近期和长远时段内北极生态系统结构受到的影响

生物在物种水平上对全球气候变暖和紫外线B(UV-B)辐射增强的反应受到其群落内其他物种以及生态系统内养分循环的调节,所有的这些反应将会导致生态系统结构的变化.根据高纬度地区坏境因子的可能变化而做的控制试验表明,由夏季变暖而引起苔原植被的变化要小于增加施肥而引起的变化,试验涉及的某些环境因子对北极生态系统的结构有非常强烈地影响,但是这些影响因地区而异,观测结果表明,处于最寒冷地区的植物群落和无脊椎动物群落对全球气候变暖和紫外线B辐射的增强反应最为强烈.尽管微生物量和养分储存量相对稳定,北极无脊椎动物群落还是很可能会对全球变暖产生迅速的反应.试验结果显示,加强紫外线B辐射会改变革兰氏阴性细菌和真菌的群落组成结构,但不会对植物群落的组成产生影响.由夏季气温升高而提高的植物生产力将会控制食物网的动态变化,以苔原植被和亚极地森林植物为基础的食物网中的营养流动会明显地影响到几种优势动物种群数量的周期性波动,在某些年分这些动物的种群数量会达到峰值.小型啮齿动物和食叶昆虫如秋毛虫种群数量的周期性变化则会影响苔原和森林苔原植物的组成结构和多样性,同时也会影响到一些专性捕食者和寄生虫的变化.在暖冬,雪表形成冰壳可能会减少旅鼠的植物食物来源,然而较深的雪也可以使它们免受雪地表面上捕食者对它们的捕食.在芬诺斯堪的亚地区,已有证据表明小型啮齿类动物群落结构和种群动态的显著变化会导致专门以小型啮齿类动物为食物的捕食者的数量减少.气候还可能改变昆虫在白桦森林生态系统中的作用,因为暖冬可以增加这些昆虫卵的成活率,并且扩大其分布范围.此外,在夏季困扰驯鹿的昆虫会由于夏季气候的变暖而扩大其分布范围、增加种群数量并且种群更为活跃;同时在另一方面也会对驯鹿不利,即那些昔日驯鹿/北美驯鹿的避难场所--冰川和未融的成片的雪--在这样温暖的夏季则可能会消失.     

近期和长远时段内北极生态系统功能受到的影响

长期以来,就营养物质和碳循环而言,北极生态系统降低了初级生产力；能量,水和温室气体交换的水平已引起了局部和区域性的小幅度降温.大气CO2中的碳沉积在广袤而寒冷的有机土壤中,冰雪覆盖的低矮植被产生高的反射率,都影响了局部气候.然而,北极生态系统功能的许多方面都对气候变化及其产生的生物多样性影响敏感.当前的北极气候导致了低的有机物质分解速率,因此,尽管有机物和元素输入量较低,但北极生态系统还是趋向于积累有机物和元素,土壤中氮和磷等可利用元素结果成为促进碳固定以及生物量和有机物进一步积累的关键性限制因素.气候变暖可能增加特别是土壤中的碳和元素的周转,起初可能导致元素的丢失,但最后会慢慢的恢复.在北极生态系统中,单个物种和物种多样性已经明显地影响了元素的输入和滞留,另一方面,从长远来看,尽管CO2和紫外线增加对植物组织化学、分解和氮固定的影响可能变得重要,但对整个生态系统来说,影响可能很小.碳循环的示踪气体主要形式是CO2和CH4,大多数碳以CO2的形式损失,这些CO2是由植物和土壤生物产生.来自潮湿苔原生态系统以CH4形式释放的碳大约是CO2形式的5％,而且在没有任何其他变化的情况下,对变暖作出响应.冬天过程和植物类型也影响CH4释放和能量在生物圈和大气之间的交换,因为反射率从冬末到夏天存在很大的变化,在冬末,雪反射了入射的大部分光线,在夏天,生态系统吸收了入射的大部分光线,所以在所有的陆地生态系统中,北极生态系统在能量交换方面表现出巨大的季节性变化.植被深刻地影响北极生态系统水和能量交换.在冰雪覆盖期间,反射率从苔原、森林苔原、落叶林、常绿林依次降低.灌木和树增加了雪的深度,反过来又使冬天的土壤温度增加,因此,由气候变化而引起的未来植被方面的变化很可能深远地改变区域的气候.     

Prevalence of chromosomal aberrations in Argentinean agricultural workers

Environmental Science and Pollution Research - Little is known about biosecurity measures and toxic effects during pesticide application in the province of Jujuy, Argentina, particularly concerning...     

Dimethoate induces genotoxicity as a result of oxidative stress: in vivo and in vitro studies

Environmental Science and Pollution Research - Dimethoate ([O,O-dimethyl S-(N-methylcarbamoylmethyl) phosphorodithioate]) is an organophosphate insecticide and acaricide widely used for...     

Uncertainties and recommendations

An assessment of the impacts of changes in climate and UV-B radiation on Arctic terrestrial ecosystems, made within the Arctic Climate Impacts Assessment (ACIA), highlighted the profound implications of projected warming in particular for future ecosystem services, biodiversity and feedbacks to climate. However, although our current understanding of ecological processes and changes driven by climate and UV-B is strong in some geographical areas and in some disciplines, it is weak in others. Even though recently the strength of our predictions has increased dramatically with increased research effort in the Arctic and the introduction of new technologies, our current understanding is still constrained by various uncertainties. The assessment is based on a range of approaches that each have uncertainties, and on data sets that are often far from complete. Uncertainties arise from methodologies and conceptual frameworks, from unpredictable surprises, from lack of validation of models, and from the use of particular scenarios, rather than predictions, of future greenhouse gas emissions and climates. Recommendations to reduce the uncertainties are wide-ranging and relate to all disciplines within the assessment. However, a repeated theme is the critical importance of achieving an adequate spatial and long-term coverage of experiments, observations and monitoring of environmental changes and their impacts throughout the sparsely populated and remote region that is the Arctic.     

MANAGEMENT OF WATER QUALITY IN RELEASES FROM SOUTHWESTERN IMPOUNDMENTS1

ABSTRACT. The objective of this investigation was to determine the selectivity of withdrawal which is possible in southwestern reservoirs. Two stratified flow solutions were examined to test their applicability under field conditions. Although both appeared capable of accurate prediction of the outflow velocity profile, the Bohan-Grace solution, which required less input data, was utilized to predict the chemical constituents of single and simultaneous releases from several southwestern impoundments. Prediction of outflow water quality was within fifteen percent for southwestern reservoirs as shallow as fifty-five feet. The withdrawal layer thickness for the subject Texas impoundments included the entire hypolimnion or epilmnion depending on outlet location. The sensitivity of the velocity profile to seasonal changes, reservoir discharge rate and withdrawal port dimensions also is illustrated.     

Climate engineering and human rights

ABSTRACT

In this Forum, three scholars discuss how climate engineering will pose novel human rights challenges, and may well force reconsideration of how human rights are applied as a guide to action. Following a short introduction, the first section introduces three competing approaches to human rights, arguing views which emphasize fairness or attempt to maximize satisfaction are more promising than one viewing human rights as inviolable ‘side-constraints’. The second section draws lessons from climate migration that are relevant for climate engineering in terms of incorporating a human rights approach to duties, rights, and participation. The final section compares the ‘needs-based’ and ‘rights-based’ approaches to humanitarian work in the face of climate change and climate engineering, raising concerns for duty-bearers and right-holders. The Forum’s conclusion draws together points of overlap and suggests a path forward for policy and research on this topic.     

Synthesis of effects in four Arctic subregions

An assessment of impacts on Arctic terrestrial ecosystems has emphasized geographical variability in responses of species and ecosystems to environmental change. This variability is usually associated with north-south gradients in climate, biodiversity, vegetation zones, and ecosystem structure and function. It is clear, however, that significant east-west variability in environment, ecosystem structure and function, environmental history, and recent climate variability is also important. Some areas have cooled while others have become warmer. Also, east-west differences between geographical barriers of oceans, archipelagos and mountains have contributed significantly in the past to the ability of species and vegetation zones to relocate in response to climate changes, and they have created the isolation necessary for genetic differentiation of populations and biodiversity hot-spots to occur. These barriers will also affect the ability of species to relocate during projected future warming. To include this east-west variability and also to strike a balance between overgeneralization and overspecialization, the ACIA identified four major sub regions based on large-scale differences in weather and climate-shaping factors. Drawing on information, mostly model output that can be related to the four ACIA subregions, it is evident that geographical barriers to species re-location, particularly the distribution of landmasses and separation by seas, will affect the northwards shift in vegetation zones. The geographical constraints--or facilitation--of northward movement of vegetation zones will affect the future storage and release of carbon, and the exchange of energy and water between biosphere and atmosphere. In addition, differences in the ability of vegetation zones to re-locate will affect the biodiversity associated with each zone while the number of species threatened by climate change varies greatly between subregions with a significant hot-spot in Beringia. Overall, the subregional synthesis demonstrates the difficulty of generalizing projections of responses of ecosystem structure and function, species loss, and biospheric feedbacks to the climate system for the whole Arctic region and implies a need for a far greater understanding of the spatial variability in the responses of terrestrial arctic ecosystems to climate change.     

Making index insurance attractive to farmers

There are several factors that influence whether people will want to participate in index insurance programs. A number of these influence their attractiveness on economic grounds, including both the size and timing of the premium and potential payouts, and the degree of risk aversion of the potential customers. Other factors make programs attractive for reasons that are not economic, but no less valid. These have to do with the trust that people have in the insurance product and the organizations involved in selling and managing it. Indeed, data from India, Africa, and South America show that these factors may be more important than the economic ones in influencing demand. Index insurance pilot projects, in order to estimate demand for alternative products, have typically involved a great deal of interaction with potential customers. It is important to recognize that such interaction is crucial not just as a research tool, but also as a means to build understanding and trust in the products. When scaling up from isolated pilots to operational programs, it is vital to recognize this trust building function by replicating participation efforts in every community. In this paper, we examine the role of field games in establishing and building trust in three important aspects of these projects for participants: trust in the insurance product, trust in the participating organizations, and trust in their own ability to make good decisions. While games have previously been used as a way to gauge interest in the product and to identify design features, we argue that these games are also valuable tools for constructing these kinds of trust.     

Experimental evidence that workers recognize reproductives through cuticular hydrocarbons in the ant Odontomachus brunneus

Eusociality is characterized by a reproductive division of labor, wherein workers respond to the presence of reproductive individuals by refraining from reproduction themselves and restricting the reproductive efforts of others. Our understanding of how eusociality is maintained therefore depends on characterizing the mechanism by which workers detect the presence of a reproductive. Variations in cuticular hydrocarbons correspond to changes in reproductive ability in ants, and experimental studies are beginning to reveal the function of hydrocarbons as signals. In this study, we compare the cuticular hydrocarbon profiles of dominant and reproductive workers and queens of the ant Odontomachus brunneus with profiles of non-reproductive workers. Using split/reunification tests we document the existence of worker policing in both queenless and queenright colonies; supernumerary reproductives were treated aggressively by nestmates. Finally, we induce aggression and replicate queen-like submissive nestmate responses by supplementing the hydrocarbon profile of workers with (Z)-9-nonacosene, a compound that was significantly more abundant on the cuticles of reproductives. In three bioassays, we compare this manipulation to various control manipulations of the hydrocarbon profile and demonstrate that workers gauge the reproductive activity of nestmates through changes in their cuticular hydrocarbon profiles.