土地利用变化对城郊农业区生态效益的影响——以四川省南充市高坪区为例

借鉴生态效益综合评价的有关理论和数学模型,以四川省南充市高坪区为例,选取生物多样性指数、植被覆盖指数、水土保持效益指数、土壤改良指数、涵养水源指数、拦截径流指数和湿度指数7个指标作为评价因子,建立生态效益评价体系,对该区域1996和2005年2个时期综合生态效益进行评估和比较.结果表明,该区域综合生态效益值分别为7.85和7.95,2005年比1996年略为升高;基于GIS的图层叠置、分割等分析功能,就区域土地利用变化对其内部生态效益造成的变化进行了分析,该区域可被划分为生态效益显著增强区、增强区、保持区、减弱区和显著减弱区5个等级.     

集约化农区经济发展对耕地土壤有机碳含量变化的影响

陆地生态系统土壤有机碳储量变化是全球气候变化研究的重要方面,而耕地土壤有机碳含量是当中最活跃的部分,与人类利用行为以及社会经济发展水平相联系。文章选取黄淮海平原的北京市大兴区、河北省曲周县和黄土高原的山西省兴县的446个耕作层土壤20世纪80年代和2000年的有机碳含量数据和当地的社会经济、投入产出资料,结果表明:20年来,不同区域耕地土壤有机碳含量存在空间变异,但是其空间分布格局并未发生变化;对土地的集约利用并未造成土壤有机碳含量的降低,相反,各区域土壤有机碳含量普遍增加。结合相应的农户调查和统计资料,发现区域经济发展强烈地影响着土壤有机碳储量发生变化。无论自然条件优劣,还是经济发展水平处于何种阶段,经济的发展都能够促使农户增加对土地的投入,经济发达地区有充足的资金和市场保障,通过农业结构调整会增加对土地的投入;经济落后地区追求作物高产,促使土地投入也不断增加;使得作物经济产量和生物产量获得提高,促使耕地土壤有机碳含量增加。     

Motivations for the Restoration of Ecosystems

Abstract:  The reasons ecosystems should be restored are numerous, disparate, generally understated, and commonly underappreciated. We offer a typology in which these reasons—or motivations—are ordered among five rationales: technocratic, biotic, heuristic, idealistic, and pragmatic. The technocratic rationale encompasses restoration that is conducted by government agencies or other large organizations to satisfy specific institutional missions and mandates. The biotic rationale for restoration is to recover lost aspects of local biodiversity. The heuristic rationale attempts to elicit or demonstrate ecological principles and biotic expressions. The idealistic rationale consists of personal and cultural expressions of concern or atonement for environmental degradation, reengagement with nature, and/or spiritual fulfillment. The pragmatic rationale seeks to recover or repair ecosystems for their capacity to provide a broad array of natural services and products upon which human economies depend and to counteract extremes in climate caused by ecosystem loss. We propose that technocratic restoration, as currently conceived and practiced, is too narrow in scope and should be broadened to include the pragmatic rationale whose overarching importance is just beginning to be recognized. We suggest that technocratic restoration is too authoritarian, that idealistic restoration is overly restricted by lack of administrative strengths, and that a melding of the two approaches would benefit both. Three recent examples are given of restoration that blends the technocratic, idealistic, and pragmatic rationales and demonstrates the potential for a more unified approach. The biotic and heuristic rationales can be satisfied within the contexts of the other rationales.     

Deforestation and Plant Diversity of Madagascar's Littoral Forests

Abstract:  Few studies have attempted to quantify the reduction or document the floristic composition of forests in Madagascar. Thus, we focused specifically on deforestation and plant diversity in Madagascar's eastern littoral community. We used a data set of approximately 13,500 specimen records compiled from both historical and contemporary collections resulting from recent intensive inventory efforts to enumerate total plant species richness and to analyze the degree of endemism within littoral forests. Change in littoral forest cover from original to current extent was estimated using geographical information systems tools, remote sensing data (satellite imagery and low-elevation digital photography), and environmental data layers. Of the original littoral forest only 10.3% remains in the form of small forest parcels, and only 1.5% of these remaining fragments are included within the existing protected-areas network. Additionally, approximately 13% of Madagascar's total native flora has been recorded from these forests that originally occupied <1% of its total land surface, and over 25% of the 1535 plant species known from littoral forests are endemic to this community. Given the ongoing pressure from human settlement along Madagascar's eastern coast, protection of the remaining forest fragments is critical for their survival. Fifteen of the largest intact littoral forest fragments we identified, collectively representing 41.5% of remaining littoral forest, are among priority sites recommended to the government of Madagascar for plant conservation and incorporation into the protected-areas network.     

Adjustment costs from environmental change

The paper is concerned with the case whereby the distribution of a firm's productivity shocks changes without the knowledge of the firm. Over time the firm learns about the nature and extent of the change in the distribution of the shock and adjusts, incurring adjustment costs in the process. The long-run loss in profits (±) due to the shift in the distribution we term the equilibrium response. The transitory loss in profits, incurred while the firm is learning about the distribution shift, is termed the adjustment cost. The theory is then applied to the problem of measuring adjustment costs in the face of imperfectly observed climate change in agriculture. The empirical part of the paper involves estimating a restricted profit function for agricultural land in a five-state region of the Midwest US as a function of prices, land characteristics, actual weather realizations and expected weather. We then simulate the effect of an unobserved climate shock, where learning about the climate shock is by observing the weather and updating prior knowledge using Bayes Rule. We find adjustment costs to climate change are 1.4% of annual land rents.     

Clearing the air: The costs and consequences of higher CAFE standards and increased gasoline taxes

Concerns about energy security and climate change have sparked legislators’ interest in reducing gasoline consumption by increasing corporate average fuel-economy (CAFE) standards. Using an empirically rich simulation model and cost estimates for anticipated fuel-economy technologies, we estimate annual costs of reducing long-run gasoline consumption by 10% via a 3.8 miles per gallon increase in the standards, and the potential cost savings from allowing manufacturers to buy and sell fuel-economy credits. Maximum gasoline savings would be realized only after all existing vehicles were replaced, or 14 years in our model. A gasoline tax would produce greater immediate savings by encouraging people to drive less, and eventually to choose more-fuel-efficient vehicles. We demonstrate the advantage of a tax by comparing the cost of the higher CAFE standards over the first 14 years against the cost of a gasoline tax that would save the same amount of gasoline over that time.     

沂河流域土地利用时空变化图谱特征分析

基于沂河流域1995年、2005年和2015年土地利用空间数据,运用地学信息图谱方法构建1995-2005年和2005-2015年两个时序单元的土地利用转移图谱和涨落势图谱,分析了沂河流域近20年来的土地利用时空变化规律及发展过程。结果表明：（1）1995-2015年,沂河流域土地利用结构以耕地和林地为主,其中耕地和草地减少,林地和建设用地增加是主要变化趋势。（2）土地利用转移图谱以耕地与林地、草地之间的相互转换以及建设用地占用耕地为主,林地、草地转变为耕地主要发生在费县和平邑县中部地势平缓的山前平原,耕地转变为林地、草地则主要分布于研究区北部和西南部土壤侵蚀较为严重的山区,耕地转变为建设用地主要集中在各县市城区周边经济相对发达的区域。两个时序单元中,发生变化的主要图谱单元类型及面积存在显著差异,2005-2015年土地利用发生转换的空间进一步扩张。（3）土地利用涨势图谱中新增耕地面积最大,占新增面积的比例为33.87%;落势图谱中耕地萎缩面积最大,占萎缩面积的比例为51.38%。两个时序单元中,各县市涨落势图谱变化存在明显差异。该研究可为沂河流域土地资源的可持续利用及生态建设提供科学依据。     

Why a 100-Year Time Horizon should be used for GlobalWarming Mitigation Calculations

Global warming mitigation calculationsrequire consistent procedures for handlingtime in order to compare `permanent' gainsfrom energy-sector mitigation options with`impermanent' gains from many forest-sectoroptions. A critical part of carbonaccounting methodologies such as thosebased on `ton-years' (the product of thenumber of tons of carbon times the numberof years that each ton is held out of theatmosphere) is definition of a timehorizon, or the time period over whichcarbon impacts and benefits are considered. Here a case is made for using a timehorizon of 100 years. This choice avoidsdistortions created by much longer timehorizons that would lead to decisionsinconsistent with societal behavior inother spheres; it also avoids a rapidincrease in the implied value of time ifhorizons shorter than 100 years are used.Selection of a time horizon affectsdecisions on financial mechanisms andcarbon credit. Simple adaptations canallow a time horizon to be specified andused to calculate mitigation benefits andat the same time reserve a given percentageof weight in decision making forgenerations beyond the end of the timehorizon. The choice of a time horizon willheavily influence whether mitigationoptions such as avoided deforestation areconsidered viable.     

呼和浩特市地表水水质变化趋势分析

对黄河(过境)、大黑河水系及浑河水系十年水质检测结果进行综合分析,揭示其变化趋势,并针对各河流污染断面提出急需解决的问题.     

Revisit ocean thermal energy conversion system

The earth, covered more than70.8% by the ocean, receives most of itsenergy from the sun. Solar energy istransmitted through the atmosphere andefficiently collected and stored in thesurface layer of the ocean, largely in thetropical zone. Some of the energy isre-emitted to the atmosphere to drive thehydrologic cycle and wind. The wind fieldreturns some of the energy to the ocean inthe form of waves and currents. Themajority of the absorbed solar energy isstored in vertical thermal gradients nearthe surface layer of the ocean, most ofwhich is in the tropical region. Thisthermal energy replenished each day by thesun in the tropical ocean represents atremendous pollution-free energy resourcefor human civilization. Ocean ThermalEnergy Conversion (OTEC) technology refersto a mechanical system that utilizes thenatural temperature gradient that exists inthe tropical ocean between the warm surfacewater and the deep cold water, to generateelectricity and produce other economicallyvaluable by-products. The science andengineering behind OTEC have been studiedin the US since the mid-seventies,supported early by the U.S. Government andlater by State and private industries.There are two general types of OTECdesigns: closed-cycle plants utilize theevaporation of a working fluid, such asammonia or propylene, to drive theturbine-generator, and open-cycle plantsuse steam from evaporated sea water to runthe turbine. Another commonly known design,hybrid plants, is a combination of the two.OTEC requires relatively low operation andmaintenance costs and no fossil fuelconsumption.OTEC system possesses a formidablepotential capacity for renewable energy andoffers a significant elimination ofgreenhouse gases in producing power. Inaddition to electricity and drinking water,an OTEC system can produce many valuableby-products and side-utilizations, such as:hydrogen, air-conditioning, ice,aquaculture, and agriculture, etc. Thepotential of these by-products, especiallydrinking water, aquaculture andmariculture, can easily translate intobillions of dollars in businessopportunities. The current status of theOTEC system definitely deserves to becarefully revisited. This paper willexamine recent major advancements intechnology, evaluate costs andeffectiveness, and assess the overallmarket environment of the OTEC system anddescribe its great renewable energypotential and overall benefits to thenations of the world.