergy indices of four kinds of feedstock for fuel ethanol—corn, wheat, sugarcane, and cassava chips—were compared. Least solar energy was consumed when taking cassava chips as feedstock for fuel ethanol. According to the emergy indices, using cassava chips as the feedstock of fuel ethanol is helpful for sustainable development in China.     

Waste treatment and biogas quality in small-scale agricultural digesters

Seven low-cost digesters in Costa Rica were studied to determine the potential of these systems to treat animal wastewater and produce renewable energy. The effluent water has a significantly lower oxygen demand (COD decreased from 2968 mg/L to 472 mg/L) and higher dissolved nutrient concentration (NH₄-N increased by 78.3% to 82.2 mg/L) than the influent water, which increases the usefulness of the effluent as an organic fertilizer and decreases its organic loading on surface waters. On average, methane constituted 66% of the produced biogas, which is consistent with industrial digesters. Through principle component analysis, COD, turbidity, NH₄-N, TKN, and pH were determined to be the most useful parameters to characterize wastewater. The results suggest that the systems have the ability to withstand fluctuations in the influent water quality. This study revealed that small-scale agricultural digesters can produce methane at concentrations useful for cooking, while improving the quality of the livestock wastewater.     

An environmental sustainability assessment of China’s cement industry based on emergy

As one of important building materials, the sustainability of cement production is widely concerned in the world. This research evaluated the sustainability of China’s cement industry in 2010 using emergy analysis. Several emergy based indicators were adopted to describe the comprehensive performance of this system from different angles, including Percentage of renewability (%R), Unit emergy value (UEV), Emergy yield ratio (EYR), Emergy exchange ratio (EER), Environmental load ratio (ELR) and Emergy sustainable index (ESI). The research results show that (1) Mineral resources have absolute contribution to China’s cement production; (2) Coal is the main energy source for China’s cement industry; (3) China’s cement industry has relatively weak competition ability due to relatively high ratio of purchased inputs; (4) China’s other industries have benefited greatly from this industry by exchanges; (5) China’s cement industry cannot keep sustainable in the long run due to its high environmental load; (6) the UEV of Chinese cement in 2010 is 3.64E15 sej/t (based on the emergy baseline 15.83E24 sej/yr). Finally, the related policy implications are proposed from four aspects, including (1) Accelerating the adjustment of process structure and technical innovation; (2) Promoting the substitution of raw materials or fuels; (3) Raising the price of cement products; (4) Decreasing the export of cement products.     

Ecological accounting for an integrated “pig–biogas–fish” system based on emergetic indicators

With the expansion of urbanization in China, the integrated biogas-utilization system has gained its popularity for both renewable energy production and multi-level utilization of organic waste. To appraise the ecological performance of the integrated biogas system, systematic accounting is undertaken for an integrated “pig–biogas–fish” system in Hubei province, China. Based on Odum's concept of embodied solar energy as a unified measure for environmental resources, human labors and purchased goods, a set of emergetic indicators are employed to quantify the system sustainability. The results reveal that in a 20-year designed lifetime scenario, 94.69% of the total emergy inputs for the “pig–biogas–fish” system are attributed to purchased social resources. Three kinds of products, namely pig, biogas, fish are taken into consideration, and transformity of the “pig–biogas–fish” system is calculated as 1.26E + 05 seJ/J. Compared with the Chinese conventional agriculture system, the integrated biogas system shows a higher sustainability. Given that most biogas systems have a lifespan less than 20 years, for the “pig–biogas–fish” system, six other scenarios with different lifespans are studied to investigate the impact of the lifespan on sustainability. The findings suggest that the “pig–biogas–fish” system should be well operated for at least 8 years to prove its advantage in ecological economy over the conventional agriculture system. This has essential policy implications that local government should strengthen subsequent management on biogas production to extend the practical service life of the biogas system.     

基于能值分析的我国小水电生态影响研究

如何系统定量地评价小水电开发过程所引起的景观变化、河流局部断流等生态影响,是平息争议、进行合理规划与开发小水电前提之一。运用能值分析方法,以贵州省赤水市观音岩水电站为例,将小水电建设、运行的资源投入,以及河道中水流的时空改变所导致生态服务功能的损失纳入核算体系,对其生态影响进行综合定量评估。从2010年的实际结果来看,由于河流断流,导致水坝下游生态系统服务功能的能值损失为2.77×1018sej,占到了系统建设运行总投入的44.84%,其中重点保护鱼种在影响河段的生境破坏是最大的能值损失。若不考虑下游生态系统服务功能损失,系统的环境负载率为1.92,可持续性指标为1.22;而考虑下游生态影响之后,系统环境负载率增大至4.26,可持续性指标减小为0.34。研究表明,小水电的开发必须遵循适度开发、规划优先,保障河流最基本的生态需水底线,是协调小水电开发和河流健康矛盾、追求小水电持续发展的刚性要求。     

黄土高原典型流域种植业发展模式的能值分析

为客观评估和比较退耕还林后黄土高原典型小流域不同种植业发展模式的稳定性和可持续性,本研究通过能值分析方法,定量分析了粮食和果树兼作、粮食生产为主和果树种植为主3种典型流域种植业系统的能值投入和产出情况,建立能值分析指标体系,在自然资源压力、社会和经济发展水平方面进行比较,进而对3种模式的系统可持续性进行评估.结果表明: 黄土高原典型流域不同类型种植业系统外部辅助能值均占总能值投入的75%以上,且其中不可更新能值所占比例远大于可更新能值,由此造成了能值自给率低而环境承载率高的特点;流域粮食种植业生产具有高投入、低产出的特点,而水果种植和粮果兼作具有高投入、高产出的特点,3种模式能值密度均达到全国农业经济系统平均水平2倍以上,其中,粮食生产为主的模式净能值产出率最低而粮果兼作型最高;流域种植业能值可持续发展指数均<1,能值/环境可持续指标均远低于全国农业系统平均水平,可持续发展能力较低,以粮食和果树兼作的模式可持续发展指数最高.3种模式比较发现,粮果兼作发展模式在流域种植业发展中具有相对较好的发展能力和较高的系统稳定性,能值生产效率适中且可持续性最高,因此黄土高原地区以流域为单元的农业发展应该更加偏向于考虑多产业综合的复合结构生产方式.     

西部欠发达地区生态经济系统能值分析——以青海省海西蒙古族藏族自治州为例

青海省海西蒙古族藏族自治州（简称海西州）生态环境脆弱,快速发展的工业活动对当地生态环境造成严重破坏。海西州地处青藏高原东北部,是我国重要的生态安全屏障之一,在全国生态建设中处于特殊地位。能值分析法是一种基于热力学理论的环境核算方法。利用能值分析法对海西州生态经济系统运行现状进行评估;并应用能值指标评价海西州生态经济系统的可持续发展水平;通过对能值指标的时间序列分析揭示海西州生态经济系统的发展趋势,以期为海西州生态经济系统的可持续发展提供参考依据。研究结果表明,2016年支撑海西州生态经济系统运行的总能值投入量为6.69×10²⁴ sej,是2010年总能值投入量的1.94倍。在2010-2016年的7年内,不可更新资源的能值投入占当年总能值投入量的比例均超过90%,而可更新资源能值投入量与从系统外输入到海西州的能值量占比均较低。基于能值的指标分析显示：海西州的人均能值使用量、能值密度、能值货币比率、环境负载率分别从2010年的8.84×10¹⁸ sej/人、1.15×10¹³ sej/m²、3.05×10¹⁴ sej/US$、103.02增加到2016年的1.65×10¹⁹ sej/人、2.22×10¹³ sej/m²、9.12×10¹⁴ sej/US$、213.47;而相应的能值产出率、能值可持续发展指数则分别从2010年的2.66×10³和25.84降低到2016年的1.23×10³和5.74。研究结果表明虽然海西州经济得到发展、人民生活质量得到提高,而经济发展对当地不可再生资源依赖较大,给环境造成的压力不断增加。为从长远角度实现海西州的可持续发展,亟需转变经济发展方式,降低对不可更新能源的过度开发。此外,研究结果显示,海西州的能值交换率小于1,这说明研究时间范围内,海西州在对外贸易过程中处于不利地位,因此需增加单位产品的附加值以促进能值流的合理流动。     

Assessing the potential for up-cycling recovered resources from anaerobic digestion through microbial protein production

Anaerobic digesters produce biogas, a mixture of predominantly CH₄ and CO₂, which is typically incinerated to recover electrical and/or thermal energy. In a context of circular economy, the CH₄ and CO₂ could be used as chemical feedstock in combination with ammonium from the digestate. Their combination into protein-rich bacterial, used as animal feed additive, could contribute to the ever growing global demand for nutritive protein sources and improve the overall nitrogen efficiency of the current agro- feed/food chain. In this concept, renewable CH₄ and H₂ can serve as carbon-neutral energy sources for the production of protein-rich cellular biomass, while assimilating and upgrading recovered ammonia from the digestate. This study evaluated the potential of producing sustainable high-quality protein additives in a decentralized way through coupling anaerobic digestion and microbial protein production using methanotrophic and hydrogenotrophic bacteria in an on-farm bioreactor. We show that a practical case digester handling liquid piggery manure, of which the energy content is supplemented for 30% with co-substrates, provides sufficient biogas to allow the subsequent microbial protein as feed production for about 37% of the number of pigs from which the manure was derived. Overall, producing microbial protein on the farm from available methane and ammonia liberated by anaerobic digesters treating manure appears economically and technically feasible within the current range of market prices existing for high-quality protein. The case of producing biomethane for grid injection and upgrading the CO₂ with electrolytic hydrogen to microbial protein by means of hydrogen-oxidizing bacteria was also examined but found less attractive at the current production prices of renewable hydrogen. Our calculations show that this route is only of commercial interest if the protein value equals the value of high-value protein additives like fishmeal and if the avoided costs for nutrient removal from the digestate are taken into consideration.     

An emergy evaluation of the sustainability of Chinese crop production system during 2000–2010

Crop production systems are the basis of human survival and development because they can produce grain and industrial raw materials. As one of the largest agricultural countries in the world, the sustainability of China's crop production system is being concerned widely with its economic development and increasing population. This study adopted emergy analysis to explore the comprehensive performance of this system. A set of emergy based indicator system was used to investigate its economic benefit, environmental pressure and sustainability from 2000 to 2010. The study results show that the purchased nonrenewable input makes the largest contribution to the total input (average value 60.73% of the total input), which mainly derived from agricultural mechanic equipments and chemical fertilizer; on the average, beans has the largest share (20.20%) to the total emergy output, next from rape seed (18.36%), then from peanuts (15.85%), fruits (15.74%), wheat (8.26%), rice (8.07%), corn (7.66%) and cotton (4.60%) accordingly, and the other four categories crops just have a contribution of 1.28%; the production efficiency of China's crop production system has been raised by 11.54% with decrease of the indicator unit emergy value of product (UEVP) from 1.82E09 sej/g to 1.61E09 sej/g, the dependence of this system on economic market has increased by 24.92% with growth of the indicator EIR from 6.22 to 7.77, its economic benefit has been reduced by 0.59% with decline of the indicator EYR from 1.69 to 1.68, and its environmental loading has raised by 57.89% with growth of the indicator ELR from 1.33 to 2.10; the sustainability of China's crop production system is reduced by 37.01% with decrease of the index ESI from 1.27 to 0.80, during this study period. Based on these study results, the following measures should be emphasized in future, including raising the efficiency of purchased non-renewable resources (especially agricultural mechanical equipments and chemical fertilizer), using other methods of cultivation inherently more sustainable (e.g. replacing chemical fertilizer with organic fertilizer, recycling organic wastes, biological control of agricultural pests, use of local renewable energy, and more), strengthening supervision of the related industrial processes and further promoting agricultural environmental protection.     

Energy and CO2 balance of maize and grass as energy crops for anaerobic digestion

Energy crops can be used to feed anaerobic digesters and produce renewable energy. However, sustainability of this option requires that it contributes to a net production of renewable energy and a net reduction of fossil CO2 emission. In this paper, the net balance of CO2 emission and renewable energy production is assessed for maize and grass energy crops produced in several agricultural systems relevant for Southern Belgium and surrounding areas. The calculated net energy yields are 8-25 (maize) and 7.4-15.5 (grass) MWh of renewable CH4 per MWh of fossil energy invested, depending on the agricultural option considered. After conversion to electricity, the specific CO2 emissions range from 31 to 104 kg(CO2)MWhelectricity(-1), depending on the case considered. This corresponds to a significant reduction in CO2 emissions compared to the current reference gas-steam turbine technology which produces 456 kg(CO2)MWhelectricity(-1).     

Emergy-based indicators of regional environmental sustainability: A case study in Shanwei,Guangdong, China

Understanding which factors mainly affect the environmental sustainability of a Region is a very crucial concern for many Chinese planners and policy-makers. In this study, the emergy accounting method is applied to the production and consumption activities of the city of Shanwei, a seaside urban area in Guangdong region, China. The emergy method provides a comprehensive assessment of a system, by generating a consistent set of indicators capable to capture the dynamics of the system as a whole and its efficiency in converting resources into an economic product and welfare. At the same time, the approach is capable to provide details about a system's performance over time, its use of renewable versus nonrenewables sources, local versus imported, concentrated versus dispersed and finally labor intensive versus fuel intensive processes. The main local renewable and nonrenewable emergy flows supporting the investigated area were included in the accounting, together with the flows of imported energy, goods, machinery, labor and services. Coal plays a crucial role for electricity generation, industrial uses, but also gasoline and diesel for transport affect the overall sustainability to a non-negligible extent. An Emergy Sustainability Indicator (ESI) of the local economic and social system is calculated and compared with the average value of the Chinese economy, based on the assumption that a process or system is unsustainable if it contributes to lower the overall sustainability of the region or country. This is quantified by the requirement that always must be ESI_local ≧ ESI_country. Results confirm that the most crucial factor for this region sustainability is the use of coal as a non-renewable and imported energy source. The calculated emergy indicators translate into a set-aside buffer land demand capable to mitigate, dilute, and uptake the environmental impact of human-dominated activities. Unfortunately, such buffer land demand is much higher than the land actually available. As a result, both the ESI-based sustainability equation as well as the lack of support land make the city's production and consumption patterns unsustainable and call for different lifestyles and environmental policies.     

21世纪以来闽三角城市群人类景观开发强度的时空演变——基于能值-GIS方法

在快速的城市化进程中,城市群作为城市发展到成熟阶段的高级空间组织形式,其在推进城市群区域社会经济一体化的同时,也在一定程度上加剧了城市群的人地关系矛盾和景观开发强度。为量化城市群的人类景观开发强度,揭示自然环境对人类资源消耗过程的压力响应机制,选取闽三角城市群在2000、2005和2013年的夜间灯光数据(DMSP/OLS)作为刻画人类经济活动范围的基础数据,通过能值分析理论,耦合可更新能源(太阳能、风能、地热能和降雨化学能等)与基于统计数据的不可更新能源进行能值核算,并进一步描述人类景观开发强度(Landscape development intensity,LDI)的时空演变特征,基于人类活动对自然生态系统的干扰程度划分为5级进行空间展示与分析。结果表明:(1)在时间尺度上,闽三角城市群的年可更新能值密度均值在2000、2005和2013年,分别为9.42×10~(16) sej/hm~2、7.25×10~(16) sej/hm~2和7.88×10~(16) sej/hm~2,呈现出先减后增的趋势,在空间尺度上,闽三角城市群可更新资源由环海湾地带向内陆地区呈环形逐层增加,其中在2000年表现尤为明显;(2)在不可更新资源的利用上,闽三角城市群的本地不可更新能源能值投入在2000、2005和2013年,分别为4.64×10~(24) sej、4.63×10~(24) sej和4.66×10~(24) sej,只出现轻微浮动,而外部输入能源的能值投入则在2000、2005和2013年,分别为1.41×10~(24) sej、3.18×10~(24) sej和5.71×10~(24) sej呈现逐年上升趋势,且其中对原煤的需求表现最高,占比高达90%;(3)LDI在空间分布上,自内陆至沿海干扰等级逐渐上升,其中,强度干扰与剧烈干扰主要覆盖厦门市、龙海市、晋江市和石狮市;在时间分布上,呈现出强度干扰和剧烈干扰逐渐增大的趋势。研究有助于政府对不同干扰等级区域的城乡建设与规划管理提供决策依据,为实现城市群可持续发展提供数据参考。     

Emergy synthesis of a combined food and energy production system compared to a conventional wheat (Triticum aestivum) production system

It is a major challenge to produce food and energy sustainably for the ever increasing world population as today's conventional food production and energy needs are met by the fossil based resources, causing enormous environmental load. A novel, combined food and energy (CFE) agro-ecosystem, was designed for sustainable production of food, fodder and energy without chemical inputs (fertiliser, herbicide and fungicide). The objective was an emergy synthesis of the CFE system compared to a conventional wheat (Triticum aestivum) production system to assess resource use efficiency. The emergy indices, used to assess the environmental performance and sustainability, exhibited contrasting differences between the two production systems in terms of outputs (Y), total emergy use, solar transformity, relative use of local renewable resources, environmental loading ratio (ELR), emergy yield ratio (EYR) and emergy sustainability index (ESI). The Y in the CFE consisted of grain, straw, fodder and woodchip production of 4020, 3580, 6100 and 10,000 kg/ha/yr respectively whereas Y in the conventional wheat consisted of 7250 and 3770 kg grain and straw/ha/yr respectively. The Y in the CFE was 81% (2.80E+11 J/ha/yr) higher with 13.5 times (6.40E+03 seJ/J) lower solar transformity compared to the Y (1.54E+11 J/ha/yr) and solar transformity (8.63E+04 seJ/J) in the conventional wheat, exhibiting highly resource intensive production in conventional wheat. The local renewables constituted 19.2% and 2.6% of the total emergy input in the CFE and the conventional wheat respectively with a corresponding lower ELR (4.21) and 22.5% higher EYR (1.26) in CFE compared to conventional wheat. CFE was more reliant on local renewable emergy flows and compatible with the local environment with higher ESI (0.30) compared to conventional wheat (0.03), where 64.5% of the total emergy input constituted chemical inputs. The study demonstrated that the innovative agro-ecosystem, exemplified by CFE, is considerably less resource demanding and more amenable to sustainable production, whether defined in terms of outputs, solar transformity, relative use of local renewable resources, EYR, ELR or ESI.     

Feasibility of using constructed treatment wetlands for municipal wastewater treatment in the Bogotá Savannah,Colombia

The main water bodies in the Bogotá Savannah have been seriously polluted due to the mismanagement of domestic, agricultural, and industrial wastewater. While there are a number of wastewater treatment facilities in the region, most do not function properly. There is a great need for inexpensive and sustainable wastewater treatment systems that are not technologically sophisticated and that do not require intensive management. The main goal of this study was to quantify the performance and sustainability of treatment wetlands and existing wastewater treatment systems in this region. Using data from the literature, a treatment wetland model was developed, which focused on pollutant removal. The modeled performance was compared to a system of waste stabilization ponds and a sequencing batch reactor. The three systems were subject to cost analysis and an emergy evaluation, leading to the assessment of indicators of cost-benefit for comparison. The economic analysis suggested that the net annual cost of the treatment wetland was US$ 14,672, compared to US$ 14,201 for the stabilization ponds and US$ 54,887 for the batch reactor. The emergy evaluations show that the ponds have the lowest annual emergy flow (6.65 + 16 sej/yr), followed by the constructed wetland (2.88E+17 sej/yr) and the batch reactor (8.86E+17 sej/yr). These results were combined to estimate treatment ratios (contaminants removed per lifetime cost, and contaminants removed per total emergy), cost ratios (cost per volume of water, annual cost per capita, and construction cost per capita), and emergy ratios (treatment yield, renewable emergy, lifetime emprice, construction emprice, non-renewable emergy, empower density, environmental loading, total emergy per volume of water, and emergy per capita).     

舟山市东极大黄鱼养殖系统能值评估

以能值理论为基础,选择浙江省舟山市东极大黄鱼养殖系统为研究对象,在定量分析大黄鱼养殖系统的物流和能流基础上,通过建立能值评价指标体系,综合评价了东极大黄鱼养殖系统对环境的影响及其可持续性.结果表明:东极大黄鱼养殖系统的太阳能值转换率TR为1.46× 106 sej/J,环境承载力ELR为91.10,能值投入的生产效率PEEl为6.91× 10-7,能值持续性指数ESI为0.011.东极大黄鱼养殖系统虽然生产效率较高,但是过分依赖于外部购买资源,并且系统对环境的压力较大,环境的持续性也较差.另外,与广东珠江口3个不同鱼种养殖系统的有关指标进行了对比,提出了大黄鱼养殖系统的可持续性发展建议.     

基于能值的沼气农业生态系统可持续发展水平综合评价——以恭城县为例

近年来,农村传统的粗放式发展模式对资源和环境造成了巨大的压力,严重阻碍农村的可持续发展进程,为此,国家在农村大力推行以沼气为重点的农村生态建设,加快建立以沼气为纽带的可持续农业发展模式。因此,对沼气农业生态系统的可持续性进行评价对农村能源生态建设和沼气工程的推广具有重要意义。本文选取广西恭城瑶族自治县沼气农业生态系统作为案例,将种植业、养殖业和生态旅游业作为一个复合生态系统,应用能值分析方法将不同能质的能量折算为统一的能值单位,分析了复合农业生态经济系统的可持续发展现状,通过能值分析发现案例区域恭城县沼气农业生态系统具有以下特点:(1)与传统农业生态系统相比,有机肥所占比重较大;(2)水果生产为当地主导产业,生态旅游业有了初步发展;(3)农业的快速发展使人民具有较高物质生活水平;(4)科技水平相对落后,生产率低;(5)沼气替代传统能源,大大减小了环境压力。通过对恭城县农业生态系统发展中的问题进行识别,提出相应政策建议,能够对其未来的发展模式提供参考,对沼气农业生态系统的推广具有重要意义。     

湖南省农业生态系统能值演变与趋势

应用能值分析方法,对1999-2008年湖南省农业生态系统的能值总量、投入和产出结构以及各能值指标的变化进行趋势分析.结果表明： 研究期间,湖南省农业生态系统总能值使用投入量基本保持平稳,但能值投入结构有变化,其中,不可更新工业辅助能值投入量由400E+22 sej增至5.53E+22 sej,可更新有机能值投入量由1.32E+23 sej降至1.20E+23 sej;系统能值产出总量和产出效率均有较大幅度的提高,2008年总能值产出达1.69E+23 sej,比1999年提高23.8%,净能值产出率由0.79升至0.96;由于环境负载率也呈不断上升的趋势（由1.12上升到1.79）,可持续发展指数呈缓慢下降趋势,由0.71降至0.54,说明湖南省农业总体属于高消费驱动型生态系统,具有较明显的粗放式发展特征.